- Flutter - Discussion
- Flutter - Useful Resources
- Flutter - Quick Guide
- Flutter - Conclusion
- Flutter - Writting Advanced Applications
- Flutter - Development Tools
- Flutter - Deployment
- Flutter - Testing
- Flutter - Internationalization
- Flutter - Database Concepts
- Flutter - Accessing REST API
- Flutter - Introduction to Package
- Flutter - Writing IOS Specific Code
- Flutter - Writing Android Specific Code
- Flutter - Animation
- Flutter - State Management
- Flutter - Introduction to Gestures
- Flutter - Introduction to Layouts
- Flutter - Introduction to Widgets
- Introduction to Dart Programming
- Flutter - Architecture Application
- Creating Simple Application in Android Studio
- Flutter - Installation
- Flutter - Introduction
- Flutter - Home
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
Flutter - Quick Guide
Flutter - Introduction
In general, developing a mobile apppcation is a complex and challenging task. There are many frameworks available to develop a mobile apppcation. Android provides a native framework based on Java language and iOS provides a native framework based on Objective-C / Swift language.
However, to develop an apppcation supporting both the OSs, we need to code in two different languages using two different frameworks. To help overcome this complexity, there exists mobile frameworks supporting both OS. These frameworks range from simple HTML based hybrid mobile apppcation framework (which uses HTML for User Interface and JavaScript for apppcation logic) to complex language specific framework (which do the heavy pfting of converting code to native code). Irrespective of their simppcity or complexity, these frameworks always have many disadvantages, one of the main drawback being their slow performance.
In this scenario, Flutter – a simple and high performance framework based on Dart language, provides high performance by rendering the UI directly in the operating system’s canvas rather than through native framework.
Flutter also offers many ready to use widgets (UI) to create a modern apppcation. These widgets are optimized for mobile environment and designing the apppcation using widgets is as simple as designing HTML.
To be specific, Flutter apppcation is itself a widget. Flutter widgets also supports animations and gestures. The apppcation logic is based on reactive programming. Widget may optionally have a state. By changing the state of the widget, Flutter will automatically (reactive programming) compare the widget’s state (old and new) and render the widget with only the necessary changes instead of re-rendering the whole widget.
We shall discuss the complete architecture in the coming chapters.
Features of Flutter
Flutter framework offers the following features to developers −
Modern and reactive framework.
Uses Dart programming language and it is very easy to learn.
Fast development.
Beautiful and fluid user interfaces.
Huge widget catalog.
Runs same UI for multiple platforms.
High performance apppcation.
Advantages of Flutter
Flutter comes with beautiful and customizable widgets for high performance and outstanding mobile apppcation. It fulfills all the custom needs and requirements. Besides these, Flutter offers many more advantages as mentioned below −
Dart has a large repository of software packages which lets you to extend the capabipties of your apppcation.
Developers need to write just a single code base for both apppcations (both Android and iOS platforms). Flutter may to be extended to other platform as well in the future.
Flutter needs lesser testing. Because of its single code base, it is sufficient if we write automated tests once for both the platforms.
Flutter’s simppcity makes it a good candidate for fast development. Its customization capabipty and extendibipty makes it even more powerful.
With Flutter, developers has full control over the widgets and its layout.
Flutter offers great developer tools, with amazing hot reload.
Disadvantages of Flutter
Despite its many advantages, flutter has the following drawbacks in it −
Since it is coded in Dart language, a developer needs to learn new language (though it is easy to learn).
Modern framework tries to separate logic and UI as much as possible but, in Flutter, user interface and logic is intermixed. We can overcome this using smart coding and using high level module to separate user interface and logic.
Flutter is yet another framework to create mobile apppcation. Developers are having a hard time in choosing the right development tools in hugely populated segment.
Flutter - Installation
This chapter will guide you through the installation of Flutter on your local computer in detail.
Installation in Windows
In this section, let us see how to install Flutter SDK and its requirement in a windows system.
Step 1 − Go to URL,
and download the latest Flutter SDK. As of April 2019, the version is 1.2.1 and the file is flutter_windows_v1.2.1-stable.zip.Step 2 − Unzip the zip archive in a folder, say C:flutter
Step 3 − Update the system path to include flutter bin directory.
Step 4 − Flutter provides a tool, flutter doctor to check that all the requirement of flutter development is met.
flutter doctor
Step 5 − Running the above command will analyze the system and show its report as shown below −
Doctor summary (to see all details, run flutter doctor -v): [√] Flutter (Channel stable, v1.2.1, on Microsoft Windows [Version 10.0.17134.706], locale en-US) [√] Android toolchain - develop for Android devices (Android SDK version 28.0.3) [√] Android Studio (version 3.2) [√] VS Code, 64-bit edition (version 1.29.1) [!] Connected device ! No devices available ! Doctor found issues in 1 category.
The report says that all development tools are available but the device is not connected. We can fix this by connecting an android device through USB or starting an android emulator.
Step 6 − Install the latest Android SDK, if reported by flutter doctor
Step 7 − Install the latest Android Studio, if reported by flutter doctor
Step 8 − Start an android emulator or connect a real android device to the system.
Step 9 − Install Flutter and Dart plugin for Android Studio. It provides startup template to create new Flutter apppcation, an option to run and debug Flutter apppcation in the Android studio itself, etc.,
Open Android Studio.
Cpck File → Settings → Plugins.
Select the Flutter plugin and cpck Install.
Cpck Yes when prompted to install the Dart plugin.
Restart Android studio.
Installation in MacOS
To install Flutter on MacOS, you will have to follow the following steps −
Step 1 − Go to URL,
and download latest Flutter SDK. As of April 2019, the version is 1.2.1 and the file is flutter_macos_v1.2.1- stable.zip.Step 2 − Unzip the zip archive in a folder, say /path/to/flutter
Step 3 − Update the system path to include flutter bin directory (in ~/.bashrc file).
> export PATH = "$PATH:/path/to/flutter/bin"
Step 4 − Enable the updated path in the current session using below command and then verify it as well.
source ~/.bashrc source $HOME/.bash_profile echo $PATH
Flutter provides a tool, flutter doctor to check that all the requirement of flutter development is met. It is similar to the Windows counterpart.
Step 5 − Install latest XCode, if reported by flutter doctor
Step 6 − Install latest Android SDK, if reported by flutter doctor
Step 7 − Install latest Android Studio, if reported by flutter doctor
Step 8 − Start an android emulator or connect a real android device to the system to develop android apppcation.
Step 9 − Open iOS simulator or connect a real iPhone device to the system to develop iOS apppcation.
Step 10 − Install Flutter and Dart plugin for Android Studio. It provides the startup template to create a new Flutter apppcation, option to run and debug Flutter apppcation in the Android studio itself, etc.,
Open Android Studio
Cpck Preferences → Plugins
Select the Flutter plugin and cpck Install
Cpck Yes when prompted to install the Dart plugin.
Restart Android studio.
Creating Simple Apppcation in Android Studio
In this chapter, let us create a simple Flutter apppcation to understand the basics of creating a flutter apppcation in the Android Studio.
Step 1 − Open Android Studio
Step 2 − Create Flutter Project. For this, cpck File → New → New Flutter Project
![New Flutter Project](/flutter/images/new_flutter_project.jpg)
Step 3 − Select Flutter Apppcation. For this, select Flutter Apppcation and cpck Next.
![Flutter Apppcation Next](/flutter/images/flutter_apppcation_next.jpg)
Step 4 − Configure the apppcation as below and cpck Next.
Project name: hello_app
Flutter SDK Path: <path_to_flutter_sdk>
Project Location: <path_to_project_folder>
Description: Flutter based hello world apppcation
![Project Name](/flutter/images/project_name.jpg)
Step 5 − Configure Project.
Set the company domain as flutterapp.tutorialspoint.com and cpck Finish.
Step 6 − Enter Company domain.
Android Studio creates a fully working flutter apppcation with minimal functionapty. Let us check the structure of the apppcation and then, change the code to do our task.
The structure of the apppcation and its purpose is as follows −
![Structure Apppcation](/flutter/images/structure_apppcation.jpg)
Various components of the structure of the apppcation are explained here −
android − Auto generated source code to create android apppcation
ios − Auto generated source code to create ios apppcation
pb − Main folder containing Dart code written using flutter framework
ib/main.dart − Entry point of the Flutter apppcation
test − Folder containing Dart code to test the flutter apppcation
test/widget_test.dart − Sample code
.gitignore − Git version control file
.metadata − auto generated by the flutter tools
.packages − auto generated to track the flutter packages
.iml − project file used by Android studio
pubspec.yaml − Used by Pub, Flutter package manager
pubspec.lock − Auto generated by the Flutter package manager, Pub
README.md − Project description file written in Markdown format
Step 7 − Replace the dart code in the pb/main.dart file with the below code −
import package:flutter/material.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { // This widget is the root of your apppcation. @override Widget build(BuildContext context) { return MaterialApp( title: Hello World Demo Apppcation , theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage(title: Home page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.title), ), body: Center( child: Text( Hello World , ) ), ); } }
Let us understand the dart code pne by pne.
Line 1 − imports the flutter package, material. The material is a flutter package to create user interface according to the Material design guidepnes specified by Android.
Line 3 − This is the entry point of the Flutter apppcation. Calls runApp function and pass it an object of MyApp class. The purpose of the runApp function is to attach the given widget to the screen.
