iphone - 使用变换旋转，然后更改框架原点， View 会扩展？

Question

这就是 iPhone 的困境。我正在开发一个库，但已将我的问题缩小到非常简单的代码。此代码的作用是创建一个 50x50 View ，应用几度的旋转变换，然后将帧向下移动几次。结果是 50x50 View 现在看起来更大了。

代码如下:

// a simple 50x50 view
UIView *redThing = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 50, 50)];
redThing.backgroundColor = [UIColor redColor];

[self.view addSubview:redThing];

// rotate a small amount (as long as it's not 90 or 180, etc.)
redThing.transform = CGAffineTransformRotate(redThing.transform, 0.1234);

// move the view down 2 pixels
CGRect newFrame = CGRectMake(redThing.frame.origin.x, redThing.frame.origin.y + 2, redThing.frame.size.width, redThing.frame.size.height);
redThing.frame = newFrame;

// move the view down another 2 pixels
newFrame = CGRectMake(redThing.frame.origin.x, redThing.frame.origin.y + 2, redThing.frame.size.width, redThing.frame.size.height);
redThing.frame = newFrame;

// move the view down another 2 pixels
newFrame = CGRectMake(redThing.frame.origin.x, redThing.frame.origin.y + 2, redThing.frame.size.width, redThing.frame.size.height);
redThing.frame = newFrame;

// move the view down another 2 pixels
newFrame = CGRectMake(redThing.frame.origin.x, redThing.frame.origin.y + 2, redThing.frame.size.width, redThing.frame.size.height);
redThing.frame = newFrame;

那么，这到底是怎么回事？现在，如果我通过应用平移变换来移动 View ，它就可以正常工作。但这不是我想要做的，无论如何这应该有效。

有什么想法吗？

Answer 1

来自 UIView 文档:

If the transform property is also set, use the bounds and center properties instead; otherwise, animating changes to the frame property does not correctly reflect the actual location of the view.

Warning: If the transform property is not the identity transform, the value of this property is undefined and therefore should be ignored.

换句话说，当设置 transform 时，我会对 frame 属性保持警惕。