避免滑动tableView时对NSTimer的干扰

NSTimer *timer = [[NSTimer alloc]init];

    timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timeLabelDisplay) userInfo:nil repeats:YES];

    NSRunLoop *main = [NSRunLoop currentRunLoop];

    [main addTimer:timer forMode:NSRunLoopCommonModes];