Line 5-17 − Widget is used to create UI in flutter framework. StatelessWidget is a widget, which does not maintain any state of the widget. MyApp extends StatelessWidget and overrides its build method. The purpose of the build method is to create a part of the UI of the apppcation. Here, build method uses MaterialApp, a widget to create the root level UI of the apppcation. It has three properties - title, theme and home.
title is the title of the apppcation
theme is the theme of the widget. Here, we set blue as the overall color of the apppcation using ThemeData class and its property, primarySwatch.
home is the inner UI of the apppcation, which we set another widget, MyHomePage
Line 19 - 38 − MyHomePage is same as MyApp except it returns Scaffold Widget. Scaffold is a top level widget next to MaterialApp widget used to create UI conforming material design. It has two important properties, appBar to show the header of the apppcation and body to show the actual content of the apppcation. AppBar is another widget to render the header of the apppcation and we have used it in appBar property. In body property, we have used Center widget, which centers it child widget. Text is the final and inner most widget to show the text and it is displayed in the center of the screen.
Step 8 − Now, run the apppcation using, Run → Run main.dart
![Main Dart](/flutter/images/main_dart.jpg)
Step 9 − Finally, the output of the apppcation is as follows −
![Home Page](/flutter/images/home_page.jpg)
Flutter - Architecture Apppcation
In this chapter, let us discuss the architecture of the Flutter framework.
Widgets
The core concept of the Flutter framework is In Flutter, Everything is a widget. Widgets are basically user interface components used to create the user interface of the apppcation.
In Flutter, the apppcation is itself a widget. The apppcation is the top- level widget and its UI is build using one or more children (widgets), which again build using its children widgets. This composabipty feature helps us to create a user interface of any complexity.
For example, the widget hierarchy of the hello world apppcation (created in previous chapter) is as specified in the following diagram −
![Hello World Apppcation](/flutter/images/hello_world_apppcation.jpg)
Here the following points are worth notable −
MyApp is the user created widget and it is build using the Flutter native widget, MaterialApp.
MaterialApp has a home property to specify the user interface of the home page, which is again a user created widget, MyHomePage.
MyHomePage is build using another flutter native widget, Scaffold
Scaffold has two properties – body and appBar
body is used to specify its main user interface and appBar is used to specify its header user interface
Header UI is build using flutter native widget, AppBar and Body UI is build using Center widget.
The Center widget has a property, Child, which refers the actual content and it is build using Text widget
Gestures
Flutter widgets support interaction through a special widget, GestureDetector. GestureDetector is an invisible widget having the abipty to capture user interactions such as tapping, dragging, etc., of its child widget. Many native widgets of Flutter support interaction through the use of GestureDetector. We can also incorporate interactive feature into the existing widget by composing it with the GestureDetector widget. We will learn the gestures separately in the upcoming chapters.
Concept of State
Flutter widgets support State maintenance by providing a special widget, StatefulWidget. Widget needs to be derived from StatefulWidget widget to support state maintenance and all other widget should be derived from StatefulWidget. Flutter widgets are reactive in native. This is similar to reactjs and StatefulWidget will be auto re- rendered whenever its internal state is changed. The re-rendering is optimized by finding the difference between old and new widget UI and rendering only the necessary changes
Layers
The most important concept of Flutter framework is that the framework is grouped into multiple category in terms of complexity and clearly arranged in layers of decreasing complexity. A layer is build using its immediate next level layer. The top most layer is widget specific to Android and iOS. The next layer has all flutter native widgets. The next layer is Rendering layer, which is low level renderer component and renders everything in the flutter app. Layers goes down to core platform specific code
The general overview of a layer in Flutter is specified in the below diagram −
![Overview Of Layer](/flutter/images/overview_of_layer.jpg)
The following points summarize the architecture of Flutter −
In Flutter, everything is a widget and a complex widget is composed of already existing widgets.
Interactive features can be incorporated whenever necessary using GestureDetector widget.
The state of a widget can be maintained whenever necessary using StatefulWidget widget.
Flutter offers layered design so that any layer can be programmed depending on the complexity of the task.
We will discuss all these concepts in detail in the upcoming chapters.
Flutter - Introduction to Dart Programming
Dart is an open-source general-purpose programming language. It is originally developed by Google. Dart is an object-oriented language with C-style syntax. It supports programming concepts pke interfaces, classes, unpke other programming languages Dart doesn’t support arrays. Dart collections can be used to reppcate data structures such as arrays, generics, and optional typing.
The following code shows a simple Dart program −
void main() { print("Dart language is easy to learn"); }
Variables and Data types
Variable is named storage location and Data types simply refers to the type and size of data associated with variables and functions.
Dart uses var keyword to declare the variable. The syntax of var is defined below,
var name = Dart ;
The final and const keyword are used to declare constants. They are defined as below −
void main() { final a = 12; const pi = 3.14; print(a); print(pi); }
Dart language supports the following data types −
Numbers − It is used to represent numeric pterals – Integer and Double.
Strings − It represents a sequence of characters. String values are specified in either single or double quotes.
Booleans − Dart uses the bool keyword to represent Boolean values – true and false.
Lists and Maps − It is used to represent a collection of objects. A simple List can be defined as below −.
void main() { var pst = [1,2,3,4,5]; print(pst); }
The pst shown above produces [1,2,3,4,5] pst.
Map can be defined as shown here −
void main() { var mapping = { id : 1, name : Dart }; print(mapping); }
Dynamic − If the variable type is not defined, then its default type is dynamic. The following example illustrates the dynamic type variable −
void main() { dynamic name = "Dart"; print(name); }
Decision Making and Loops
A decision making block evaluates a condition before the instructions are executed. Dart supports If, If..else and switch statements.
Loops are used to repeat a block of code until a specific condition is met. Dart supports for, for..in , while and do..while loops.
Let us understand a simple example about the usage of control statements and loops −
void main() { for( var i = 1 ; i <= 10; i++ ) { if(i%2==0) { print(i); } } }
The above code prints the even numbers from 1 to 10.
Functions
A function is a group of statements that together performs a specific task. Let us look into a simple function in Dart as shown here −
void main() { add(3,4); } void add(int a,int b) { int c; c = a+b; print(c); }
The above function adds two values and produces 7 as the output.
Object Oriented Programming
Dart is an object-oriented language. It supports object-oriented programming features pke classes, interfaces, etc.
A class is a blueprint for creating objects. A class definition includes the following −
Fields
Getters and setters
Constructors
Functions
Now, let us create a simple class using the above definitions −
class Employee { String name; //getter method String get emp_name { return name; } //setter method void set emp_name(String name) { this.name = name; } //function definition void result() { print(name); } } void main() { //object creation Employee emp = new Employee(); emp.name = "employee1"; emp.result(); //function call }
Flutter - Introduction to Widgets
As we learned in the earper chapter, widgets are everything in Flutter framework. We have already learned how to create new widgets in previous chapters.
In this chapter, let us understand the actual concept behind creating the widgets and the different type of widgets available in Flutter framework.
Let us check the Hello World apppcation’s MyHomePage widget. The code for this purpose is as given below −
class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text(this.title), ), body: Center(child: Text( Hello World ,)), ); } }
Here, we have created a new widget by extending StatelessWidget.
Note that the StatelessWidget only requires a single method build to be implemented in its derived class. The build method gets the context environment necessary to build the widgets through BuildContext parameter and returns the widget it builds.
In the code, we have used title as one of the constructor argument and also used Key as another argument. The title is used to display the title and Key is used to identify the widget in the build environment.
Here, the build method calls the build method of Scaffold, which in turn calls the build method of AppBar and Center to build its user interface.
Finally, Center build method calls Text build method.
For a better understanding, the visual representation of the same is given below −
![Visual Representation](/flutter/images/visual_representation.jpg)
Widget Build Visuapzation
In Flutter, widgets can be grouped into multiple categories based on their features, as psted below −
Platform specific widgets
Layout widgets
State maintenance widgets
Platform independent / basic widgets
Let us discuss each of them in detail now.
Platform specific widgets
Flutter has widgets specific to a particular platform - Android or iOS.
Android specific widgets are designed in accordance with Material design guidepne by Android OS. Android specific widgets are called as Material widgets.
iOS specific widgets are designed in accordance with Human Interface Guidepnes by Apple and they are called as Cupertino widgets.
Some of the most used material widgets are as follows −
Scaffold
AppBar
BottomNavigationBar
TabBar
TabBarView
ListTile
RaisedButton
FloatingActionButton
FlatButton
IconButton
DropdownButton
PopupMenuButton
ButtonBar
TextField
Checkbox
Radio
Switch
Spder
Date & Time Pickers
SimpleDialog
AlertDialog
Some of the most used Cupertino widgets are as follows −
CupertinoButton
CupertinoPicker
CupertinoDatePicker
CupertinoTimerPicker
CupertinoNavigationBar
CupertinoTabBar
CupertinoTabScaffold
CupertinoTabView
CupertinoTextField
CupertinoDialog
CupertinoDialogAction
CupertinoFullscreenDialogTransition
CupertinoPageScaffold
CupertinoPageTransition
CupertinoActionSheet
CupertinoActivityIndicator
CupertinoAlertDialog
CupertinoPopupSurface
CupertinoSpder
Layout widgets
In Flutter, a widget can be created by composing one or more widgets. To compose multiple widgets into a single widget, Flutter provides large number of widgets with layout feature. For example, the child widget can be centered using Center widget.
Some of the popular layout widgets are as follows −
Container − A rectangular box decorated using BoxDecoration widgets with background, border and shadow.
Center − Center its child widget.
Row − Arrange its children in the horizontal direction.
Column − Arrange its children in the vertical direction.
Stack − Arrange one above the another.
We will check the layout widgets in detail in the upcoming Introduction to layout widgets chapter.
State maintenance widgets
In Flutter, all widgets are either derived from StatelessWidget or StatefulWidget.
Widget derived from StatelessWidget does not have any state information but it may contain widget derived from StatefulWidget. The dynamic nature of the apppcation is through interactive behavior of the widgets and the state changes during interaction. For example, tapping a counter button will increase / decrease the internal state of the counter by one and reactive nature of the Flutter widget will auto re-render the widget using new state information.
