demo放在了GitHub

内存泄漏的原因：

self强引用timer。timer添加在runloop上，只要timer不销毁self就销毁不了。当然了你可以选择在viewWillDisappear中销毁timer。但是定时器页面不一定都是pop到上一个页面，也有可能push新页面，也有可能是进入后台，这样我们希望重新回到定时器页面的时候，定时任务还依旧是执行状态。所以invalidate放到viewWillDisappear是不合理的，唯一合理的地方就是定时器页面销毁的时候销毁timer。这就引出了以下三种解决方法。

第一、二种方法是在合适的时机销毁timer，干掉强引用。

第三种方法是自定义timer，弱引用timer，从源头上就不形成循环引用，更不会导致内存泄漏。

一、离开当前控制器销毁NSTimer

didMoveToParentViewController方法了解一下

@interface WLZSecondController ()

@property (nonatomic, strong)UILabel *label;

@property (nonatomic, assign)int repeatTime;

//第一、二种的属性

//@property (nonatomic, strong)NSTimer *timer;

//第三种方法的属性

@property (nonatomic, strong)WLZTimer *timer;

@end

@implementation WLZSecondController

- (void)didReceiveMemoryWarning {

[super didReceiveMemoryWarning];

// Dispose of any resources that can be recreated.

}

- (void)viewDidLoad {

[super viewDidLoad];

self.view.backgroundColor = [UIColor yellowColor];

self.repeatTime = 60;

self.label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 200, 50)];

self.label.text = @"60";

self.label.textColor = [UIColor blackColor];

[self.view addSubview:self.label];

[self createTimer];

}

#pragma mark - 第一种方法

- (void)createTimer{

self.timer = [NSTimer timerWithTimeInterval:1 target:self selector:@selector(change) userInfo:nil repeats:YES];

[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];

}

- (void)didMoveToParentViewController:(UIViewController *)parent{

if(parent == nil){

[self.timer invalidate];

}

}

- (void)change{

self.repeatTime --;

self.label.text = [NSString stringWithFormat:@"%d",self.repeatTime];

if(self.repeatTime == 0){

[self.timer invalidate];

}

}

- (void)dealloc{

NSLog(@"dealloc");

}

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二、自定义返回按钮销毁NSTimer

这种方法就需要禁止掉侧滑返回手势。

#pragma mark - 第二种方法 这里只是随意创建了一个button，具体的图片、文案可以自己调试。

- (void)createTimer{

self.timer = [NSTimer timerWithTimeInterval:1 target:self selector:@selector(change) userInfo:nil repeats:YES];

[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];

}

- (void)viewWillAppear:(BOOL)animated{

[self changeBackBarButtonItem];

}

- (void)changeBackBarButtonItem{

self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(invalidateTimer)];

}

- (void)invalidateTimer{

[self.timer invalidate];

[self.navigationController popViewControllerAnimated:YES];

}

- (void)change{

self.repeatTime --;

self.label.text = [NSString stringWithFormat:@"%d",self.repeatTime];

if(self.repeatTime == 0){

[self.timer invalidate];

}

}

- (void)dealloc{

NSLog(@"dealloc");

}

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三、自定义timer，压根不形成循环引用

自定义timer类

.h文件

@interface WLZTimer : NSObject

@property (nonatomic, weak)id target;

@property (nonatomic, assign)SEL selector;

///创建timer

- (instancetype)initWithTimeInterval:(NSTimeInterval)interval Target:(id)target andSelector:(SEL)selector;

///销毁timer

- (void)closeTimer;

@end

.m文件

@interface WLZTimer ()

@property (nonatomic, strong)NSTimer *timer;

@end

@implementation WLZTimer

- (instancetype)initWithTimeInterval:(NSTimeInterval)interval Target:(id)target andSelector:(SEL)selector{

if(self == [super init]){

self.target = target;

self.selector = selector;

self.timer = [NSTimer scheduledTimerWithTimeInterval:interval target:self selector:@selector(dosomething) userInfo:nil repeats:YES];

}

return self;

}

- (void)dosomething{

//这里是为了不阻塞主线程

dispatch_async(dispatch_get_main_queue(), ^{

id target = self.target;

