如何确定平移手势的真实结束速度？

Question

当使用UIPanGestureRecognizer和检测时UIGestureRecognizerStateEnded,手势的速度不是真正的速度.相反,它是我之前调用我的动作方法的旧速度.如何在手势结束时访问真实速度？

我创建了UIPanGestureRecognizer这样的:

    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];

我的动作方法的开头是:

- (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)

正如你所看到的,两个日志条目中的速度是相同的(相同的翻译故事,但我只关心速度),虽然我在不移动它的情况下按住我的手指约30秒,然后抬起手指.您可以从条目的时间戳中分辨出时间.在不移动我的手指30秒后肯定不会报告速度.

我用iOS 6.1的iOS模拟器测试了这个.

Answer 1

velocityInView仅在发生平移时才定义该方法.也就是说,只有当您实际移动手指时才会发生平移手势.如果你保持手指不动,它实际上不会触发平移手势.

这意味着没有内置方法来了解手势结束时的移动速度.您可以执行以下操作:检查上一个事件与状态值之间的时差为UIGestureRecognizerStateChanged和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;
    }   
 }