iOS 音序器速度 slider 导致应用程序崩溃

Question

我使用 Objective C 创建了一个鼓音序器。我想要 slider 来控制速度。目前，一切正常，每一步之间的间隔由以下因素控制:

 while (self.running)
        {
            // sleep until the next step is due
            [NSThread sleepUntilDate:time];

            // update step
            int step = self.step + 1;

            // wrap around if we reached NUMSTEPS
            if (step >= NUMSTEPS)
                step = 0;

            // store
            self.step = step;

            // time duration until next step
            time = [time dateByAddingTimeInterval:0.2];
        }

所以每一步之间的时间是0.2秒。我已经尝试在 View Controller .m 中实现这样的速度 slider ( slider 的范围为 0.3 到 1.0，因此将输出与当前时间相似的值):

- (IBAction)sliderMoved:(UISlider *)sender
    {

        AppDelegate* app = [[UIApplication sharedApplication] delegate];
        app.tempo = sender.value;
    }

并将 while(self.running) 线程中的行更改为:

time = [time dateByAddingTimeInterval: (NSTimeInterval) _tempo];

但是，这会导致步骤之间的时间太短(节奏快得离谱)，并且当触摸应用中的任何控件时，它会崩溃。

我想知道我是否需要设置这样的功能，但我不确定里面有什么可以使速度 slider 工作:

- (void)setTempo:(float)tempo
{

}

我已经尽力说清楚了，如果有人能帮助我，我将不胜感激，在此先感谢

Answer 1

-(void) startDrumTick{
    [self.myDrumTimer invalidate]; // stop any current existing timer

    // perform the call to the method 'drumMethodOperation:'
    // every 0.2 sec. NB: drumMethodOperation will run on main thread.
    // this means that if you expect to do long-blocking operation, 
    // you will need to move that op to an async thread, in order to avoid
    // the UI blocking

    self.myDrumTimer = [NSTimer scheduledTimerWithTimeInterval:0.2
                          target:self
                          selector:@selector(drumMethodOperation:)
                          userInfo:nil
                          repeats:YES];        
}

-(void)drumMethodOperation:(id)sender
{
    // update step
    int step = self.step + 1;

    // wrap around if we reached NUMSTEPS
    if (step >= NUMSTEPS)
        step = 0;

    // store
    self.step = step;

    // any other needed operation to run every 0.2 secs
}

下面是一个使用 GCD 进行异步线程管理的例子

dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){

    // Long blocking operation ( DO NOT PERFORM ANY UI OPERATION, like changing a text label, setting an image to an UIImageView, etc. )

    [self myLongDbQuery];

    dispatch_async(dispatch_get_main_queue(), ^(void){
        //Perform you UI Updates here
        self.myLabel.text = @"Query done!!!";
    });
});

希望对你有帮助