UIPinchGestureRecognizer 将捏合视图定位在两根手指之间

Question

我成功地实现了视图的捏合缩放。然而，视图并没有位于我希望的位置。对于 iPad 上的 stackoverflowers，我希望我的视图能够像 iPad Photos.app 一样居中：当您捏合并缩放相册时，照片会以不断扩展的视图呈现。该视图大致以第一根手指的右上角和另一根手指的左下角为中心。我将它与平移识别器混合在一起，但这样用户总是需要捏合，然后平移进行调整。

这里有非常图形化的解释，如果不清楚的话我可以发布我的应用程序的视频（这不是秘密，我正在尝试重现 iPad 的 Photos.app...）

因此，对于手指的初始位置，开始缩放：

这是目前实际的“缩放”框架。正方形更大，但位置在手指下方

这是我想要的：相同大小，但 origin.x 和 y 不同：

（抱歉我的 Photoshop 技巧很差 ^^）

Answer 1

您可以通过handlingPinchGesture方法中的以下代码获取两根手指之间的中点的CGPoint。

CGPoint point = [sender locationInView:self];

我的整个 handlePinchGesture 方法如下。

/*
instance variables

CGFloat lastScale;
CGPoint lastPoint;
*/

- (void)handlePinchGesture:(UIPinchGestureRecognizer *)sender {
    if ([sender numberOfTouches] < 2)
        return;

    if (sender.state == UIGestureRecognizerStateBegan) {
        lastScale = 1.0;
        lastPoint = [sender locationInView:self];
    }

    // Scale
    CGFloat scale = 1.0 - (lastScale - sender.scale);
    [self.layer setAffineTransform:
        CGAffineTransformScale([self.layer affineTransform], 
                               scale, 
                               scale)];
    lastScale = sender.scale;

    // Translate
    CGPoint point = [sender locationInView:self];
    [self.layer setAffineTransform:
        CGAffineTransformTranslate([self.layer affineTransform], 
                                   point.x - lastPoint.x, 
                                   point.y - lastPoint.y)];
    lastPoint = [sender locationInView:self];
}

Answer 2

查看 Touches 示例项目。具体来说，这些方法可以帮助您：

// scale and rotation transforms are applied relative to the layer's anchor point
// this method moves a gesture recognizer's view's anchor point between the user's fingers
- (void)adjustAnchorPointForGestureRecognizer:(UIGestureRecognizer *)gestureRecognizer {
    if (gestureRecognizer.state == UIGestureRecognizerStateBegan) {
        UIView *piece = gestureRecognizer.view;
        CGPoint locationInView = [gestureRecognizer locationInView:piece];
        CGPoint locationInSuperview = [gestureRecognizer locationInView:piece.superview];

        piece.layer.anchorPoint = CGPointMake(locationInView.x / piece.bounds.size.width, locationInView.y / piece.bounds.size.height);
        piece.center = locationInSuperview;
    }
}

// scale the piece by the current scale
// reset the gesture recognizer's rotation to 0 after applying so the next callback is a delta from the current scale
- (void)scalePiece:(UIPinchGestureRecognizer *)gestureRecognizer
{
    [self adjustAnchorPointForGestureRecognizer:gestureRecognizer];

    if ([gestureRecognizer state] == UIGestureRecognizerStateBegan || [gestureRecognizer state] == UIGestureRecognizerStateChanged) {
        [gestureRecognizer view].transform = CGAffineTransformScale([[gestureRecognizer view] transform], [gestureRecognizer scale], [gestureRecognizer scale]);
        [gestureRecognizer setScale:1];
    }
}