C和类集群模式

我已经阅读了关于类集群模式的一些信息，并且接下来会理解：

公共集群类只提供没有实际实现的接口，其他类实现不同的情况;

它与Abstract Factory模式有一些相似之处：当我们调用method +classNameWith...它依赖于参数可以选择最合适的子类并返回它。

例如， +[NSNumber numberWithDouble:1.0] ，将返回存储双+[NSNumber numberWithDouble:1.0]值的实现。

但我不明白：如何工作-init...公共集群类的方法： [[NSNumber alloc] initWithDouble:1.0] ，因为在调用alloc它已经分配了NSNumber实例，而不是它的子类。

那么，有人可以解释公共集群类的alloc-init方法实际上是如何工作的，以及何时具体的子类实例化并返回？

---

基本上，您分配的实例可能会被丢弃，并替换为其他实例。 从技术上讲，这不是特定于类集群的，这就是为什么当你在任何init方法中调用super ，你需要将结果设置为self ：

self = [super init];

---

这是Objective C的抽象工厂实现。

// Usage
    BrandingFactory * factory = [BrandingFactory factory:Sierra];

    UIView * view = [factory brandedView];

    UIButton * button = [factory brandedMainButton];

    UIToolbar * toolbar = [factory brandedToolbar];
____________________________________________
//  BrandingFactory.h
//  AbstractFactory

#import <Foundation/Foundation.h>

typedef enum ouputTypes {
    Acme,
    Sierra
} OutputTypes;

@interface BrandingFactory : NSObject 
{

}

+ (BrandingFactory *) factory: (OutputTypes)type;

- (UIView *) brandedView;
- (UIButton *) brandedMainButton;
- (UIToolbar *) brandedToolbar;

@end

___________________________________________________

//  BrandingFactory.m
//  AbstractFactory

#import "BrandingFactory.h"
#import "AcmeBrandingFactory.h"
#import "SierraBrandingFactory.h"


@implementation BrandingFactory

+ (BrandingFactory *) factory:(OutputTypes)type
{
    if (type == Sierra) {
        return [[[SierraBrandingFactory alloc] init] autorelease];
    }
    else if (type == Acme)
    {
        return [[[AcmeBrandingFactory alloc] init] autorelease];
    }
    return nil;

}

- (UIView *) brandedView
{
    return nil;
}

- (UIButton *) brandedMainButton
{
    return nil;
}

- (UIToolbar *) brandedToolbar
{
    return nil;
}

@end

________________________________________

//  SierraBrandingFactory.h
//  AbstractFactory

#import <Foundation/Foundation.h>
#import "BrandingFactory.h"


@interface SierraBrandingFactory : BrandingFactory
{

}

- (UIView*) brandedView;
- (UIButton*) brandedMainButton;
- (UIToolbar*) brandedToolbar;

@end


//  SierraBrandingFactory.m
//  AbstractFactory

#import "SierraBrandingFactory.h"
#import "SierraView.h"
#import "SierraMainButton.h"
#import "SierraToolbar.h"

@implementation SierraBrandingFactory

- (UIView*) brandedView
{
    // returns a custom view for Sierra
    return [[[SierraView alloc] init] autorelease];
}

- (UIButton*) brandedMainButton
{
    // returns a custom main button for Sierra
    return [[[SierraMainButton alloc] init] autorelease];
}

- (UIToolbar*) brandedToolbar
{
    // returns a custom toolbar for Sierra
    return [[[SierraToolbar alloc] init] autorelease];
}

@end

________________________________________
//  AcmeBrandingFactory.h
//  AbstractFactory


#import <Foundation/Foundation.h>
#import "BrandingFactory.h"


@interface AcmeBrandingFactory : BrandingFactory
{

}

- (UIView *) brandedView;
- (UIButton *) brandedMainButton;
- (UIToolbar *) brandedToolbar;

@end


//  AcmeBrandingFactory.m
//  AbstractFactory

#import "AcmeBrandingFactory.h"
#import "AcmeView.h"
#import "AcmeMainButton.h"
#import "AcmeToolbar.h"


@implementation AcmeBrandingFactory

- (UIView *) brandedView
{
    // returns a custom view for Acme
    return [[[AcmeView alloc] init] autorelease];
}

- (UIButton *) brandedMainButton
{
    // returns a custom main button for Acme
    return [[[AcmeMainButton alloc] init] autorelease];
}

- (UIToolbar *) brandedToolbar
{
    // returns a custom toolbar for Acme
    return [[[AcmeToolbar alloc] init] autorelease];
}

@end

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