带有自定义CALayer的层支持的NSView不调用updateLayer吗? [英] Layer backed NSView with custom CALayer not calling updateLayer?

问题描述

我有一个自定义的支持图层的NSView，并且覆盖了makeBackingLayer方法以返回一个自定义的CALayer子类.我还覆盖了wantUpdateUpdateLayer返回true，从而完全选择了类似图层的绘图.

I have a custom layer-backed NSView and have overidden the makeBackingLayer method to return a custom CALayer subclass. I have also overriden wantsUpdateLayer to return true thereby fully opting into layer-like drawing.

override func makeBackingLayer() -> CALayer {
    return Layer() // my custom class with "drawLayer:" implemented
}

override var wantsUpdateLayer:Bool{
    return true
}

// never called
override func updateLayer() {
    super.updateLayer()
    println("updateLayer after")
    self.layer?.borderWidth += 1
}

执行完此操作后，我发现设置NSView.needsDisplay = true会将调用路由到自定义层的drawInContext:方法，而不是updateLayer:方法. 为什么这样做?在我的示例中，我检查了是否删除了makeBackingLayer覆盖，然后按预期方式调用了updateLayer.

Once I do this, I find that when I set NSView.needsDisplay = true it routes calls to the custom layer's drawInContext: method as opposed to the updateLayer: method. Why does it do this? In my example, I have checked that if I remove the makeBackingLayer override then my updateLayer is called in the expected manner.

我不太愿意指责它，但是其他实例则指出了这样一个概念，即当您的makeBackingLayer returns a custom CALayer`时，您实际上已将自定义层托管在父级支持层中. (纯粹是我的猜测)

I can't quite put my finger on it, but other instances point to the notion that when your makeBackingLayerreturns a customCALayer` that you actually have your custom layer hosted inside a parent backing layer. (Pure Speculation on my part)

此外，考虑到CALayer的drawInContext:更低级"，两条绘制路线之间会有不同的性能特征吗?有关此问题的更多详细信息，请参见此SO问题: Layer支持的NSView性能，可直接在CALayer.drawInContext中进行渲染:

Further, would there be different performance characteristics between the two drawing routes given that CALayer's drawInContext: is more "low-level"? See this SO question for more detail on that question: Layer-backed NSView performance with rendering directly in CALayer.drawInContext:

任何见识将不胜感激.

Any insight would be greatly appreciated.

推荐答案

您现在肯定已经解决了，但是对于以后的读者，我通过阅读

Surely you fixed it by now, but for future readers I found a possible explanation by reading the NSView documentation!

如果canDrawSubviewsIntoLayer属性设置为YES，则视图 忽略此方法返回的值.相反，视图总是 使用其drawRect:方法绘制其内容.

If the canDrawSubviewsIntoLayer property is set to YES, the view ignores the value returned by this method. Instead, the view always uses its drawRect: method to draw its content.

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