如何确定平移手势的真实结束速度？

使用时UIPanGestureRecognizer并检测UIGestureRecognizerStateEnded，那么手势的速度就不是真实的速度。相反，它是先前调用我的操作方法的旧速度。如何获取手势结束时的真实速度？

我创建我的UIPanGestureRecognizer像这样：

    UIPanGestureRecognizer* panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panGestureRecognized:)];
    [panGestureRecognizer setMaximumNumberOfTouches:2];
    [panGestureRecognizer setMinimumNumberOfTouches:1];
    [panGestureRecognizer setDelegate:self];
    [panGestureRecognizer setDelaysTouchesBegan:NO];
    [panGestureRecognizer setDelaysTouchesEnded:NO];
    [panGestureRecognizer setCancelsTouchesInView:NO];
    [self addGestureRecognizer:panGestureRecognizer];

我的操作方法的开头在这里：

- (IBAction) panGestureRecognized:(UIPanGestureRecognizer *)recognizer {

    UIGestureRecognizerState state = recognizer.state;

    CGPoint gestureTranslation = [recognizer translationInView:self];
    CGPoint gestureVelocity = [recognizer velocityInView:self];

    [CBAppDelegate log:@"panGestureRecognized: state: %s\n    translation: (%f, %f)\n    velocity: (%f, %f)", [self toString:state], gestureTranslation.x, gestureTranslation.y, gestureVelocity.x, gestureVelocity.y];

日志输出示例：

2013-09-30_10:46:32.830 panGestureRecognized: state: UIGestureRecognizerStateChanged
    translation: (-283.000000, 2.000000)
    velocity: (-43.046783, 45.551472)
2013-09-30_10:47:02.942 panGestureRecognized: state: UIGestureRecognizerStateEnded
    translation: (-283.000000, 2.000000)
    velocity: (-43.046783, 45.551472)

正如您所看到的，两个日志条目中的速度是相同的（翻译相同，但我只关心速度），尽管我按住手指大约 30 秒没有移动，然后抬起手指。您可以从条目的时间戳判断时间。手指不动 30 秒后，当然不应该报告速度。

我已经使用 iOS 6.1 的 iPhone 的 iOS 模拟器对此进行了测试。

The velocityInView仅当平移发生时才定义方法。也就是说，仅当您实际移动手指时才会发生平移手势。如果您保持手指不动，它实际上不会触发平移手势。

这意味着没有内置方法可以知道手势结束时的移动速度。您可以执行类似检查最后一个事件与状态值之间的时间差之类的操作UIGestureRecognizerStateChanged and UIGestureRecognizerStateEnded。然后，您可以调整此阈值以获得所需的行为。

例如

- (IBAction) panGestureRecognized:(UIPanGestureRecognizer *)recognizer {

    UIGestureRecognizerState state = recognizer.state;

    CGPoint gestureTranslation = [recognizer translationInView:self];
    CGPoint gestureVelocity = [recognizer velocityInView:self];

    if ( state == UIGestureRecognizerStateChanged )
         _lastChange = CFAbsoluteTimeGetCurrent();
    else if ( state == UIGestureRecognizerStateEnded ) {
         double curTime = CFAbsoluteTimeGetCurrent(); 
         double timeElapsed = curTime - _lastChange;
         if ( timeElapsed < MY_THRESHOLD )
              finalSpeed = gestureVelocity;
         else
              finalSpeed = CGPointZero;
    }   
 }