// 有效释放 
- (void)viewWillDisappear:(BOOL)animated 
{ 
  [super viewWillDisappear:animated]; 
   
  [timer invalidate]; 
  timer = nil; 
} 
 
// 无效释放 
- (void)delloc 
{ 
  [timer invalidate]; 
  timer = nil; 
} 

timer.fireDate = [NSDate distantPast]; 

timer.fireDate = [NSDate distantFuture]; 

[timer setFireDate:[NSDate date]]; 

// 实例化方法1 初始化后即开始执行 
if (self.timer == nil) 
{ 
    self.time = 10.0; 
    // 带参数 
    NSNumber *number = @(self.time); 
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(countDownTime:) userInfo:number repeats:YES]; 
    // 非必要设置，实际已设置为 NSDefaultRunLoopMode 模式 
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes]; 
} 

// 关闭定时器方法1 
[self.timer invalidate]; 
self.timer = nil; 

// 实例化方法2 初始后化，需要调用" setFireDate "才开始执行 
if (self.timer == nil) 
{ 
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(countDownTime:) userInfo:nil repeats:YES]; 
    // 非必要设置，实际已设置为 NSDefaultRunLoopMode 模式 
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes]; 
    [self.timer setFireDate:[NSDate distantFuture]]; 
} 
self.time = 10.0; 
[self.timer setFireDate:[NSDate distantPast]]; 

// 关闭定时器方法2 
[self.timer setFireDate:[NSDate distantFuture]]; 

// 实例化方法3 初始化后，需要调用" fire "才开始执行 
if (self.timer == nil) 
{ 
    self.timer = [NSTimer timerWithTimeInterval:1.0 target: self selector:@selector(countDownTime:) userInfo:nil repeats:YES]; 
    // 必须设置 NSRunLoop 线程池，否则无效 
    [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes]; 
} 
self.time = 10.0; 
[self.timer fire]; 

// 关闭定时器方法3 
[self.timer invalidate]; 
self.timer = nil;