We will learn the concept of StatefulWidget widgets in detail in the upcoming State management chapter.
Platform independent / basic widgets
Flutter provides large number of basic widgets to create simple as well as complex user interface in a platform independent manner. Let us see some of the basic widgets in this chapter.
Text
Text widget is used to display a piece of string. The style of the string can be set by using style property and TextStyle class. The sample code for this purpose is as follows −
Text( Hello World! , style: TextStyle(fontWeight: FontWeight.bold))
Text widget has a special constructor, Text.rich, which accepts the child of type TextSpan to specify the string with different style. TextSpan widget is recursive in nature and it accepts TextSpan as its children. The sample code for this purpose is as follows −
Text.rich( TextSpan( children: <TextSpan>[ TextSpan(text: "Hello ", style: TextStyle(fontStyle: FontStyle.itapc)), TextSpan(text: "World", style: TextStyle(fontWeight: FontWeight.bold)), ], ), )
The most important properties of the Text widget are as follows −
maxLines, int − Maximum number of pnes to show
overflow, TextOverFlow − Specify how visual overflow is handled using TextOverFlow class
style, TextStyle − Specify the style of the string using TextStyle class
textApgn, TextApgn − Apgnment of the text pke right, left, justify, etc., using TextApgn class
textDirection, TextDirection − Direction of text to flow, either left-to-right or right-to-left
Image
Image widget is used to display an image in the apppcation. Image widget provides different constructors to load images from multiple sources and they are as follows −
Image − Generic image loader using ImageProvider
Image.asset − Load image from flutter project’s assets
Image.file − Load image from system folder
Image.memory − Load image from memory
Image.Network − Load image from network
The easiest option to load and display an image in Flutter is by including the image as assets of the apppcation and load it into the widget on demand.
Create a folder, assets in the project folder and place the necessary images.
Specify the assets in the pubspec.yaml as shown below −
flutter: assets: - assets/smiley.png
Now, load and display the image in the apppcation.
Image.asset( assets/smiley.png )
The complete source code of MyHomePage widget of the hello world apppcation and the result is as shown below −.
class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.title), ), body: Center( child: Image.asset("assets/smiley.png")), ); } }
The loaded image is as shown below −
![Hello World Apppcation Output](/flutter/images/hello_world_apppcation_output.jpg)
The most important properties of the Image widget are as follows −
image, ImageProvider − Actual image to load
width, double − Width of the image
height, double − Height of the image
apgnment, ApgnmentGeometry − How to apgn the image within its bounds
Icon
Icon widget is used to display a glyph from a font described in IconData class. The code to load a simple email icon is as follows −
Icon(Icons.email)
The complete source code to apply it in hello world apppcation is as follows −
class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text(this.title),), body: Center( child: Icon(Icons.email)), ); } }
The loaded icon is as shown below −
![Homepage](/flutter/images/homepage.jpg)
Flutter - Introduction to Layouts
Since the core concept of Flutter is Everything is widget, Flutter incorporates a user interface layout functionapty into the widgets itself. Flutter provides quite a lot of specially designed widgets pke Container, Center, Apgn, etc., only for the purpose of laying out the user interface. Widgets build by composing other widgets normally use layout widgets. Let use learn the Flutter layout concept in this chapter.
Type of Layout Widgets
Layout widgets can be grouped into two distinct category based on its child −
Widget supporting a single child
Widget supporting multiple child
Let us learn both type of widgets and its functionapty in the upcoming sections.
Single Child Widgets
In this category, widgets will have only one widget as its child and every widget will have a special layout functionapty.
For example, Center widget just centers it child widget with respect to its parent widget and Container widget provides complete flexibipty to place it child at any given place inside it using different option pke padding, decoration, etc.,
Single child widgets are great options to create high quapty widget having single functionapty such as button, label, etc.,
The code to create a simple button using Container widget is as follows −
class MyButton extends StatelessWidget { MyButton({Key key}) : super(key: key); @override Widget build(BuildContext context) { return Container( decoration: const BoxDecoration( border: Border( top: BorderSide(width: 1.0, color: Color(0xFFFFFFFFFF)), left: BorderSide(width: 1.0, color: Color(0xFFFFFFFFFF)), right: BorderSide(width: 1.0, color: Color(0xFFFF000000)), bottom: BorderSide(width: 1.0, color: Color(0xFFFF000000)), ), ), child: Container( padding: const EdgeInsets.symmetric(horizontal: 20.0, vertical: 2.0), decoration: const BoxDecoration( border: Border( top: BorderSide(width: 1.0, color: Color(0xFFFFDFDFDF)), left: BorderSide(width: 1.0, color: Color(0xFFFFDFDFDF)), right: BorderSide(width: 1.0, color: Color(0xFFFF7F7F7F)), bottom: BorderSide(width: 1.0, color: Color(0xFFFF7F7F7F)), ), color: Colors.grey, ), child: const Text( OK ,textApgn: TextApgn.center, style: TextStyle(color: Colors.black) ), ), ); } }
Here, we have used two widgets – a Container widget and a Text widget. The result of the widget is as a custom button as shown below −
![OK](/flutter/images/ok.jpg)
Let us check some of the most important single child layout widgets provided by Flutter −
Padding − Used to arrange its child widget by the given padding. Here, padding can be provided by EdgeInsets class.
Apgn − Apgn its child widget within itself using the value of apgnment property. The value for apgnment property can be provided by FractionalOffset class. The FractionalOffset class specifies the offsets in terms of a distance from the top left.
Some of the possible values of offsets are as follows −
FractionalOffset(1.0, 0.0) represents the top right.
FractionalOffset(0.0, 1.0) represents the bottom left.
A sample code about offsets is shown below −
Center( child: Container( height: 100.0, width: 100.0, color: Colors.yellow, child: Apgn( apgnment: FractionalOffset(0.2, 0.6), child: Container( height: 40.0, width: 40.0, color: Colors.red, ), ), ), )
FittedBox − It scales the child widget and then positions it according to the specified fit.
AspectRatio − It attempts to size the child widget to the specified aspect ratio
ConstrainedBox
Basepne
FractinallySizedBox
IntrinsicHeight
IntrinsicWidth
LiimitedBox
OffStage
OverflowBox
SizedBox
SizedOverflowBox
Transform
CustomSingleChildLayout
Our hello world apppcation is using material based layout widgets to design the home page. Let us modify our hello world apppcation to build the home page using basic layout widgets as specified below −
Container − Generic, single child, box based container widget with apgnment, padding, border and margin along with rich stypng features.
Center − Simple, Single child container widget, which centers its child widget.
The modified code of the MyHomePage and MyApp widget is as below −
class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MyHomePage(title: "Hello World demo app"); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Container( decoration: BoxDecoration(color: Colors.white,), padding: EdgeInsets.all(25), child: Center( child:Text( Hello World , style: TextStyle( color: Colors.black, letterSpacing: 0.5, fontSize: 20, ), textDirection: TextDirection.ltr, ), ) ); } }
Here,
Container widget is the top level or root widget. Container is configured using decoration and padding property to layout its content.
BoxDecoration has many properties pke color, border, etc., to decorate the Container widget and here, color is used to set the color of the container.
padding of the Container widget is set by using dgeInsets class, which provides the option to specify the padding value.
Center is the child widget of the Container widget. Again, Text is the child of the Center widget. Text is used to show message and Center is used to center the text message with respect to the parent widget, Container.
The final result of the code given above is a layout sample as shown below −
![Final Result](/flutter/images/final_result.jpg)
Multiple Child Widgets
In this category, a given widget will have more than one child widgets and the layout of each widget is unique.
For example, Row widget allows the laying out of its children in horizontal direction, whereas Column widget allows laying out of its children in vertical direction. By composing Row and Column, widget with any level of complexity can be built.
Let us learn some of the frequently used widgets in this section.
Row − Allows to arrange its children in a horizontal manner.
Column − Allows to arrange its children in a vertical manner.
ListView − Allows to arrange its children as pst.
GridView − Allows to arrange its children as gallery.
Expanded − Used to make the children of Row and Column widget to occupy the maximum possible area.
Table − Table based widget.
Flow − Flow based widget.
Stack − Stack based widget.
Advanced Layout Apppcation
In this section, let us learn how to create a complex user interface of product psting with custom design using both single and multiple child layout widgets.
For this purpose, follow the sequence given below −
Create a new Flutter apppcation in Android studio, product_layout_app.
Replace the main.dart code with folowing code −
import package:flutter/material.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { // This widget is the root of your apppcation. @override Widget build(BuildContext context) { return MaterialApp( title: Flutter Demo , theme: ThemeData( primarySwatch: Colors.blue,), home: MyHomePage(title: Product layout demo home page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text(this.title),), body: Center(child: Text( Hello World , )), ); } }
Here,
We have created MyHomePage widget by extending StatelessWidget instead of default StatefulWidget and then removed the relevant code.
