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，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对网站的支持！