定时器开启 关闭

创建一个定时器

    _timer = [NSTimer scheduledTimerWithTimeInterval:0.05
                                              target:self
                                            selector:@selector(setVoiceImage)
                                            userInfo:nil
                                             repeats:YES];
[[NSRunLoop currentRunLoop]addTimer:_timer forMode:NSDefaultRunLoopMode];
[_timer setFireDate:[NSDate distantFuture]];//关
[_timer setFireDate:[NSDate distantPast]];  //开启