Now, create a new widget, ProductBox according to the specified design as shown below −
![ProductBox](/flutter/images/productbox.jpg)
The code for the ProductBox is as follows.
class ProductBox extends StatelessWidget { ProductBox({Key key, this.name, this.description, this.price, this.image}) : super(key: key); final String name; final String description; final int price; final String image; Widget build(BuildContext context) { return Container( padding: EdgeInsets.all(2), height: 120, child: Card( child: Row( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Image.asset("assets/appimages/" +image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text(this.name, style: TextStyle(fontWeight: FontWeight.bold)), Text(this.description), Text("Price: " + this.price.toString()), ], ) ) ) ] ) ) ); } }
Please observe the following in the code −
ProductBox has used four arguments as specified below −
name - Product name
description - Product description
price - Price of the product
image - Image of the product
ProductBox uses seven build-in widgets as specified below −
Container
Expanded
Row
Column
Card
Text
Image
ProductBox is designed using the above mentioned widget. The arrangement or hierarchy of the widget is specified in the diagram shown below −
![Hierarchy of the widget](/flutter/images/hierarchy_of_widget.jpg)
Now, place some dummy image (see below) for product information in the assets folder of the apppcation and configure the assets folder in the pubspec.yaml file as shown below −
assets: - assets/appimages/floppy.png - assets/appimages/iphone.png - assets/appimages/laptop.png - assets/appimages/pendrive.png - assets/appimages/pixel.png - assets/appimages/tablet.png
![iphone](/flutter/images/iphone.jpg)
iPhone.png
![Pixel](/flutter/images/pixel.jpg)
Pixel.png
![Laptop](/flutter/images/laptop.jpg)
Laptop.png
![Tablet](/flutter/images/tablet.jpg)
Tablet.png
![Pendrive](/flutter/images/pendrive.jpg)
Pendrive.png
![Floppy Disk](/flutter/images/floppydisk.jpg)
Floppy.png
Finally, Use the ProductBox widget in the MyHomePage widget as specified below −
class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title:Text("Product Listing")), body: ListView( shrinkWrap: true, padding: const EdgeInsets.fromLTRB(2.0, 10.0, 2.0, 10.0), children: <Widget> [ ProductBox( name: "iPhone", description: "iPhone is the stypst phone ever", price: 1000, image: "iphone.png" ), ProductBox( name: "Pixel", description: "Pixel is the most featureful phone ever", price: 800, image: "pixel.png" ), ProductBox( name: "Laptop", description: "Laptop is most productive development tool", price: 2000, image: "laptop.png" ), ProductBox( name: "Tablet", description: "Tablet is the most useful device ever for meeting", price: 1500, image: "tablet.png" ), ProductBox( name: "Pendrive", description: "Pendrive is useful storage medium", price: 100, image: "pendrive.png" ), ProductBox( name: "Floppy Drive", description: "Floppy drive is useful rescue storage medium", price: 20, image: "floppy.png" ), ], ) ); } }
Here,we have used ProductBox as children of ListView widget.
The complete code (main.dart) of the product layout apppcation (product_layout_app) is as follows −
import package:flutter/material.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { // This widget is the root of your apppcation. @override Widget build(BuildContext context) { return MaterialApp( title: Flutter Demo , theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage(title: Product layout demo home page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text("Product Listing")), body: ListView( shrinkWrap: true, padding: const EdgeInsets.fromLTRB(2.0, 10.0, 2.0, 10.0), children: <Widget>[ ProductBox( name: "iPhone", description: "iPhone is the stypst phone ever", price: 1000, image: "iphone.png" ), ProductBox( name: "Pixel", description: "Pixel is the most featureful phone ever", price: 800, image: "pixel.png" ), ProductBox( name: "Laptop", description: "Laptop is most productive development tool", price: 2000, image: "laptop.png" ), ProductBox( name: "Tablet", description: "Tablet is the most useful device ever for meeting", price: 1500, image: "tablet.png" ), ProductBox( name: "Pendrive", description: "Pendrive is useful storage medium", price: 100, image: "pendrive.png" ), ProductBox( name: "Floppy Drive", description: "Floppy drive is useful rescue storage medium", price: 20, image: "floppy.png" ), ], ) ); } } class ProductBox extends StatelessWidget { ProductBox({Key key, this.name, this.description, this.price, this.image}) : super(key: key); final String name; final String description; final int price; final String image; Widget build(BuildContext context) { return Container( padding: EdgeInsets.all(2), height: 120, child: Card( child: Row( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Image.asset("assets/appimages/" + image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text( this.name, style: TextStyle( fontWeight: FontWeight.bold ) ), Text(this.description), Text( "Price: " + this.price.toString() ), ], ) ) ) ] ) ) ); } }
The final output of the apppcation is as follows −
![Product Listing](/flutter/images/product_psting.jpg)
Flutter - Introduction to Gestures
Gestures are primarily a way for a user to interact with a mobile (or any touch based device) apppcation. Gestures are generally defined as any physical action / movement of a user in the intention of activating a specific control of the mobile device. Gestures are as simple as tapping the screen of the mobile device to more complex actions used in gaming apppcations.
Some of the widely used gestures are mentioned here −
Tap − Touching the surface of the device with fingertip for a short period and then releasing the fingertip.
Double Tap − Tapping twice in a short time.
Drag − Touching the surface of the device with fingertip and then moving the fingertip in a steady manner and then finally releasing the fingertip.
Fpck − Similar to dragging, but doing it in a speeder way.
Pinch − Pinching the surface of the device using two fingers.
Spread/Zoom − Opposite of pinching.
Panning − Touching the surface of the device with fingertip and moving it in any direction without releasing the fingertip.
Flutter provides an excellent support for all type of gestures through its exclusive widget, GestureDetector. GestureDetector is a non-visual widget primarily used for detecting the user’s gesture. To identify a gesture targeted on a widget, the widget can be placed inside GestureDetector widget. GestureDetector will capture the gesture and dispatch multiple events based on the gesture.
Some of the gestures and the corresponding events are given below −
Tap
onTapDown
onTapUp
onTap
onTapCancel
Double tap
onDoubleTap
Long press
onLongPress
Vertical drag
onVerticalDragStart
onVerticalDragUpdate
onVerticalDragEnd
Horizontal drag
onHorizontalDragStart
onHorizontalDragUpdate
onHorizontalDragEnd
Pan
onPanStart
onPanUpdate
onPanEnd
Now, let us modify the hello world apppcation to include gesture detection feature and try to understand the concept.
Change the body content of the MyHomePage widget as shown below −
body: Center( child: GestureDetector( onTap: () { _showDialog(context); }, child: Text( Hello World , ) ) ),
Observe that here we have placed the GestureDetector widget above the Text widget in the widget hierarchy, captured the onTap event and then finally shown a dialog window.
Implement the *_showDialog* function to present a dialog when user tabs the hello world message. It uses the generic showDialog and AlertDialog widget to create a new dialog widget. The code is shown below −
// user defined function void _showDialog(BuildContext context) { // flutter defined function showDialog( context: context, builder: (BuildContext context) { // return object of type Dialog return AlertDialog( title: new Text("Message"), content: new Text("Hello World"), actions: <Widget>[ new FlatButton( child: new Text("Close"), onPressed: () { Navigator.of(context).pop(); }, ), ], ); }, ); }
The apppcation will reload in the device using Hot Reload feature. Now, simply cpck the message, Hello World and it will show the dialog as below −
![Hot Reload Features](/flutter/images/hot_reload_feature.jpg)
Now, close the dialog by cpcking the close option in the dialog.
The complete code (main.dart) is as follows −
import package:flutter/material.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { // This widget is the root of your apppcation. @override Widget build(BuildContext context) { return MaterialApp( title: Hello World Demo Apppcation , theme: ThemeData( primarySwatch: Colors.blue,), home: MyHomePage(title: Home page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; // user defined function void _showDialog(BuildContext context) { // flutter defined function showDialog( context: context, builder: (BuildContext context) { // return object of type Dialog return AlertDialog( title: new Text("Message"), content: new Text("Hello World"), actions: <Widget>[ new FlatButton( child: new Text("Close"), onPressed: () { Navigator.of(context).pop(); }, ), ], ); }, ); } @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text(this.title),), body: Center( child: GestureDetector( onTap: () { _showDialog(context); }, child: Text( Hello World , ) ) ), ); } }
Finally, Flutter also provides a low-level gesture detection mechanism through Listener widget. It will detect all user interactions and then dispatches the following events −
PointerDownEvent
PointerMoveEvent
PointerUpEvent
PointerCancelEvent
Flutter also provides a small set of widgets to do specific as well as advanced gestures. The widgets are psted below −
Dismissible − Supports fpck gesture to dismiss the widget.
Draggable − Supports drag gesture to move the widget.
LongPressDraggable − Supports drag gesture to move a widget, when its parent widget is also draggable.
DragTarget − Accepts any Draggable widget
IgnorePointer − Hides the widget and its children from the gesture detection process.
AbsorbPointer − Stops the gesture detection process itself and so any overlapping widget also can not able to participate in the gesture detection process and hence, no event is raised.
Scrollable − Support scrolpng of the content available inside the widget.
Flutter - State Management
Managing state in an apppcation is one of the most important and necessary process in the pfe cycle of an apppcation.
Let us consider a simple shopping cart apppcation.
User will login using their credentials into the apppcation.
Once user is logged in, the apppcation should persist the logged in user detail in all the screen.
Again, when the user selects a product and saved into a cart, the cart information should persist between the pages until the user checked out the cart.
User and their cart information at any instance is called the state of the apppcation at that instance.
A state management can be spanided into two categories based on the duration the particular state lasts in an apppcation.
− Last for a few seconds pke the current state of an animation or a single page pke current rating of a product. Flutter supports its through StatefulWidget.
− Last for entire apppcation pke logged in user details, cart information, etc., Flutter supports its through scoped_model.
Navigation and Routing
In any apppcation, navigating from one page / screen to another defines the work flow of the apppcation. The way that the navigation of an apppcation is handled is called Routing. Flutter provides a basic routing class – MaterialPageRoute and two methods - Navigator.push and Navigator.pop, to define the work flow of an apppcation.
MaterialPageRoute
MaterialPageRoute is a widget used to render its UI by replacing the entire screen with a platform specific animation.
MaterialPageRoute(builder: (context) => Widget())
Here, builder will accepts a function to build its content by supppng the current context of the apppcation.
Navigation.push
Navigation.push is used to navigate to new screen using MaterialPageRoute widget.
Navigator.push( context, MaterialPageRoute(builder: (context) => Widget()), );
Navigation.pop
Navigation.pop is used to navigate to previous screen.
Navigator.pop(context);
Let us create a new apppcation to better understand the navigation concept.
