让两个对象间建立weak关系

让两个对象间建立weak关系

这是为了给两个对象间建立weak关系，当一个对象被释放时，另外一个对象再获取这个值时就是nil，也就是不持有这个对象:)

源码：

WeakRelatedDictionary.h 与 WeakRelatedDictionary.m

//

//  WeakRelatedDictionary.h

//  TestDemo

//

//  Created by YouXianMing on 14-9-25.

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import <Foundation/Foundation.h>

@interface WeakRelatedDictionary : NSObject

+ (void)addObject:(id)object forKey:(id)key;

+ (id)objectForKey:(id)key;

@end

//

//  WeakRelatedDictionary.m

//  TestDemo

//

//  Created by YouXianMing on 14-9-25.

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import "WeakRelatedDictionary.h"

static NSMapTable  *weakDictionary = nil;

@implementation WeakRelatedDictionary

+ (void)initialize

{

    if (self == [WeakRelatedDictionary class])

    {

        // 弱引用object弱引用object

        weakDictionary = [NSMapTable weakToWeakObjectsMapTable];

    }

}

+ (void)addObject:(id)object forKey:(id)key

{

    if (object == nil || key == nil)

    {

        NSLog(@"object or key should not be nil.");

        return;

    }

    if ([weakDictionary objectForKey:key] == nil)

    {

        [weakDictionary setObject:object forKey:key];

    }

}

+ (id)objectForKey:(id)key

{

    return [weakDictionary objectForKey:key];

}

@end

NSObject+WeakRelated.h 与 NSObject+WeakRelated.m

//

//  NSObject+WeakRelated.h

//  ScrollViewShowImage

//

//  Created by YouXianMing on 14-9-24.

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import <Foundation/Foundation.h>

@interface NSObject (WeakRelated)

// 与对象弱相关联系

- (void)setRelatedObject:(id)object;

// 取出建立关系的对象

- (id)relatedObject;

@end

//

//  NSObject+WeakRelated.m

//  ScrollViewShowImage

//

//  Created by YouXianMing on 14-9-24.

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import "NSObject+WeakRelated.h"

#import "WeakRelatedDictionary.h"

@implementation NSObject (WeakRelated)

- (void)setRelatedObject:(id)object

{

    [WeakRelatedDictionary addObject:object forKey:self];

}

- (id)relatedObject

{

    return [WeakRelatedDictionary objectForKey:self];

}

@end

测试代码：

Model.h 与 Model.m

//

//  Model.h

//  ObjectRelated

//

//  Created by YouXianMing on 14-9-27.

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import <Foundation/Foundation.h>

@interface Model : NSObject

@end

//

//  Model.m

//  ObjectRelated

//

//  Created by YouXianMing on 14-9-27.

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import "Model.h"

@implementation Model

@end

ViewController.m

//

//  ViewController.m

//  ObjectRelated

//

//  Created by YouXianMing on 14-9-27.

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import "ViewController.h"

#import "NSObject+WeakRelated.h"

#import "WeakRelatedDictionary.h"

#import "Model.h"

@interface ViewController ()

@property (nonatomic, strong) Model *model;

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    _model             = [Model new];

    self.relatedObject = _model;

    NSLog(@"%@", self.relatedObject);

    [self performSelector:@selector(showInfo) withObject:nil afterDelay:];

}

- (void)showInfo

{

    _model = nil;

    NSLog(@"%@", self.relatedObject);

}

@end