定时器 NSTimer 开始、暂停、继续、停止

if (_timer==nil) {
_timer = [NSTimer  scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(startFly) userInfo:nil repeats:YES];
}

if (_timer!=nil) {
//定时器暂
[_timer setFireDate:[NSDate distantFuture]]
}

if(_timer){
//定时器继续
[_timer  setFireDate:[NSDate distantPast]];
}

//停止定时器，销毁定时器
if (_timer) {
[_timer invalidate];
_timer = nil;
}