我做了一个被push到的controller,pop的时候,controller会释放,解析详见注释,欢迎批评指正!
#import "AnimaViewController.h"
@interface AnimaViewController ()
@property (nonatomic, strong) UIView *view1;
@property (nonatomic, strong) UIView *view2;
@property (nonatomic, copy) void (^block)(int);//self持有了block
@property (nonatomic, strong) UIButton *btn;
@property (nonatomic, strong) NSTimer *timer;
@end
@implementation AnimaViewController
__weak AnimaViewController *weakSelf;//用弱引用来跟踪self的释放情况。
- (void)viewDidLoad {
weakSelf = self;//指向self的弱引用。
[super viewDidLoad];
self.view1 = [[UIView alloc]initWithFrame:CGRectMake(0, 100, 90, 90)];
self.view1.backgroundColor = [UIColor orangeColor];
[self.view addSubview:self.view1];
self.view2 = [[UIView alloc]initWithFrame:CGRectMake(0, 300, 90, 90)];
self.view2.backgroundColor = [UIColor blueColor];
[self.view addSubview:self.view2];
self.btn = [[UIButton alloc]init];
self.btn.backgroundColor = [UIColor blackColor];;
[self.btn setFrame:CGRectMake(100, 100, 80, 80)];
[self.btn addTarget:self action:@selector(tapAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:self.btn];
//系统有时候会提示你可能导致循环引用,但会有漏掉的情况,比如strong变量定义成全局变量的时候。
__weak AnimaViewController *weakSelfLocal = self;//弱引用,引用计数不会增加。
self.block = ^ (int num){
__strong AnimaViewController *strongSelf = weakSelfLocal;//增加了对self的引用计数。
[strongSelf.btn setTitle:[NSString stringWithFormat:@"%d", num] forState:UIControlStateNormal];
[strongSelf.btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
//此后strongSelf变量作为局部strong变量,被系统发送了release消息(编译时就已插入release),所以strongSelf已经不构成对self的引用。如果将__weak AnimaViewController *weakSelfLocal定义为全局变量,那么此处strongSelf不会被release,所以仍然保持对self的强引用,则会导致循环引用。此处定义strong变量的用意是防止self被释放,导致此处的操作失效。
};
self.block(100);
NSLog(@"%@", weakSelf);//此处self没有被释放,所以对它的弱引用变量weakSelf不为null。
//关于注册通知中的block:The block is copied by the notification center and (the copy) held until the observer registration is removed.可见block中不能持有self的强引用,否则只有解除注册的时候,才能释放对self的持有,而self只有释放的时候才会在dealloc中解除通知的注册,则导致循环引用。所以要用弱引用代替self。
[[NSNotificationCenter defaultCenter]addObserverForName:@"blockretaincycle" object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) {
[weakSelfLocal.btn setTitle:[NSString stringWithFormat:@"%d", 888] forState:UIControlStateNormal];
[weakSelfLocal.btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
}];
//runloop对timer强引用,timer的target又强引用了self,self又强引用了timer,所以会循环引用,不会调用dealloc。
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:@selector(timerMethod)
userInfo:nil
repeats:YES];
}
- (void)timerMethod{
NSLog(@"%@", [NSDate date]);
}
- (void)tapAction:(UIButton *)sender{
//很多系统自带的block里,可以直接用self,不会循环引用。不清楚的可以看苹果官方文档。
[UIView animateWithDuration:1.0 animations:^{
[self.view1 setFrame:CGRectMake(100, 400, 70, 70)];
} completion:^(BOOL finished) {
[self.view1 setFrame:CGRectMake(100, 400, 70, 70)];
}];
}
- (void)dealloc{
NSLog(@"%@", weakSelf);//weakSelf是全局的,而此处打印为(null),说明self已经被释放。如果导致循环引用,则不会调用这个方法。
[[NSNotificationCenter defaultCenter]removeObserver:self name:@"blockretaincycle" object:nil];
// [self.timer invalidate];//写在这里没用,不会调用的
}
- (void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
[self.timer invalidate];//写在这里,确保退出页面的时候,timer失效,不会对self强引用,self可以销毁了。
}
@end