Transparency gradient on UIImageView
objective-c, uiimage, uiimageview
Solution
The easiest way to do this is to use a CAGradientLayer as a layer mask—in other words, use its opacity to determine the opacity of the layer it’s attached to. Something along these lines should do the trick:
CALayer *imageViewLayer = theImageView.layer;
CAGradientLayer *maskLayer = [CAGradientLayer layer];
maskLayer.colors = @[ (id)([UIColor blackColor].CGColor), (id)([UIColor clearColor].CGColor) ]; // gradient from 100% opacity to 0% opacity (non-alpha components of the color are ignored)
// startPoint and endPoint (used to position/size the gradient) are in a coordinate space from the top left to bottom right of the layer: (0,0)–(1,1)
maskLayer.startPoint = CGPointMake(0, 0.5); // middle left
maskLayer.endPoint = CGPointMake(0, 0); // top left
maskLayer.frame = imageViewLayer.bounds; // line it up with the layer it’s masking
imageViewLayer.mask = maskLayer;
Problem
I would imagine what I am trying to do is quite simple, but I can't seem to figure it out. I know how to apply a gradient on a `UIImage` using an `UIImageView`, but that is not what I want. What I want to do is, while keeping the image bounds, is to fade out the top half of a `UIImage` so it is fully transparent. I want to be able to see the view behind the `UIImage` with the bottom half of the image still fully visible (not opaque). Any ideas? Any help would be greatly appreciated.