iOS MRC 下 block 循环引用问题实例讲解

  //注意此__block会复制一份指针出来 一次原始的指针如果置为nil的话,此处复制出来的指针还是野指针 
    __block __typeof(self)weakSelf = self; 
    //__weak __typeof(self)weakSelf = self; 
    //__weak Person *weakSelf = self; 
    void (^block)(void) = ^(void){ 
      //NSLog(@"name --> is %@", self.name); 
      //NSLog(@"name --> is %@", weakSelf.name); 
      //这样判断会crash 此时weakSelf为野指针 
      //weakSelf 这时候是个野指针。。。野指针也是指针对吧？反正，这个野指针并不为NULL,虽然它指向的内存并未有什么鸟用， 
      //然而代码并不知道。所以 执行[weakSelf doSomething]; 必然闪退。 
      //注意此__block会复制一份指针出来 一次原始的指针如果置为nil的话,此处复制出来的指针还是野指针 
//      if (weakSelf) { 
//        NSLog(@"name --> is %@", weakSelf.name); 
//      } 
      //malloc(22); 
//      malloc_zon 
      //这并没有什么卵用。。。weakSelf 已经是野指针 照样crash 
//      __strong __typeof(weakSelf) strongSelf = weakSelf; 
//      if (weakSelf) { 
//        NSLog(@"name --> is %@", strongSelf.name); 
//      } 
      if (malloc_zone_from_ptr(weakSelf)) { 
        NSLog(@"name --> is %@", weakSelf.name); 
      } 

// 
// ViewController.m 
// test_mrc_block_self_01 
// 
// Created by jeffasd on 2017/12/1. 
// Copyright © 2017年 jeffasd. All rights reserved. 
// 
#import "ViewController.h" 
#import "Person.h" 
@interface ViewController () 
@property (nonatomic, copy) NSString *name; 
@end 
@implementation ViewController 
- (void)viewDidLoad { 
  [super viewDidLoad]; 
  self.view.backgroundColor = [UIColor whiteColor]; 
  self.name = @"xiaoming"; 
} 
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{ 
  self.view.backgroundColor = [UIColor cyanColor]; 
//  void (^block)(void) = ^(void){ 
//    NSLog(@"name --> is %@", self.name); 
//  }; 
//   
//   
//   
//  for (int i = 0; i < 30; i++) { 
//    block(); 
//  } 
  Person *xiaoming = [[Person alloc] init]; 
  //[xiaoming retain]; 
  [xiaoming release]; 
//  xiaoming = nil; 
  xiaoming = NULL; 
} 
- (void)didReceiveMemoryWarning { 
  [super didReceiveMemoryWarning]; 
  // Dispose of any resources that can be recreated. 
} 
@end 

// 
// Person.m 
// test_mrc_block_self_01 
// 
// Created by jeffasd on 2017/12/1. 
// Copyright © 2017年 jeffasd. All rights reserved. 
// 
#import "Person.h" 
#include <malloc/malloc.h> 
@interface Person () 
@property (nonatomic, copy) NSString *name; 
@end 
@implementation Person 
- (instancetype)init{ 
  if (self = [super init]) { 
    self.name = @"xiaoming"; 
    //注意此__block会复制一份指针出来 一次原始的指针如果置为nil的话,此处复制出来的指针还是野指针 
    __block __typeof(self)weakSelf = self; 
    //__weak __typeof(self)weakSelf = self; 
    //__weak Person *weakSelf = self; 
    void (^block)(void) = ^(void){ 
      //NSLog(@"name --> is %@", self.name); 
      //NSLog(@"name --> is %@", weakSelf.name); 
      //这样判断会crash 此时weakSelf为野指针 
      //weakSelf 这时候是个野指针。。。野指针也是指针对吧？反正，这个野指针并不为NULL,虽然它指向的内存并未有什么鸟用， 
      //然而代码并不知道。所以 执行[weakSelf doSomething]; 必然闪退。 
      //注意此__block会复制一份指针出来 一次原始的指针如果置为nil的话,此处复制出来的指针还是野指针 
//      if (weakSelf) { 
//        NSLog(@"name --> is %@", weakSelf.name); 
//      } 
      //malloc(22); 
//      malloc_zon 
      //这并没有什么卵用。。。weakSelf 已经是野指针 照样crash 
//      __strong __typeof(weakSelf) strongSelf = weakSelf; 
//      if (weakSelf) { 
//        NSLog(@"name --> is %@", strongSelf.name); 
//      } 
      if (malloc_zone_from_ptr(weakSelf)) { 
        NSLog(@"name --> is %@", weakSelf.name); 
      } 
    }; 
    for (int i = 0; i < 300; i++) { 
//      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
//        block(); 
//      }); 
      dispatch_async(dispatch_get_main_queue(), ^{ 
        block(); 
      }); 
    } 
  } 
  return self; 
} 
@end