iOS 代理为啥要用weak修饰? (刨根问底一)

旧城等待， 2022-08-20 14:11 269阅读 0赞

转载地址： http://www.jianshu.com/p/398472616435

# iOS 代理为啥要用weak修饰? (刨根问底一) #

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`在开发中我们经常使用代理，或自己写个代理，而代理属性都用weak(assign)修饰，看过有些开发者用strong(retain)，但并没发现有何不妥，也不清楚weak(assign)与strong(retain)修饰有何区别`

`功能实现就行了，考虑这么多干嘛~~~我只能哈哈哈`

*  `weak`:`指明该对象并不负责保持delegate这个对象，delegate这个对象的销毁由外部控制`

@property (nonatomic, weak) id<HSDogDelegate>delegate;

*  `strong`：`该对象强引用delegate，外界不能销毁delegate对象，会导致循环引用(Retain Cycles)`

@property (nonatomic, strong) id<HSDogDelegate>delegate;

`可能你还不太理解，没关系，下面先举例，看结果，再分析！`

### 举例 ###

*  `HSDog类`

`HSDog.h`:

@protocol HSDogDelegate <NSObject>
    @end
    
    @interface HSDog : NSObject
    
    @property (nonatomic, weak) id<HSDogDelegate>delegate;
    
    @end

`HSPerson.m`:

#import "HSDog.h"
    
    @implementation HSDog
    
    - (void)dealloc
    {
        NSLog(@"HSDog----销毁");
    }
    
    @end

*  `HSPerson类`

`HSPerson.h`:

@interface HSPerson : NSObject
    
    @end

`HSPerson.m`:

#import "HSPerson.h"
    #import "HSDog.h"
    
    @interface HSPerson()<HSDogDelegate>
    /** 强引用dog*/
    @property (nonatomic, strong) HSDog *dog;
    @end
    
    @implementation HSPerson
    
    - (instancetype)init
    {
        self = [super init];
        if (self) {
            // 实例化dog
            self.dog = [[HSDog alloc] init];
            // dog的delegate引用self,self的retainCount，取决于delegate修饰，weak：retainCount不变，strong：retainCount + 1
            self.dog.delegate = self;
    
        }
        return self;
    }
    
    - (void)dealloc
    {
        NSLog(@"HSPerson----销毁");
    }
    
    @end

*  `在ViewController实现`：

#import "ViewController.h"
    #import "HSPerson.h"
    
    @interface ViewController ()
    @end
    
    @implementation ViewController
    - (void)viewDidLoad {
        [super viewDidLoad];
        // 实例化person, self对person弱引用，person的retainCount不变
        HSPerson *person = [[HSPerson alloc] init];
    
    }
    @end

### `结果`： ###

*  `weak修饰代理`

@property (nonatomic, weak) id<HSDogDelegate>delegate;

`运行->打印`：

HSPerson----销毁 HSDog----销毁

*  `strong修饰代理`

@property (nonatomic, strong) id<HSDogDelegate>delegate;

`运行->打印`：  
`....并未打印，说明HSPerson、HSDog对象没调用dealloc方法，两个对象未销毁`  
`这也是我们经常说的内存泄露，该释放的内存并未释放！`

### `分析`： ###

*  `使用strong`

![20150814154541526][]

`person对dog强引用`