下面一段代码给大家介绍iOS MRC 下 block 循环引用问题
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//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);
}
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//
// 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
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//
// 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
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