ios 更改尺寸时如何强制重绘（drawRect）子视图？
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How Do I Force Redrawing (drawRect) of a SubView When it Changes Dimensions?
提问by dugla
I have a UIView that contains a row of subclasses of UIView. The subclass has overridden drawRect: and has set contentMode = UIViewContentModeRedraw.
我有一个 UIView，其中包含一行UIView. 子类已覆盖drawRect: 并已设置 contentMode = UIViewContentModeRedraw.
As the user squashes and stretches the parent container the child viewssquash and stretch. As the shape change occurs I would like to have drawRectcalled repeatedly to change the contents of the child views. So far I have been unsuccessful. What is the correct way to do this?
当用户child views挤压和拉伸父容器时，挤压和拉伸。随着形状发生变化，我想drawRect反复调用以更改child views. 到目前为止，我一直没有成功。这样做的正确方法是什么？
Cheers,
干杯，
Doug
道格
回答by Adam Wright
In Cocoa, you rarely (if ever) call drawRect - you just mark the region or view as needing update, and it will be scheduled for redrawing. This allows redraws for multiple invalidations to be collapsed together.
在 Cocoa 中，您很少（如果有的话）调用 drawRect - 您只需将区域或视图标记为需要更新，并且将安排重绘。这允许将多个失效的重绘折叠在一起。
For Cocoa Touch, you want either [view setNeedsDisplay], or setNeedsDisplayinRect:(CGRect)
对于 Cocoa Touch，您需要[view setNeedsDisplay]或setNeedsDisplayinRect:(CGRect)
回答by Pascal
You need to call [view setNeedsLayout], this should cause the subviews to receive a drawRect: call if the layout changes. I haven't tested this, however.
您需要调用 [view setNeedsLayout]，这应该会导致子视图在布局更改时收到 drawRect: 调用。不过，我还没有测试过。
回答by Stan
This solution is a little crazy, but it makes logical sense, and has a great visual result. I'm working with a NSLayoutManagerand a couple NSTextContainers, laying out text in two columns. Because I'm using multiple text containers (and I'm not sure I want multiple UITextView), I'm overriding the draw(rect: CGRect)method of MyDrawingView: UIView.
这个解决方案有点疯狂，但它合乎逻辑，并且具有很好的视觉效果。我正在处理一个NSLayoutManager和几个NSTextContainers，在两列中布置文本。因为我使用的多个文本容器（我不知道我要多UITextView），我重写draw(rect: CGRect)的方法MyDrawingView: UIView。
The problem is that using self.contentMode = .redrawstill results in some minor stretching on rotation--significant enough to be a deal-breaker.
问题是使用self.contentMode = .redraw仍然会导致轮换时出现一些轻微的拉伸 - 足以破坏交易。
I noticed that setting contentMode = .left, or even contentMode = .scaleAspectFitwas close to what I wanted, in terms of pixel-perfect rotation. But obviously, I wasn't getting the draw call I needed.
我注意到设置contentMode = .left，甚至contentMode = .scaleAspectFit在像素完美旋转方面接近我想要的。但很明显，我没有得到我需要的绘图调用。
So--I overrode layoutSubviews(), switched the contentModeto .scaleAspectFit, called super.layoutSubviews(), and then switched it back. :P
所以 - 我覆盖layoutSubviews()，切换contentMode到.scaleAspectFit，调用super.layoutSubviews()，然后将其切换回来。:P
override func layoutSubviews() {
self.contentMode = .scaleAspectFit
super.layoutSubviews()
self.contentMode = .redraw
}
It is...perfect.
这十分完美。
