iOS MRC 下 block 循环引用问题实例讲解

下面一段代码给大家介绍ios mrc 下 block 循环引用问题            

  //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 

总结

以上所述是小编给大家介绍的ios mrc 下 block 循环引用问题，希望对大家有所帮助