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