呈现为.OverCurrentContext的UIViewController呈现为.CrossDissolve不透明

Question

I am trying to get the familiar "translucent overlay" effect. I am using the .OverCurrentContext presentation style, and the presented VC has a view with 0.5 alpha, set in storyboard.

When I use the (default) transition of .CoverVertical, all is good. When I use .CrossDissolve (which is what I want) the presented view is opaque. When I check the presented view's alpha, it has somehow become 1. Why? Where do I intercede to prevent this?

let vc = self.storyboard!.instantiateViewControllerWithIdentifier("Overlay")!
vc.modalPresentationStyle = .OverCurrentContext
vc.modalTransitionStyle = .CrossDissolve
self.presentViewController(vc, animated:true, completion:nil)

Answer 1

Where do I intercede to prevent this?

You intercede in the whole animation. You're going to have to do a custom transition animation for your view controller presentation, because what you want to do is not covered by any of the four or five standard animations.