NSTimer计时器后台运行的解决方法

思路：

切换至后台计时器暂停，记录下当前时间，切换回前台计时器回复，计算中间时间差

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationEnterBackground) name:UIApplicationDidEnterBackgroundNotification object:nil];    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationEnterForeground) name:UIApplicationDidBecomeActiveNotification object:nil];

-(void)applicationEnterBackground{    _lastTime = CACurrentMediaTime();    if(self.runningTimer){        [self.timer setFireDate:[NSDate distantFuture]];    }}-(void)applicationEnterForeground{    double time = CACurrentMediaTime();    self.totalTime += (int)((time - _lastTime) * 100);    if(self.runningTimer){        [self.timer setFireDate:[NSDate date]];    }}

我这里用的是毫秒所以*100了