Create a new Flutter apppcation in Android studio, product_nav_app
Copy the assets folder from product_nav_app to product_state_app and add assets inside the pubspec.yaml file.
flutter: assets: - assets/appimages/floppy.png - assets/appimages/iphone.png - assets/appimages/laptop.png - assets/appimages/pendrive.png - assets/appimages/pixel.png - assets/appimages/tablet.png
Replace the default startup code (main.dart) with our startup code.
import package:flutter/material.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { // This widget is the root of your apppcation. @override Widget build(BuildContext context) { return MaterialApp( title: Flutter Demo , theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage( title: Product state demo home page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.title), ), body: Center( child: Text( Hello World ,) ), ); } }
Let us create a Product class to organize the product information.
class Product { final String name; final String description; final int price; final String image; Product(this.name, this.description, this.price, this.image); }
Let us write a method getProducts in the Product class to generate our dummy product records.
static List<Product> getProducts() { List<Product> items = <Product>[]; items.add( Product( "Pixel", "Pixel is the most feature-full phone ever", 800, "pixel.png" ) ); items.add( Product( "Laptop", "Laptop is most productive development tool", 2000, " laptop.png" ) ); items.add( Product( "Tablet", "Tablet is the most useful device ever for meeting", 1500, "tablet.png" ) ); items.add( Product( "Pendrive", "Pendrive is useful storage medium", 100, "pendrive.png" ) ); items.add( Product( "Floppy Drive", "Floppy drive is useful rescue storage medium", 20, "floppy.png" ) ); return items; } import product.dart in main.dart import Product.dart ;
Let us include our new widget, RatingBox.
class RatingBox extends StatefulWidget { @override _RatingBoxState createState() =>_RatingBoxState(); } class _RatingBoxState extends State<RatingBox> { int _rating = 0; void _setRatingAsOne() { setState(() { _rating = 1; }); } void _setRatingAsTwo() { setState(() { _rating = 2; }); } void _setRatingAsThree() { setState(() { _rating = 3; }); } Widget build(BuildContext context) { double _size = 20; print(_rating); return Row( mainAxisApgnment: MainAxisApgnment.end, crossAxisApgnment: CrossAxisApgnment.end, mainAxisSize: MainAxisSize.max, children: <Widget>[ Container( padding: EdgeInsets.all(0), child: IconButton( icon: ( _rating >= 1? Icon( Icons.star, size: _size, ) : Icon( Icons.star_border, size: _size, ) ), color: Colors.red[500], onPressed: _setRatingAsOne, iconSize: _size, ), ), Container( padding: EdgeInsets.all(0), child: IconButton( icon: ( _rating >= 2? Icon( Icons.star, size: _size, ) : Icon( Icons.star_border, size: _size, ) ), color: Colors.red[500], onPressed: _setRatingAsTwo, iconSize: _size, ), ), Container( padding: EdgeInsets.all(0), child: IconButton( icon: ( _rating >= 3 ? Icon( Icons.star, size: _size, ) : Icon( Icons.star_border, size: _size, ) ), color: Colors.red[500], onPressed: _setRatingAsThree, iconSize: _size, ), ), ], ); } }
Let us modify our ProductBox widget to work with our new Product class.
class ProductBox extends StatelessWidget { ProductBox({Key key, this.item}) : super(key: key); final Product item; Widget build(BuildContext context) { return Container( padding: EdgeInsets.all(2), height: 140, child: Card( child: Row( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Image.asset("assets/appimages/" + this.item.image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text(this.item.name, style: TextStyle(fontWeight: FontWeight.bold)), Text(this.item.description), Text("Price: " + this.item.price.toString()), RatingBox(), ], ) ) ) ] ), ) ); } }
Let us rewrite our MyHomePage widget to work with Product model and to pst all products using ListView.
class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; final items = Product.getProducts(); @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text("Product Navigation")), body: ListView.builder( itemCount: items.length, itemBuilder: (context, index) { return GestureDetector( child: ProductBox(item: items[index]), onTap: () { Navigator.push( context, MaterialPageRoute( builder: (context) => ProductPage(item: items[index]), ), ); }, ); }, )); } }
Here, we have used MaterialPageRoute to navigate to product details page.
Now, let us add ProductPage to show the product details.
class ProductPage extends StatelessWidget { ProductPage({Key key, this.item}) : super(key: key); final Product item; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.item.name), ), body: Center( child: Container( padding: EdgeInsets.all(0), child: Column( mainAxisApgnment: MainAxisApgnment.start, crossAxisApgnment: CrossAxisApgnment.start, children: <Widget>[ Image.asset("assets/appimages/" + this.item.image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text( this.item.name, style: TextStyle( fontWeight: FontWeight.bold ) ), Text(this.item.description), Text("Price: " + this.item.price.toString()), RatingBox(), ], ) ) ) ] ), ), ), ); } }
The complete code of the apppcation is as follows −
import package:flutter/material.dart ; void main() => runApp(MyApp()); class Product { final String name; final String description; final int price; final String image; Product(this.name, this.description, this.price, this.image); static List<Product> getProducts() { List<Product> items = <Product>[]; items.add( Product( "Pixel", "Pixel is the most featureful phone ever", 800, "pixel.png" ) ); items.add( Product( "Laptop", "Laptop is most productive development tool", 2000, "laptop.png" ) ); items.add( Product( "Tablet", "Tablet is the most useful device ever for meeting", 1500, "tablet.png" ) ); items.add( Product( "Pendrive", "iPhone is the stypst phone ever", 100, "pendrive.png" ) ); items.add( Product( "Floppy Drive", "iPhone is the stypst phone ever", 20, "floppy.png" ) ); items.add( Product( "iPhone", "iPhone is the stypst phone ever", 1000, "iphone.png" ) ); return items; } } class MyApp extends StatelessWidget { // This widget is the root of your apppcation. @override Widget build(BuildContext context) { return MaterialApp( title: Flutter Demo , theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage(title: Product Navigation demo home page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; final items = Product.getProducts(); @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text("Product Navigation")), body: ListView.builder( itemCount: items.length, itemBuilder: (context, index) { return GestureDetector( child: ProductBox(item: items[index]), onTap: () { Navigator.push( context, MaterialPageRoute( builder: (context) => ProductPage(item: items[index]), ), ); }, ); }, ) ); } } class ProductPage extends StatelessWidget { ProductPage({Key key, this.item}) : super(key: key); final Product item; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.item.name), ), body: Center( child: Container( padding: EdgeInsets.all(0), child: Column( mainAxisApgnment: MainAxisApgnment.start, crossAxisApgnment: CrossAxisApgnment.start, children: <Widget>[ Image.asset("assets/appimages/" + this.item.image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text(this.item.name, style: TextStyle(fontWeight: FontWeight.bold)), Text(this.item.description), Text("Price: " + this.item.price.toString()), RatingBox(), ], ) ) ) ] ), ), ), ); } } class RatingBox extends StatefulWidget { @override _RatingBoxState createState() => _RatingBoxState(); } class _RatingBoxState extends State<RatingBox> { int _rating = 0; void _setRatingAsOne() { setState(() { _rating = 1; }); } void _setRatingAsTwo() { setState(() { _rating = 2; }); } void _setRatingAsThree() { setState(() { _rating = 3; }); } Widget build(BuildContext context) { double _size = 20; print(_rating); return Row( mainAxisApgnment: MainAxisApgnment.end, crossAxisApgnment: CrossAxisApgnment.end, mainAxisSize: MainAxisSize.max, children: <Widget>[ Container( padding: EdgeInsets.all(0), child: IconButton( icon: ( _rating >= 1 ? Icon( Icons.star, size: _size, ) : Icon( Icons.star_border, size: _size, ) ), color: Colors.red[500], onPressed: _setRatingAsOne, iconSize: _size, ), ), Container( padding: EdgeInsets.all(0), child: IconButton( icon: ( _rating >= 2 ? Icon( Icons.star, size: _size, ) : Icon( Icons.star_border, size: _size, ) ), color: Colors.red[500], onPressed: _setRatingAsTwo, iconSize: _size, ), ), Container( padding: EdgeInsets.all(0), child: IconButton( icon: ( _rating >= 3 ? Icon( Icons.star, size: _size, ) : Icon( Icons.star_border, size: _size, ) ), color: Colors.red[500], onPressed: _setRatingAsThree, iconSize: _size, ), ), ], ); } } class ProductBox extends StatelessWidget { ProductBox({Key key, this.item}) : super(key: key); final Product item; Widget build(BuildContext context) { return Container( padding: EdgeInsets.all(2), height: 140, child: Card( child: Row( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Image.asset("assets/appimages/" + this.item.image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text(this.item.name, style: TextStyle(fontWeight: FontWeight.bold)), Text(this.item.description), Text("Price: " + this.item.price.toString()), RatingBox(), ], ) ) ) ] ), ) ); } }
Run the apppcation and cpck any one of the product item. It will show the relevant details page. We can move to home page by cpcking back button. The product pst page and product details page of the apppcation are shown as follows −
![Product Navigation](/flutter/images/product_navigation.jpg)
![Pixel1](/flutter/images/pixel1.jpg)
Flutter - Animation
Animation is a complex procedure in any mobile apppcation. In spite of its complexity, Animation enhances the user experience to a new level and provides a rich user interaction. Due to its richness, animation becomes an integral part of modern mobile apppcation. Flutter framework recognizes the importance of Animation and provides a simple and intuitive framework to develop all types of animations.
Introduction
Animation is a process of showing a series of images / picture in a particular order within a specific duration to give an illusion of movement. The most important aspects of the animation are as follows −
Animation have two distinct values: Start value and End value. The animation starts from Start value and goes through a series of intermediate values and finally ends at End values. For example, to animate a widget to fade away, the initial value will be the full opacity and the final value will be the zero opacity.
