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