举例

• HSDog类
  
  HSDog.h:
  
  @protocol HSDogDelegate <NSObject>
  
  @end
  
  @interface HSDog : NSObject
  
  @property (nonatomic, weak) id<HSDogDelegate>delegate;
  
  @end
  
  HSDog.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！