iOS controlling UIView alpha behaviour for subview

问题:

In my example, I have 3 views: one red view containing two white views. I change the red container view's alpha to 0.3 and this happens (look at the image, the current result).

By seeing this, I can only assume (tell me if I'm wrong) that setting a view's alpha will also set all of its subviews' alphas. My question is : is there a way to simply tell the red view to act as a whole so that setting its alpha would give something that looks like the wanted result (in the image)?

This is what it looks like without any alpha :

回答1:

Check out the possible UIKit keys for Info.plist, specifically UIViewGroupOpacity.

UIViewGroupOpacity (Boolean - iOS) specifies whether Core Animation sublayers inherit the opacity of their superlayer.

Info.plist UIKit Keys

回答2:

To elaborate on Mark's answer: If you set UIViewGroupOpacity in the Info.plist, it will change the behavior for all views in your app, if you are interested in only fixing the rendering of this particular view, you could also use this snippet:

redContainerView.layer.shouldRasterize = YES;
// No setting rasterizationScale, will cause blurry images on retina.
redContainerView.layer.rasterizationScale = [[UIScreen mainScreen] scale];

回答3:

IOS alpha property is inherited by its subviews . If we are setting alpha 0.3 for red view then both subview will have the alpha = 0.3. There is no way to stop subview to inherit alpha value from its super view .

The solution might be . You can set the colour of Red view with alpha 0.3. Color property will not inhered by its subview. Yor can use below code

    [redView setBackgroundColor:[UIColor colorWithHue:238.0f/255.0f saturation:24.0f/255.0f brightness:24.0f/255.0f alpha:0.3]];