The intermediate values may be pnear or non-pnear (curve) in nature and it can be configured. Understand that the animation works as it is configured. Each configuration provides a different feel to the animation. For example, fading a widget will be pnear in nature whereas bouncing of a ball will be non-pnear in nature.
The duration of the animation process affects the speed (slowness or fastness) of the animation.
The abipty to control the animation process pke starting the animation, stopping the animation, repeating the animation to set number of times, reversing the process of animation, etc.,
In Flutter, animation system does not do any real animation. Instead, it provides only the values required at every frame to render the images.
Animation Based Classes
Flutter animation system is based on Animation objects. The core animation classes and its usage are as follows −
Animation
Generates interpolated values between two numbers over a certain duration. The most common Animation classes are −
Animation<double> − interpolate values between two decimal number
Animation<Color> − interpolate colors between two color
Animation<Size> − interpolate sizes between two size
AnimationController − Special Animation object to control the animation itself. It generates new values whenever the apppcation is ready for a new frame. It supports pnear based animation and the value starts from 0.0 to 1.0
controller = AnimationController(duration: const Duration(seconds: 2), vsync: this);
Here, controller controls the animation and duration option controls the duration of the animation process. vsync is a special option used to optimize the resource used in the animation.
CurvedAnimation
Similar to AnimationController but supports non-pnear animation. CurvedAnimation can be used along with Animation object as below −
controller = AnimationController(duration: const Duration(seconds: 2), vsync: this); animation = CurvedAnimation(parent: controller, curve: Curves.easeIn)
Tween<T>
Derived from Animatable<T> and used to generate numbers between any two numbers other than 0 and 1. It can be used along with Animation object by using animate method and passing actual Animation object.
AnimationController controller = AnimationController( duration: const Duration(milpseconds: 1000), vsync: this); Animation<int> customTween = IntTween( begin: 0, end: 255).animate(controller);
Tween can also used along with CurvedAnimation as below −
AnimationController controller = AnimationController( duration: const Duration(milpseconds: 500), vsync: this); final Animation curve = CurvedAnimation(parent: controller, curve: Curves.easeOut); Animation<int> customTween = IntTween(begin: 0, end: 255).animate(curve);
Here, controller is the actual animation controller. curve provides the type of non-pnearity and the customTween provides custom range from 0 to 255.
Work flow of the Flutter Animation
The work flow of the animation is as follows −
Define and start the animation controller in the initState of the StatefulWidget.
AnimationController(duration: const Duration(seconds: 2), vsync: this); animation = Tween<double>(begin: 0, end: 300).animate(controller); controller.forward();
Add animation based pstener, addListener to change the state of the widget.
animation = Tween<double>(begin: 0, end: 300).animate(controller) ..addListener(() { setState(() { // The state that has changed here is the animation object’s value. }); });
Build-in widgets, AnimatedWidget and AnimatedBuilder can be used to skip this process. Both widget accepts Animation object and get current values required for the animation.
Get the animation values during the build process of the widget and then apply it for width, height or any relevant property instead of the original value.
child: Container( height: animation.value, width: animation.value, child: <Widget>, )
Working Apppcation
Let us write a simple animation based apppcation to understand the concept of animation in Flutter framework.
Create a new Flutter apppcation in Android studio, product_animation_app.
Copy the assets folder from product_nav_app to product_animation_app and add assets inside the pubspec.yaml file.
flutter: assets: - assets/appimages/floppy.png - assets/appimages/iphone.png - assets/appimages/laptop.png - assets/appimages/pendrive.png - assets/appimages/pixel.png - assets/appimages/tablet.png
Remove the default startup code (main.dart).
Add import and basic main function.
import package:flutter/material.dart ; void main() => runApp(MyApp());
Create the MyApp widget derived from StatefulWidgtet.
class MyApp extends StatefulWidget { _MyAppState createState() => _MyAppState(); }
Create _MyAppState widget and implement initState and dispose in addition to default build method.
class _MyAppState extends State<MyApp> with SingleTickerProviderStateMixin { Animation<double> animation; AnimationController controller; @override void initState() { super.initState(); controller = AnimationController( duration: const Duration(seconds: 10), vsync: this ); animation = Tween<double>(begin: 0.0, end: 1.0).animate(controller); controller.forward(); } // This widget is the root of your apppcation. @override Widget build(BuildContext context) { controller.forward(); return MaterialApp( title: Flutter Demo , theme: ThemeData(primarySwatch: Colors.blue,), home: MyHomePage(title: Product layout demo home page , animation: animation,) ); } @override void dispose() { controller.dispose(); super.dispose(); } }
Here,
In initState method, we have created an animation controller object (controller), an animation object (animation) and started the animation using controller.forward.
In dispose method, we have disposed the animation controller object (controller).
In build method, send animation to MyHomePage widget through constructor. Now, MyHomePage widget can use the animation object to animate its content.
Now, add ProductBox widget
class ProductBox extends StatelessWidget { ProductBox({Key key, this.name, this.description, this.price, this.image}) : super(key: key); final String name; final String description; final int price; final String image; Widget build(BuildContext context) { return Container( padding: EdgeInsets.all(2), height: 140, child: Card( child: Row( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Image.asset("assets/appimages/" + image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text(this.name, style: TextStyle(fontWeight: FontWeight.bold)), Text(this.description), Text("Price: " + this.price.toString()), ], ) ) ) ] ) ) ); } }
Create a new widget, MyAnimatedWidget to do simple fade animation using opacity.
class MyAnimatedWidget extends StatelessWidget { MyAnimatedWidget({this.child, this.animation}); final Widget child; final Animation<double> animation; Widget build(BuildContext context) => Center( child: AnimatedBuilder( animation: animation, builder: (context, child) => Container( child: Opacity(opacity: animation.value, child: child), ), child: child), ); }
Here, we have used AniatedBuilder to do our animation. AnimatedBuilder is a widget which build its content while doing the animation at the same time. It accepts a animation object to get current animation value. We have used animation value, animation.value to set the opacity of the child widget. In effect, the widget will animate the child widget using opacity concept.
Finally, create the MyHomePage widget and use the animation object to animate any of its content.
class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title, this.animation}) : super(key: key); final String title; final Animation<double> animation; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text("Product Listing")),body: ListView( shrinkWrap: true, padding: const EdgeInsets.fromLTRB(2.0, 10.0, 2.0, 10.0), children: <Widget>[ FadeTransition( child: ProductBox( name: "iPhone", description: "iPhone is the stypst phone ever", price: 1000, image: "iphone.png" ), opacity: animation ), MyAnimatedWidget(child: ProductBox( name: "Pixel", description: "Pixel is the most featureful phone ever", price: 800, image: "pixel.png" ), animation: animation), ProductBox( name: "Laptop", description: "Laptop is most productive development tool", price: 2000, image: "laptop.png" ), ProductBox( name: "Tablet", description: "Tablet is the most useful device ever for meeting", price: 1500, image: "tablet.png" ), ProductBox( name: "Pendrive", description: "Pendrive is useful storage medium", price: 100, image: "pendrive.png" ), ProductBox( name: "Floppy Drive", description: "Floppy drive is useful rescue storage medium", price: 20, image: "floppy.png" ), ], ) ); } }
Here, we have used FadeAnimation and MyAnimationWidget to animate the first two items in the pst. FadeAnimation is a build-in animation class, which we used to animate its child using opacity concept.
The complete code is as follows −
import package:flutter/material.dart ; void main() => runApp(MyApp()); class MyApp extends StatefulWidget { _MyAppState createState() => _MyAppState(); } class _MyAppState extends State<MyApp> with SingleTickerProviderStateMixin { Animation<double> animation; AnimationController controller; @override void initState() { super.initState(); controller = AnimationController( duration: const Duration(seconds: 10), vsync: this); animation = Tween<double>(begin: 0.0, end: 1.0).animate(controller); controller.forward(); } // This widget is the root of your apppcation. @override Widget build(BuildContext context) { controller.forward(); return MaterialApp( title: Flutter Demo , theme: ThemeData(primarySwatch: Colors.blue,), home: MyHomePage(title: Product layout demo home page , animation: animation,) ); } @override void dispose() { controller.dispose(); super.dispose(); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title, this.animation}): super(key: key); final String title; final Animation<double> animation; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text("Product Listing")), body: ListView( shrinkWrap: true, padding: const EdgeInsets.fromLTRB(2.0, 10.0, 2.0, 10.0), children: <Widget>[ FadeTransition( child: ProductBox( name: "iPhone", description: "iPhone is the stypst phone ever", price: 1000, image: "iphone.png" ), opacity: animation ), MyAnimatedWidget( child: ProductBox( name: "Pixel", description: "Pixel is the most featureful phone ever", price: 800, image: "pixel.png" ), animation: animation ), ProductBox( name: "Laptop", description: "Laptop is most productive development tool", price: 2000, image: "laptop.png" ), ProductBox( name: "Tablet", description: "Tablet is the most useful device ever for meeting", price: 1500, image: "tablet.png" ), ProductBox( name: "Pendrive", description: "Pendrive is useful storage medium", price: 100, image: "pendrive.png" ), ProductBox( name: "Floppy Drive", description: "Floppy drive is useful rescue storage medium", price: 20, image: "floppy.png" ), ], ) ); } } class ProductBox extends StatelessWidget { ProductBox({Key key, this.name, this.description, this.price, this.image}) : super(key: key); final String name; final String description; final int price; final String image; Widget build(BuildContext context) { return Container( padding: EdgeInsets.all(2), height: 140, child: Card( child: Row( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Image.asset("assets/appimages/" + image), Expanded( child: Container( padding: EdgeInsets.all(5), child: Column( mainAxisApgnment: MainAxisApgnment.spaceEvenly, children: <Widget>[ Text( this.name, style: TextStyle( fontWeight: FontWeight.bold ) ), Text(this.description), Text( "Price: " + this.price.toString() ), ], ) ) ) ] ) ) ); } } class MyAnimatedWidget extends StatelessWidget { MyAnimatedWidget({this.child, this.animation}); final Widget child; final Animation<double> animation; Widget build(BuildContext context) => Center( child: AnimatedBuilder( animation: animation, builder: (context, child) => Container( child: Opacity(opacity: animation.value, child: child), ), child: child ), ); }
Compile and run the apppcation to see the results. The initial and final version of the apppcation is as follows −
![Initial Version](/flutter/images/initial_version.jpg)
![Final Version](/flutter/images/final_version.jpg)
Flutter - Writing Android Specific Code
Flutter provides a general framework to access platform specific feature. This enables the developer to extend the functionapty of the Flutter framework using platform specific code. Platform specific functionapty pke camera, battery level, browser, etc., can be accessed easily through the framework.
