将velocityInView与UIPanGestureRecognizer结合使用

Question

我有一个自定义滑块类型的对象，我希望使其更有用。目前我使用 UIPanGestureRecognizer 和 translationInView 来使其工作。它工作得很好，但我想要某种速度，让它感觉更有用。我已经尝试了一些方法，但无法完全弄清楚如何正确实现速度 changedLevel 方程。

- (void)panDetected:(UIPanGestureRecognizer *)gesture {

    CGPoint swipeLocation = [gesture locationInView:self.tableView];
    NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:swipeLocation];
    LevelCounterTableCell *swipedCell = (LevelCounterTableCell *)[self.tableView cellForRowAtIndexPath:indexPath];

    if([gesture state] == UIGestureRecognizerStateBegan) {
        NSString *originalLevelString = swipedCell.levelNumber.text;
        originalLevel = [originalLevelString intValue]; // int originalLevel
    }

    if ([gesture state] == UIGestureRecognizerStateChanged) {

        CGFloat xTranslation = [gesture translationInView:[[gesture view] superview]].x;
        CGFloat xVelocity = [gesture velocityInView: [[gesture view] superview]].x;

        // Pan threshold is currently set to 8.0. 
        // 8.0 is a decent level for slow panning
        // for fast panning 2.0 is more reasonable
        changedLevel = ceilf((xTranslation / panThreshold) + originalLevel); // int changedLevel

        // Raw velocity seems to go from around 3 (slow)
        // to over 200 (fast)
        NSLog(@"raw velocity = %f", xVelocity);

        if (changedLevel >= 15 && changedLevel <= 100) {
            swipedCell.levelNumber.text = [NSString stringWithFormat:@"%i", changedLevel];
            swipedCell.meter.frame = [self updateMeter: changedLevel];

        }
    }

    if ([gesture state] == UIGestureRecognizerStateEnded || [gesture state] == UIGestureRecognizerStateCancelled) {
        if (changedLevel >= 15 && changedLevel <= 100) {
            //... Save the values...            
        }

    }
}

任何帮助将不胜感激。谢谢。

Answer 1

根据我的经验，在用户抬起手指并且识别器完成之前，平移手势识别器的 velocityInView: 并不重要。此时，您可以使用速度来计算移动视图的动画持续时间。

只需坚持使用 translationInView: 直到 state 为 UIGestureRecognizerStateEnded，然后使用 velocityInView: 为任何屏幕视图更改添加动画效果。