在调整视图大小之前，不会显示新的 CALayer.contents
我有一个 CALayer 需要显示视频帧。每次渲染一帧（作为CGImageRef）时，都会调用此方法：
- (void)displayFrame:(CGImageRef)frame {
[view layer].contents = (id)frame;
}
奇怪的是，它首先不会显示任何内容。每次调整 view 大小时，都会显示一个新的 frame，但会一直保留到再次调整 view 大小为止。
我该如何解决这个问题？
I have a CALayer that needs to display frames of video. Every time a frame is rendered (as a CGImageRef), this method is called:
- (void)displayFrame:(CGImageRef)frame {
[view layer].contents = (id)frame;
}
What's strange is that this, at first, will not display anything. Every time view is resized, a new frame is displayed, but sticks until view is resized again.
How do I fix this?
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displayFrame: 是否在主线程上被调用？如果没有，那么我发现它不会总是绘制。您可以尝试使用 [CATransactionlush] 强制其更新，例如：
如果这不起作用，那么您可以尝试包含图层构造代码以帮助识别该图层的任何特殊性。
Is displayFrame: being called on the main thread? If not then I have found that it will not always draw. You can try forcing it to update by using [CATransaction flush] like:
If that does not work then you might try including the layer construction code to help identify any peculiarities with this layer.
您可能需要执行
[[view layer] setNeedsDisplay]。需要通知绘图系统已进行更新并且需要重新绘制屏幕。调整视图大小可以做到这一点，但更改图层的内容似乎可能不会。You probably need to do
[[view layer] setNeedsDisplay]. The drawing system needs to be informed that updates have been made and the screen needs to be repainted. Resizing a view does this, but it seems that changing a layer'scontentsmight not.使用
[CATransactionlush];为我解决了这个问题。我必须弄清楚使用这种方法显示文本对性能有何影响（如果有）。Using
[CATransaction flush];did the trick for me. I have to figure out what (if any) performance hit I take for displaying text using this approach.