问题:

I am writing a UI library in which i would like to be able to have the alpha of the UIViews as if the UIViewGroupOpacity info.plist ket was set. See following links:

Make UIView and subviews translucent as one layer, not individually

iOS controlling UIView alpha behaviour for subviews

But, as I am writing a lib, I dont want the projects to have to set this global key, and effect the behaviour of the main project.

Is there any other way of achieving this? I dont want to cycle through all the subviews and set alpha of each subview, as the project that includes my lib might have this key enabled...

回答1:

Yes there is, you can set shouldRasterize of the view's layer.

containerView.layer.shouldRasterize = YES;
// Not setting rasterizationScale, will cause blurry images on retina displays:
containerView.layer.rasterizationScale = [[UIScreen mainScreen] scale];

This will have the same effect as UIViewGroupOpacity but only for containerView and it's subviews.

回答2:

For iOS 7.0 and later:

Since iOS 7.0, this can be controlled for each CALayer individually through the allowsGroupOpacity property. By setting it to YES, you get the same behavior as if UIViewGroupOpacity was set, but just for that particular layer.