Basic Objective-C
Advanced Objective-C
Objective-C Useful Resources
Selected Reading
- Command-Line Arguments
- Objective-C - Error Handling
- Objective-C - Log Handling
- Objective-C - Type Casting
- Objective-C - Typedef
- Objective-C - Preprocessors
- Objective-C - Structures
- Objective-C - Strings
- Objective-C - Pointers
- Objective-C - Arrays
- Objective-C - Numbers
- Objective-C - Blocks
- Objective-C - Functions
- Objective-C - Decision Making
- Objective-C - Loops
- Objective-C - Operators
- Objective-C - Constants
- Objective-C - Variables
- Objective-C - Data Types
- Objective-C - Basic Syntax
- Objective-C - Program Structure
- Objective-C - Environment Setup
- Objective-C - Overview
- Objective-C - Home
Advanced Objective-C
- Obj-C - Memory Management
- Objective-C - Fast Enumeration
- Obj-C - Foundation Framework
- Objective-C - Composite Objects
- Objective-C - Dynamic Binding
- Objective-C - Protocols
- Objective-C - Extensions
- Objective-C - Posing
- Objective-C - Categories
- Objective-C - Data Encapsulation
- Objective-C - Polymorphism
- Objective-C - Inheritance
- Objective-C - Classes & Objects
Objective-C Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
Objective-C - Composite Objects
Objective-C Composite Objects
We can create subclass within a class cluster that defines a class that embeds within it an object. These class objects are composite objects. So you might be wondering what s a class cluster. So we will first see what s a class cluster.
Class Clusters
Class clusters are a design pattern that the foundation framework makes extensive use of. Class clusters group a number of private concrete subclasses under a pubpc abstract superclass. The grouping of classes in this way simppfies the pubpcly visible architecture of an object-oriented framework without reducing its functional richness. Class clusters are based on the abstract factory design pattern.
To make it simple, instead of creating multiple classes for similar functions, we create a single class that will take care of its handpng based on the value of input.
For example, in NSNumber we have many clusters of classes pke char, int, bool and so on. We group all of them to a single class that takes care of handpng the similar operations in a single class. NSNumber actually wraps the value of these primitive types into objects.
What is a Composite Object?
By embedding a private cluster object in an object of our own design, we create a composite object. This composite object can rely on the cluster object for its basic functionapty, only intercepting messages that the composite object wants to handle in some particular way. This architecture reduces the amount of code we must write and lets you take advantage of the tested code provided by the Foundation Framework.
This is explained in the following figure.
The composite object must declare itself to be a subclass of the cluster s abstract superclass. As a subclass, it must override the superclass primitive methods. It can also override derived methods, but this isn t necessary because the derived methods work through the primitive ones.
The count method of the NSArray class is an example; the intervening object s implementation of a method it overrides can be as simple as −
- (unsigned)count {
return [embeddedObject count];
}
In the above example, embedded object is actually of type NSArray.
A Composite Object Example
Now in order to see a complete example, let s look at the example from the Apple documentation which is given below.
#import <Foundation/Foundation.h>
@interface VapdatingArray : NSMutableArray {
NSMutableArray *embeddedArray;
}
+ vapdatingArray;
- init;
- (unsigned)count;
- objectAtIndex:(unsigned)index;
- (void)addObject:object;
- (void)replaceObjectAtIndex:(unsigned)index withObject:object;
- (void)removeLastObject;
- (void)insertObject:object atIndex:(unsigned)index;
- (void)removeObjectAtIndex:(unsigned)index;
@end
@implementation VapdatingArray
- init {
self = [super init];
if (self) {
embeddedArray = [[NSMutableArray allocWithZone:[self zone]] init];
}
return self;
}
+ vapdatingArray {
return [[self alloc] init] ;
}
- (unsigned)count {
return [embeddedArray count];
}
- objectAtIndex:(unsigned)index {
return [embeddedArray objectAtIndex:index];
}
- (void)addObject:(id)object {
if (object != nil) {
[embeddedArray addObject:object];
}
}
- (void)replaceObjectAtIndex:(unsigned)index withObject:(id)object; {
if (index <[embeddedArray count] && object != nil) {
[embeddedArray replaceObjectAtIndex:index withObject:object];
}
}
- (void)removeLastObject; {
if ([embeddedArray count] > 0) {
[embeddedArray removeLastObject];
}
}
- (void)insertObject:(id)object atIndex:(unsigned)index; {
if (object != nil) {
[embeddedArray insertObject:object atIndex:index];
}
}
- (void)removeObjectAtIndex:(unsigned)index; {
if (index <[embeddedArray count]) {
[embeddedArray removeObjectAtIndex:index];
}
}
@end
int main() {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
VapdatingArray *vapdatingArray = [VapdatingArray vapdatingArray];
[vapdatingArray addObject:@"Object1"];
[vapdatingArray addObject:@"Object2"];
[vapdatingArray addObject:[NSNull null]];
[vapdatingArray removeObjectAtIndex:2];
NSString *aString = [vapdatingArray objectAtIndex:1];
NSLog(@"The value at Index 1 is %@",aString);
[pool drain];
return 0;
}
Now when we compile and run the program, we will get the following result.
2013-09-28 22:03:54.294 demo[6247] The value at Index 1 is Object2
In the above example, we can see that vapdating array s one function would not allow adding null objects that will lead to crash in the normal scenario. But our vapdating array takes care of it. Similarly, each of the method in vapdating array adds vapdating processes apart from the normal sequence of operations.
Advertisements