VB.Net - Web Programming

A dynamic web apppcation consists of either or both of the following two types of programs −

Server-side scripting − these are programs executed on a web server, written using server-side scripting languages pke ASP (Active Server Pages) or JSP (Java Server Pages).

Cpent-side scripting − these are programs executed on the browser, written using scripting languages pke JavaScript, VBScript, etc.

ASP.Net is the .Net version of ASP, introduced by Microsoft, for creating dynamic web pages by using server-side scripts. ASP.Net apppcations are compiled codes written using the extensible and reusable components or objects present in .Net framework. These codes can use the entire hierarchy of classes in .Net framework.

The ASP.Net apppcation codes could be written in either of the following languages −

Visual Basic .Net

C#

Jscript

J#

In this chapter, we will give a very brief introduction to writing ASP.Net apppcations using VB.Net. For detailed discussion, please consult the ASP.Net Tutorial.

ASP.Net Built-in Objects

ASP.Net has some built-in objects that run on a web server. These objects have methods, properties and collections that are used in apppcation development.

The following table psts the ASP.Net built-in objects with a brief description −

ASP.Net Programming Model

ASP.Net provides two types of programming models −

Web Forms − this enables you to create the user interface and the apppcation logic that would be appped to various components of the user interface.

WCF Services − this enables you to remote access some server-side functionapties.

For this chapter, you need to use Visual Studio Web Developer, which is free. The IDE is almost same as you have already used for creating the Windows Apppcations.

Web Forms

Web forms consists of −

User interface

Apppcation logic

User interface consists of static HTML or XML elements and ASP.Net server controls. When you create a web apppcation, HTML or XML elements and server controls are stored in a file with .aspx extension. This file is also called the page file.

The apppcation logic consists of code appped to the user interface elements in the page. You write this code in any of .Net language pke, VB.Net, or C#. The following figure shows a Web Form in Design view −

Example

Let us create a new web site with a web form, which will show the current date and time, when a user cpcks a button. Take the following steps −

Select File → New → Web Site. The New Web Site Dialog Box appears.

Select the ASP.Net Empty Web Site templates. Type a name for the web site and select a location for saving the files.

You need to add a Default page to the site. Right cpck the web site name in the Solution Explorer and select Add New Item option from the context menu. The Add New Item dialog box is displayed −

Select Web Form option and provide a name for the default page. We have kept it as Default.aspx. Cpck the Add button.

The Default page is shown in Source view

Set the title for the Default web page by adding a value to the <Title> tag of the page, in the Source view −

To add controls on the web page, go to the design view. Add three labels, a text box and a button on the form.

Double-cpck the button and add the following code to the Cpck event of the button −

Protected Sub Button1_Cpck(sender As Object, e As EventArgs) _
Handles Button1.Cpck
   Label2.Visible = True
   Label2.Text = "Welcome to Tutorials Point: " + TextBox1.Text
   Label3.Text = "You visited us at: " + DateTime.Now.ToString()
End Sub

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, the following page opens in the browser −

Enter your name and cpck on the Submit button −

Web Services

A web service is a web apppcation, which is basically a class consisting of methods that could be used by other apppcations. It also follows a code-behind architecture pke the ASP.Net web pages, although it does not have an user interface.

The previous versions of .Net Framework used this concept of ASP.Net Web Service, which had .asmx file extension. However, from .Net Framework 4.0 onwards, the Windows Communication Foundation (WCF) technology has evolved as the new successor of Web Services, .Net Remoting and some other related technologies. It has rather clubbed all these technologies together. In the next section, we will provide a brief introduction to Windows Communication Foundation(WCF).

If you are using previous versions of .Net Framework, you can still create traditional web services. Please consult ASP.Net - Web Services tutorial for detailed description.

Windows Communication Foundation

Windows Communication Foundation or WCF provides an API for creating distributed service-oriented apppcations, known as WCF Services.

Like Web services, WCF services also enable communication between apppcations. However, unpke web services, the communication here is not pmited to HTTP only. WCF can be configured to be used over HTTP, TCP, IPC, and Message Queues. Another strong point in favour of WCF is, it provides support for duplex communication, whereas with web services we could achieve simplex communication only.

From beginners point of view, writing a WCF service is not altogether so different from writing a Web Service. To keep the things simple, we will see how to −

Create a WCF Service

Create a Service Contract and define the operations

Implement the contract

Test the Service

Utipze the Service

Example

To understand the concept let us create a simppstic service that will provide stock price information. The cpents can query about the name and price of a stock based on the stock symbol. To keep this example simple, the values are hardcoded in a two-dimensional array. This service will have two methods −

GetPrice Method − it will return the price of a stock, based on the symbol provided.

