ios - 使用平移手势重置 UIView 的框架，无需硬编码起始值

Question

我有一个附加到 UIView 的 UIPanGestureRecognizer。我想做的基本上是拖放到一个桶中。如果用户放开 UIView 而它不在桶中，我希望它以动画方式回到其原始开始位置。为我的 UIPanGestureRecognizer 调用的选择器是:

- (void)handleDragDescriptionView:(UIPanGestureRecognizer *)gestureRecognizer {
    UIView *panViewPiece = [gestureRecognizer view];
    CGRect originalFrame = CGRectMake(946, 20, 58, 30);

    CGPoint translation = [gestureRecognizer translationInView:panViewPiece];
    if (gestureRecognizer.state == UIGestureRecognizerStateBegan || gestureRecognizer.state == UIGestureRecognizerStateChanged) {
        panViewPiece.center = CGPointMake(panViewPiece.center.x + translation.x, panViewPiece.center.y + translation.y);

        [gestureRecognizer setTranslation:CGPointZero inView:panViewPiece.superview];
    }
    else if (gestureRecognizer.state == UIGestureRecognizerStateCancelled) {
        [UIView animateWithDuration:0.25 animations:^{
            self.dragDescriptionView.frame = originalFrame;
        }];
    }
    else {
        [UIView animateWithDuration:0.25 animations:^{
            self.dragDescriptionView.frame = originalFrame;
        }];
    }

}

我想知道我是否可以在方法顶部没有 originalFrame 的情况下执行此操作。我原来有

CGRect originalFrame = _dragDescriptionView.frame; 

而不是硬编码，但它不会回弹。可能是因为我在拖动时正在更新该值。我不是特别喜欢硬编码值，但我不确定是否有办法解决这个问题。谢谢!

Answer 1

您实际上只需要跟踪 View 的原始中心。将 originalCenter 设为实例变量，并仅在手势开始时设置它:

@implementation MyViewController {
    CGPoint _originalCenter;
}

- (void)handleDragDescriptionView:(UIPanGestureRecognizer *)gestureRecognizer {
    UIView *panViewPiece = [gestureRecognizer view];

    switch (gestureRecognizer.state) {
        case UIGestureRecognizerStateBegan:
            _originalCenter = panViewPiece.center;
            break;

        case UIGestureRecognizerStateChanged: {
            CGPoint translation = [gestureRecognizer translationInView:panViewPiece.superview];
            panViewPiece.center = CGPointMake(panViewPiece.center.x + translation.x, panViewPiece.center.y + translation.y);
            [gestureRecognizer setTranslation:CGPointZero inView:panViewPiece.superview];
            break;
        }

        case UIGestureRecognizerStateEnded:
        case UIGestureRecognizerStateCancelled: {
            [UIView animateWithDuration:0.25 animations:^{
                panViewPiece.center = _originalCenter;
            }];
            break;
        }

        default:
            break;
    }
}