ios - 如何防止 View 在捏合手势上超出其父边界 - swift

Question

我将捏合手势分配给了 uiview:

myView.addGestureRecognizer(UIPinchGestureRecognizer(target: self, action: "handlePinch:"))

此函数将缩放 uiview:

func handlePinch(recognizer : UIPinchGestureRecognizer) {
    if let view = recognizer.view {
      view.transform = CGAffineTransformScale(view.transform, 
                                recognizer.scale, recognizer.scale)
      recognizer.scale = 1
    }
}

但比例在父 View 内不受限制。当我尝试缩小它时，它也没有限制，它会一直缩放直到消失。

灰色 View 是父 View

我的问题是

如何防止放大时超出父框架，缩小时消失？

Answer 1

你可以使用这样的东西:

if let view = recognizer.view, parent = recognizer.view.superview {

    // this will only let it scale to half size
    let minimumThreshold: CGFloat = 0.5
    var scale: CGFloat = recognizer.scale

    // assuming your view is square, which based on your example it is
    let newSize = view.frame.height * scale

    // prevents the view from growing larger than the smallest dimension of the parent view
    let allowableSize = min(parent.frame.height, parent.frame.width)
    let maximumScale: CGFloat = allowableSize/view.frame.height

    // change scale if it breaks either bound
    if scale < minimumThreshold {
        print("size is too small")
        scale = minimumThreshold
    }

    if newSize > allowableSize {
        print("size is too large")
        scale = maximumScale
    }

    // apply the transform
    view.transform = CGAffineTransformMakeScale(scale, scale)
}

此处的关键是根据偏好确定下限，并根据 View 的初始大小与父 View 大小的比率确定上限。通过这样做， View 不能缩小到比期望的更小，因为假设用户不应该能够缩小到由于难以捏合而无法调整大小的点。此外，不应允许 View 无限缩放，从而溢出其边界。此检查就是这样做的，因为它只允许您指定由用户交互设置的尺寸范围。