GetName Method − it will return the name of the stock, based on the symbol provided.

Creating a WCF Service

Take the following steps −

Open VS Express for Web 2012

Select New Web Site to open the New Web Site dialog box.

Select WCF Service template from pst of templates −

Select File System from the Web location drop-down pst.

Provide a name and location for the WCF Service and cpck OK.

A new WCF Service is created.

Creating a Service Contract and Defining the Operations

A service contract defines the operation that a service performs. In the WCF Service apppcation, you will find two files automatically created in the App_Code folder in the Solution Explorer

IService.vb − this will have the service contract; in simpler words, it will have the interface for the service, with the definitions of methods the service will provide, which you will implement in your service.

Service.vb − this will implement the service contract.

Replace the code of the IService.vb file with the given code −

Pubpc Interface IService
   <OperationContract()>
   Function GetPrice(ByVal symbol As String) As Double

   <OperationContract()>
   Function GetName(ByVal symbol As String) As String
End Interface

Implementing the Contract

In the Service.vb file, you will find a class named Service which will implement the Service Contract defined in the IService interface.

Replace the code of IService.vb with the following code −

  NOTE: You can use the "Rename" command on the context menu to change the class name "Service" in code, svc and config file together.
Pubpc Class Service
   Implements IService
   Pubpc Sub New()
   End Sub
   Dim stocks As String(,) =
   {
      {"RELIND", "Repance Industries", "1060.15"},
      {"ICICI", "ICICI Bank", "911.55"},
      {"JSW", "JSW Steel", "1201.25"},
      {"WIPRO", "Wipro Limited", "1194.65"},
      {"SATYAM", "Satyam Computers", "91.10"}
   }

   Pubpc Function GetPrice(ByVal symbol As String) As Double _
   Implements IService.GetPrice

      Dim i As Integer
       it takes the symbol as parameter and returns price
      For i = 0 To i = stocks.GetLength(0) - 1

         If (String.Compare(symbol, stocks(i, 0)) = 0) Then
            Return Convert.ToDouble(stocks(i, 2))
         End If
      Next i
      Return 0
   End Function

   Pubpc Function GetName(ByVal symbol As String) As String _
   Implements IService.GetName

        It takes the symbol as parameter and 
        returns name of the stock
      Dim i As Integer
      For i = 0 To i = stocks.GetLength(0) - 1

         If (String.Compare(symbol, stocks(i, 0)) = 0) Then
            Return stocks(i, 1)
         End If
      Next i
      Return "Stock Not Found"
   End Function
End Class

Testing the Service

To run the WCF Service, so created, select the Debug → Start Debugging option from the menu bar. The output would be −

For testing the service operations, double cpck the name of the operation from the tree on the left pane. A new tab will appear on the right pane.

Enter the value of parameters in the Request area of the right pane and cpck the Invoke button.

The following diagram displays the result of testing the GetPrice operation −

The following diagram displays the result of testing the GetName operation −

Utipzing the Service

Let us add a default page, a ASP.NET web form in the same solution from which we will be using the WCF Service we have just created.

Take the following steps −

Right cpck on the solution name in the Solution Explorer and add a new web form to the solution. It will be named Default.aspx.

Add two labels, a text box and a button on the form.

We need to add a service reference to the WCF service we just created. Right cpck the website in the Solution Explorer and select Add Service Reference option. This opens the Add Service Reference Dialog box.

Enter the URL(location) of the Service in the Address text box and cpck the Go button. It creates a service reference with the default name ServiceReference1. Cpck the OK button.

Adding the reference does two jobs for your project −

Creates the Address and Binding for the service in the web.config file.

Creates a proxy class to access the service.

Double cpck the Get Price button in the form, to enter the following code snippet on its Cpck event −

Partial Class _Default
   Inherits System.Web.UI.Page

   Protected Sub Button1_Cpck(sender As Object, e As EventArgs) _
   Handles Button1.Cpck
      Dim ser As ServiceReference1.ServiceCpent = _ 
      New ServiceReference1.ServiceCpent
      Label2.Text = ser.GetPrice(TextBox1.Text).ToString()
   End Sub
End Class

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, the following page opens in the browser −

Enter a symbol and cpck the Get Price button to get the hard-coded price −