以顶部中心为锚点缩放 UIView? [英] Scale UIView with the top center as the anchor point?

问题描述

我正在使用 CGAffineTransformMakeScale 缩放 UIView，但我想在缩放时将其锚定到当前的顶部中心点.

I'm scaling a UIView with CGAffineTransformMakeScale but I want to keep it anchored to it's current top center point as it's scaled.

我已经研究过设置 view.layer.anchorPoint 但我相信我需要将它与设置 view.layer.position 结合使用以说明更改在锚点.

I've looked into setting view.layer.anchorPoint but I believe I need to use this in conjunction with setting view.layer.position to account for the change in the anchor point.

如果有人能指出我正确的方向，我将不胜感激！

If anyone could point me in the right direction I'd be very grateful!

推荐答案

看看我在这里的回答，了解为什么当你改变锚点时你的视图会移动:https://stackoverflow.com/a/12208587/77567

Take a look at my answer here to understand why your view is moving when you change the anchor point: https://stackoverflow.com/a/12208587/77567

因此，从您的视图转换设置为身份开始.当视图未变换时，找到其顶边的中心:​​

So, start with your view's transform set to identity. When the view is untransformed, find the center of its top edge:

CGRect frame = view.frame;
CGPoint topCenter = CGPointMake(CGRectGetMidX(frame), CGRectGetMinY(frame));

然后锚点指向上边缘的中间:

Then the anchor point to the middle of the top edge:

view.layer.anchorPoint = CGPointMake(0.5, 0);

现在图层的position(或视图的center)是图层顶部边缘的中心位置.如果您停在此处，图层将移动，使其顶部边缘的中心位于更改锚点之前的真实中心位置.因此，将图层的 position 更改为刚才的顶部边缘的中心:

Now the layer's position (or the view's center) is the position of the center of the layer's top edge. If you stop here, the layer will move so that the center of its top edge is where its true center was before changing the anchor point. So change the layer's position to the center of its top edge from a moment ago:

view.layer.position = topCenter;

现在图层保持在屏幕上的同一位置，但它的锚点是其上边缘的中心，因此缩放和旋转将保持该点固定.

Now the layer stays in the same place on screen, but its anchor point is the center of its top edge, so scales and rotations will leave that point fixed.

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