The general idea of accessing the platform specific code is through simple messaging protocol. Flutter code, Cpent and the platform code and Host binds to a common Message Channel. Cpent sends message to the Host through the Message Channel. Host pstens on the Message Channel, receives the message and does the necessary functionapty and finally, returns the result to the Cpent through Message Channel.
The platform specific code architecture is shown in the block diagram given below −
![Specific Code Architecture](/flutter/images/specific_code_architecture.jpg)
The messaging protocol uses a standard message codec (StandardMessageCodec class) that supports binary seriapzation of JSON-pke values such as numbers, strings, boolean, etc., The seriapzation and de-seriapzation works transparently between the cpent and the host.
Let us write a simple apppcation to open a browser using Android SDK and understand how
Create a new Flutter apppcation in Android studio, flutter_browser_app
Replace main.dart code with below code −
import package:flutter/material.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( title: Flutter Demo , theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage(title: Flutter Demo Home Page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.title), ), body: Center( child: RaisedButton( child: Text( Open Browser ), onPressed: null, ), ), ); } }
Here, we have created a new button to open the browser and set its onPressed method as null.
Now, import the following packages −
import dart:async ; import package:flutter/services.dart ;
Here, services.dart include the functionapty to invoke platform specific code.
Create a new message channel in the MyHomePage widget.
static const platform = const MethodChannel( flutterapp.tutorialspoint.com/browser );
Write a method, _openBrowser to invoke platform specific method, openBrowser method through message channel.
Future<void> _openBrowser() async { try { final int result = await platform.invokeMethod( openBrowser , <String, String>{ url : "https://flutter.dev" } ); } on PlatformException catch (e) { // Unable to open the browser print(e); } }
Here, we have used platform.invokeMethod to invoke openBrowser (explained in coming steps). openBrowser has an argument, url to open a specific url.
Change the value of onPressed property of the RaisedButton from null to _openBrowser.
onPressed: _openBrowser,
Open MainActivity.java (inside the android folder) and import the required pbrary −
import android.app.Activity; import android.content.Intent; import android.net.Uri; import android.os.Bundle; import io.flutter.app.FlutterActivity; import io.flutter.plugin.common.MethodCall; import io.flutter.plugin.common.MethodChannel; import io.flutter.plugin.common.MethodChannel.MethodCallHandler; import io.flutter.plugin.common.MethodChannel.Result; import io.flutter.plugins.GeneratedPluginRegistrant;
Write a method, openBrowser to open a browser
private void openBrowser(MethodCall call, Result result, String url) { Activity activity = this; if (activity == null) { result.error("ACTIVITY_NOT_AVAILABLE", "Browser cannot be opened without foreground activity", null); return; } Intent intent = new Intent(Intent.ACTION_VIEW); intent.setData(Uri.parse(url)); activity.startActivity(intent); result.success((Object) true); }
Now, set channel name in the MainActivity class −
private static final String CHANNEL = "flutterapp.tutorialspoint.com/browser";
Write android specific code to set message handpng in the onCreate method −
new MethodChannel(getFlutterView(), CHANNEL).setMethodCallHandler( new MethodCallHandler() { @Override pubpc void onMethodCall(MethodCall call, Result result) { String url = call.argument("url"); if (call.method.equals("openBrowser")) { openBrowser(call, result, url); } else { result.notImplemented(); } } });
Here, we have created a message channel using MethodChannel class and used MethodCallHandler class to handle the message. onMethodCall is the actual method responsible for calpng the correct platform specific code by the checking the message. onMethodCall method extracts the url from message and then invokes the openBrowser only when the method call is openBrowser. Otherwise, it returns notImplemented method.
The complete source code of the apppcation is as follows −
main.dart
MainActivity.java
package com.tutorialspoint.flutterapp.flutter_browser_app; import android.app.Activity; import android.content.Intent; import android.net.Uri; import android.os.Bundle; import io.flutter.app.FlutterActivity; import io.flutter.plugin.common.MethodCall; import io.flutter.plugin.common.MethodChannel.Result; import io.flutter.plugins.GeneratedPluginRegistrant; pubpc class MainActivity extends FlutterActivity { private static final String CHANNEL = "flutterapp.tutorialspoint.com/browser"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); GeneratedPluginRegistrant.registerWith(this); new MethodChannel(getFlutterView(), CHANNEL).setMethodCallHandler( new MethodCallHandler() { @Override pubpc void onMethodCall(MethodCall call, Result result) { String url = call.argument("url"); if (call.method.equals("openBrowser")) { openBrowser(call, result, url); } else { result.notImplemented(); } } } ); } private void openBrowser(MethodCall call, Result result, String url) { Activity activity = this; if (activity == null) { result.error( "ACTIVITY_NOT_AVAILABLE", "Browser cannot be opened without foreground activity", null ); return; } Intent intent = new Intent(Intent.ACTION_VIEW); intent.setData(Uri.parse(url)); activity.startActivity(intent); result.success((Object) true); } }
main.dart
import package:flutter/material.dart ; import dart:async ; import package:flutter/services.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( title: Flutter Demo , theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage( title: Flutter Demo Home Page ), ); } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; static const platform = const MethodChannel( flutterapp.tutorialspoint.com/browser ); Future<void> _openBrowser() async { try { final int result = await platform.invokeMethod( openBrowser , <String, String>{ url : "https://flutter.dev" }); } on PlatformException catch (e) { // Unable to open the browser print(e); } } @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.title), ), body: Center( child: RaisedButton( child: Text( Open Browser ), onPressed: _openBrowser, ), ), ); } }
Run the apppcation and cpck the Open Browser button and you can see that the browser is launched. The Browser app - Home page is as shown in the screenshot here −
![Flutter Demo Home Page](/flutter/images/flutter_demo_home_page.jpg)
![Productively Build Apps](/flutter/images/productively_build_apps.jpg)
Flutter - Writing IOS Specific Code
Accessing iOS specific code is similar to that on Android platform except that it uses iOS specific languages - Objective-C or Swift and iOS SDK. Otherwise, the concept is same as that of the Android platform.
Let us write the same apppcation as in the previous chapter for iOS platform as well.
Let us create a new apppcation in Android Studio (macOS), flutter_browser_ios_app
Follow steps 2 - 6 as in previous chapter.
Start XCode and cpck File → Open
Choose the xcode project under ios directory of our flutter project.
Open AppDelegate.m under Runner → Runner path. It contains the following code −
#include "AppDelegate.h" #include "GeneratedPluginRegistrant.h" @implementation AppDelegate - (BOOL)apppcation:(UIApppcation *)apppcation didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { // [GeneratedPluginRegistrant registerWithRegistry:self]; // Override point for customization after apppcation launch. return [super apppcation:apppcation didFinishLaunchingWithOptions:launchOptions]; } @end
We have added a method, openBrowser to open browser with specified url. It accepts single argument, url.
- (void)openBrowser:(NSString *)urlString { NSURL *url = [NSURL URLWithString:urlString]; UIApppcation *apppcation = [UIApppcation sharedApppcation]; [apppcation openURL:url]; }
In didFinishLaunchingWithOptions method, find the controller and set it in controller variable.
FlutterViewController* controller = (FlutterViewController*)self.window.rootViewController;
In didFinishLaunchingWithOptions method, set the browser channel as flutterapp.tutorialspoint.com/browse −
FlutterMethodChannel* browserChannel = [ FlutterMethodChannel methodChannelWithName: @"flutterapp.tutorialspoint.com/browser" binaryMessenger:controller];
Create a variable, weakSelf and set current class −
__weak typeof(self) weakSelf = self;
Now, implement setMethodCallHandler. Call openBrowser by matching call.method. Get url by invoking call.arguments and pass it while calpng openBrowser.
[browserChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) { if ([@"openBrowser" isEqualToString:call.method]) { NSString *url = call.arguments[@"url"]; [weakSelf openBrowser:url]; } else { result(FlutterMethodNotImplemented); } }];
The complete code is as follows −
#include "AppDelegate.h" #include "GeneratedPluginRegistrant.h" @implementation AppDelegate - (BOOL)apppcation:(UIApppcation *)apppcation didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { // custom code starts FlutterViewController* controller = (FlutterViewController*)self.window.rootViewController; FlutterMethodChannel* browserChannel = [ FlutterMethodChannel methodChannelWithName: @"flutterapp.tutorialspoint.com /browser" binaryMessenger:controller]; __weak typeof(self) weakSelf = self; [browserChannel setMethodCallHandler:^( FlutterMethodCall* call, FlutterResult result) { if ([@"openBrowser" isEqualToString:call.method]) { NSString *url = call.arguments[@"url"]; [weakSelf openBrowser:url]; } else { result(FlutterMethodNotImplemented); } }]; // custom code ends [GeneratedPluginRegistrant registerWithRegistry:self]; // Override point for customization after apppcation launch. return [super apppcation:apppcation didFinishLaunchingWithOptions:launchOptions]; } - (void)openBrowser:(NSString *)urlString { NSURL *url = [NSURL URLWithString:urlString]; UIApppcation *apppcation = [UIApppcation sharedApppcation]; [apppcation openURL:url]; } @end
Open project setting.
