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
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@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)
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@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:
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@protocol HSDogDelegate <NSObject> @end @interface HSDog : NSObject @property (nonatomic, weak) id<HSDogDelegate>delegate; @end |
HSPerson.m:
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#import "HSDog.h" @implementation HSDog - (void)dealloc { NSLog(@"HSDog----销毁"); } @end |
HSPerson类
HSPerson.h:
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@interface HSPerson : NSObject @end |
HSPerson.m:
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#import "HSPerson.h" #import "HSDog.h" @interface HSPerson() /** 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：
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#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
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@property (nonatomic, weak) id<HSDogDelegate>delegate; |
运行->打印：
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HSPerson----销毁 HSDog----销毁 |
strong修饰代理
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@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
person对dog强引用
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@property (nonatomic, strong) HSDog *dog; person |
self.dog.delegate又对person强引用，使person的retainCount + 1
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@property (nonatomic, strong) id<HSDogDelegate>delegate; |
当viewController不对person引用后，dog.delegate对person还强引用着，person的retainCount为1，所以person不会释放，dog固然也不会释放，这就是造成循环引用的导致内存泄露的原因！
- 使用weak
person对dog强引用
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@property (nonatomic, strong) HSDog *dog; person |
self.dog.delegate只对person弱引用，并未使person的retainCount + 1
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@property (nonatomic, weak) id<HSDogDelegate>delegate; |
所以当viewController不对person引用后，person的retainCount为0，即person会被释放，那么dog也被释放