SEL selector = self.selector;

if([target respondsToSelector:selector]){

[target performSelector:selector withObject:nil];

}

});

}

- (void)closeTimer{

[self.timer invalidate];

self.timer = nil;

}

- (void)dealloc{

NSLog(@"WLZTimer dealloc");

}

@end

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自定义timer在主线程异步执行任务不明白原因的话，可参考文章iOS线程、同步异步、串行并行队列

创建timer的时候就用自定义的类就可以

#pragma mark - 第三种方法

/*

* 与第前两种不同的是：前两种只是在合适的时机解决循环引用，

* 第三种根本就不会造成循环引用，可以封装起来供多个地方使用，而且遵循单一职责原则

*

*/

- (void)createTimer{

self.timer = [[WLZTimer alloc] initWithTimeInterval:1 Target:self andSelector:@selector(change)];

}

- (void)change{

self.repeatTime --;

self.label.text = [NSString stringWithFormat:@"%d",self.repeatTime];

if(self.repeatTime == 0){

[self.timer closeTimer];

}

}

- (void)dealloc{

[self.timer closeTimer];

NSLog(@"dealloc");

}

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2019/1/17 更新

四、定义中介继承NSObject进行消息转发消除强引用NSTimer

+ (instancetype)proxyWithTarget:(id)aTarget{

TFQProxy *proxy = [[TFQProxy alloc] init];

proxy.target = aTarget;

return proxy;

}

//自己不能处理这个消息，就会调用这个方法来消息转发，return target，让target来调用这个方法。

- (id)forwardingTargetForSelector:(SEL)aSelector{

if([self.target respondsToSelector:aSelector]){

return self.target;

}

return nil;

}

复制代码self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:[TFQProxy proxyWithTarget:self] selector:@selector(repeatAction:) userInfo:nil repeats:YES];

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五、定义中介继承NSProxy进行消息转发消除强引用NSTimer

+ (instancetype)proxyWithTarget:(id)aTarget{

TFQProxySubclass *proxy = [TFQProxySubclass alloc];

proxy.target = aTarget;

return proxy;

}

//为另一个类实现的消息创建一个有效的方法签名

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel{

return [self.target methodSignatureForSelector:sel];

}

//将选择器转发给一个真正实现了该消息的对象

- (void)forwardInvocation:(NSInvocation *)invocation{

[invocation invokeWithTarget:self.target];

}

复制代码self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:[TFQProxySubclass proxyWithTarget:self] selector:@selector(repeatAction:) userInfo:nil repeats:YES];

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tips：五比四效率高，因为5是系统的类，直接进行消息转发，4会走几条弯路才会到消息转发那个方法

六、GCD创建定时器

/**

GCD创建定时器

@param task 定时器内容

@param interval 执行间隔

@param repeat 是否重复

@param async 是否异步

@param identifier 定时器唯一ID

@return 返回定时器唯一ID，销毁的时候用

*/

+ (NSString *)schedleTask:(void (^)(void))task interval:(NSTimeInterval)interval repeat:(BOOL)repeat async:(BOOL)async reuseIdentifier:(NSString *)identifier{

dispatch_queue_t queue = async ? dispatch_get_global_queue(0, 0) : dispatch_get_main_queue();

//穿件定时器

dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);

//开始时间

dispatch_time_t start = dispatch_time(DISPATCH_TIME_NOW, 0*NSEC_PER_SEC);

//设置各种时间

dispatch_source_set_timer(timer, start, interval*NSEC_PER_SEC, 0);

//设置回调

dispatch_source_set_event_handler(timer, ^{

task();

if(!repeat){

[self cancelTimer:identifier];

}

});

//启动定时器

dispatch_resume(timer);

timerDict[identifier] = timer;

return identifier;

}

+ (void)cancelTimer:(NSString *)identifier{

dispatch_source_cancel(timerDict[identifier]);

[timerDict removeObjectForKey:identifier];

}

复制代码__weak typeof(self) weakSelf = self;

self.timerIdentifier = [TFQGCDTimer schedleTask:^{

[weakSelf repeatAction:nil];

} interval:1 repeat:YES async:NO reuseIdentifier:@"identifier"];

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