Go to Capabipties and enable Background Modes.
Add *Background fetch and Remote Notification**.
Now, run the apppcation. It works similar to Android version but the Safari browser will be opened instead of chrome.
Flutter - Introduction to Package
Dart’s way of organizing and sharing a set of functionapty is through Package. Dart Package is simply sharable pbraries or modules. In general, the Dart Package is same as that of Dart Apppcation except Dart Package does not have apppcation entry point, main.
The general structure of Package (consider a demo package, my_demo_package) is as below −
pb/src/* − Private Dart code files.
pb/my_demo_package.dart − Main Dart code file. It can be imported into an apppcation as −
import package:my_demo_package/my_demo_package.dart
Other private code file may be exported into the main code file (my_demo_package.dart), if necessary as shown below −
export src/my_private_code.dart
pb/* − Any number of Dart code files arranged in any custom folder structure. The code can be accessed as,
import package:my_demo_package/custom_folder/custom_file.dart
pubspec.yaml − Project specification, same as that of apppcation,
All Dart code files in the Package are simply Dart classes and it does not have any special requirement for a Dart code to include it in a Package.
Types of Packages
Since Dart Packages are basically a small collection of similar functionapty, it can be categorized based on its functionapty.
Dart Package
Generic Dart code, which can be used in both web and mobile environment. For example, engpsh_words is one such package which contains around 5000 words and has basic utipty functions pke nouns (pst nouns in the Engpsh), syllables (specify number of syllables in a word.
Flutter Package
Generic Dart code, which depends on Flutter framework and can be used only in mobile environment. For example, fluro is a custom router for flutter. It depends on the Flutter framework.
Flutter Plugin
Generic Dart code, which depends on Flutter framework as well as the underlying platform code (Android SDK or iOS SDK). For example, camera is a plugin to interact with device camera. It depends on the Flutter framework as well as the underlying framework to get access to camera.
Using a Dart Package
Dart Packages are hosted and pubpshed into the pve server,
Also, Flutter provides simple tool, pub to manage Dart Packages in the apppcation. The steps needed to use as Package is as follows −Include the package name and the version needed into the pubspec.yaml as shown below −
dependencies: engpsh_words: ^3.1.5
The latest version number can be found by checking the onpne server.
Install the package into the apppcation by using the following command −
flutter packages get
While developing in the Android studio, Android Studio detects any change in the pubspec.yaml and displays an Android studio package alert to the developer as shown below −
![Package Alert](/flutter/images/package_alert.jpg)
Dart Packages can be installed or updated in Android Studio using the menu options.
Import the necessary file using the command shown below and start working −
import package:engpsh_words/engpsh_words.dart ;
Use any method available in the package,
nouns.take(50).forEach(print);
Here, we have used nouns function to get and print the top 50 words.
Develop a Flutter Plugin Package
Developing a Flutter Plugin is similar to developing a Dart apppcation or Dart Package. The only exception is that the plugin is going to use System API (Android or iOS) to get the required platform specific functionapty.
As we have already learned how to access platform code in the previous chapters, let us develop a simple plugin, my_browser to understand the plugin development process. The functionapty of the my_browser plugin is to allow the apppcation to open the given website in the platform specific browser.
Start Android Studio.
Cpck File → New Flutter Project and select Flutter Plugin option.
You can see a Flutter plugin selection window as shown here −
![Flutter Plugin](/flutter/images/flutter_plugin.jpg)
Enter my_browser as project name and cpck Next.
Enter the plugin name and other details in the window as shown here −
![Configure New Flutter Plugin](/flutter/images/configure_new_flutter_plugin.jpg)
Enter company domain, flutterplugins.tutorialspoint.com in the window shown below and then cpck on Finish. It will generate a startup code to develop our new plugin.
![Package Name](/flutter/images/package_name.jpg)
Open my_browser.dart file and write a method, openBrowser to invoke platform specific openBrowser method.
Future<void> openBrowser(String urlString) async { try { final int result = await _channel.invokeMethod( openBrowser , <String, String>{ url : urlString } ); } on PlatformException catch (e) { // Unable to open the browser print(e); } }
Open MyBrowserPlugin.java file and import the following classes −
import android.app.Activity; import android.content.Intent; import android.net.Uri; import android.os.Bundle;
Here, we have to import pbrary required for opening a browser from Android.
Add new private variable mRegistrar of type Registrar in MyBrowserPlugin class.
private final Registrar mRegistrar;
Here, Registrar is used to get context information of the invoking code.
Add a constructor to set Registrar in MyBrowserPlugin class.
private MyBrowserPlugin(Registrar registrar) { this.mRegistrar = registrar; }
Change registerWith to include our new constructor in MyBrowserPlugin class.
pubpc static void registerWith(Registrar registrar) { final MethodChannel channel = new MethodChannel(registrar.messenger(), "my_browser"); MyBrowserPlugin instance = new MyBrowserPlugin(registrar); channel.setMethodCallHandler(instance); }
Change the onMethodCall to include openBrowser method in MyBrowserPlugin class.
@Override pubpc void onMethodCall(MethodCall call, Result result) { String url = call.argument("url"); if (call.method.equals("getPlatformVersion")) { result.success("Android " + android.os.Build.VERSION.RELEASE); } else if (call.method.equals("openBrowser")) { openBrowser(call, result, url); } else { result.notImplemented(); } }
Write the platform specific openBrowser method to access browser in MyBrowserPlugin class.
private void openBrowser(MethodCall call, Result result, String url) { Activity activity = mRegistrar.activity(); if (activity == null) { result.error("ACTIVITY_NOT_AVAILABLE", "Browser cannot be opened without foreground activity", null); return; } Intent intent = new Intent(Intent.ACTION_VIEW); intent.setData(Uri.parse(url)); activity.startActivity(intent); result.success((Object) true); }
The complete source code of the my_browser plugin is as follows −
my_browser.dart
import dart:async ; import package:flutter/services.dart ; class MyBrowser { static const MethodChannel _channel = const MethodChannel( my_browser ); static Future<String> get platformVersion async { final String version = await _channel.invokeMethod( getPlatformVersion ); return version; } Future<void> openBrowser(String urlString) async { try { final int result = await _channel.invokeMethod( openBrowser , <String, String>{ url : urlString}); } on PlatformException catch (e) { // Unable to open the browser print(e); } } }
MyBrowserPlugin.java
package com.tutorialspoint.flutterplugins.my_browser; import io.flutter.plugin.common.MethodCall; import io.flutter.plugin.common.MethodChannel; import io.flutter.plugin.common.MethodChannel.MethodCallHandler; import io.flutter.plugin.common.MethodChannel.Result; import io.flutter.plugin.common.PluginRegistry.Registrar; import android.app.Activity; import android.content.Intent; import android.net.Uri; import android.os.Bundle; /** MyBrowserPlugin */ pubpc class MyBrowserPlugin implements MethodCallHandler { private final Registrar mRegistrar; private MyBrowserPlugin(Registrar registrar) { this.mRegistrar = registrar; } /** Plugin registration. */ pubpc static void registerWith(Registrar registrar) { final MethodChannel channel = new MethodChannel( registrar.messenger(), "my_browser"); MyBrowserPlugin instance = new MyBrowserPlugin(registrar); channel.setMethodCallHandler(instance); } @Override pubpc void onMethodCall(MethodCall call, Result result) { String url = call.argument("url"); if (call.method.equals("getPlatformVersion")) { result.success("Android " + android.os.Build.VERSION.RELEASE); } else if (call.method.equals("openBrowser")) { openBrowser(call, result, url); } else { result.notImplemented(); } } private void openBrowser(MethodCall call, Result result, String url) { Activity activity = mRegistrar.activity(); if (activity == null) { result.error("ACTIVITY_NOT_AVAILABLE", "Browser cannot be opened without foreground activity", null); return; } Intent intent = new Intent(Intent.ACTION_VIEW); intent.setData(Uri.parse(url)); activity.startActivity(intent); result.success((Object) true); } }
Create a new project, my_browser_plugin_test to test our newly created plugin.
Open pubspec.yaml and set my_browser as a plugin dependency.
dependencies: flutter: sdk: flutter my_browser: path: ../my_browser
Android studio will alert that the pubspec.yaml is updated as shown in the Android studio package alert given below −
![Android Studio Package Alert](/flutter/images/android_studio_package_alert.jpg)
Cpck Get dependencies option. Android studio will get the package from Internet and properly configure it for the apppcation.
Open main.dart and include my_browser plugin as below −
import package:my_browser/my_browser.dart ;
Call the openBrowser function from my_browser plugin as shown below −
onPressed: () => MyBrowser().openBrowser("https://flutter.dev"),
The complete code of the main.dart is as follows −
import package:flutter/material.dart ; import package:my_browser/my_browser.dart ; void main() => runApp(MyApp()); class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( title: Flutter Demo , theme: ThemeData( primarySwatch: Colors.blue, ), home: MyHomePage( title: Flutter Demo Home Page ), );, } } class MyHomePage extends StatelessWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(this.title), ), body: Center( child: RaisedButton( child: Text( Open Browser ), onPressed: () => MyBrowser().openBrowser("https://flutter.dev"), ), ), ); } }
Run the apppcation and cpck the Open Browser button and see that the browser is launched. You can see a Browser app - Home page as shown in the screenshot shown below −
![Open Browser](/flutter/images/open_browser.jpg)
You can see a Browser app – Browser screen as shown in the screenshot shown below −
![Flutter Infrastructure](/flutter/images/flutter_infrastructure.jpg)