Swift version: 5.1
iOS can dynamically generate shadows for any
UIView, and these shadows automatically adjust to fit the shape of the item in question – even following the curves of text inside a
UILabel. This functionality is built right in, so all you need to do is configure its properties, and there are four you need to care about:
shadowColorsets the color of the shadow, and needs to be a
shadowOpacitysets how transparent the shadow is, where 0 is invisible and 1 is as strong as possible.
shadowOffsetsets how far away from the view the shadow should be, to give a 3D offset effect.
shadowRadiussets how wide the shadow should be.
Here's a simple example to get you started:
let yourView = UIView() yourView.layer.shadowColor = UIColor.black.cgColor yourView.layer.shadowOpacity = 1 yourView.layer.shadowOffset = .zero yourView.layer.shadowRadius = 10
Be warned: generating shadows dynamically is expensive, because iOS has to draw the shadow around the exact shape of your view's contents. If you can, set the
shadowPath property to a specific value so that iOS doesn't need to calculate transparency dynamically. For example, this creates a shadow path equivalent to the frame of the view:
yourView.layer.shadowPath = UIBezierPath(rect: yourView.bounds).cgPath
Alternatively, ask iOS to cache the rendered shadow so that it doesn't need to be redrawn:
yourView.layer.shouldRasterize = true
If you want to go down the rasterization route, you should make sure iOS caches the shadow at the same drawing scale as the main screen, otherwise it will look pixelated:
yourView.layer.rasterizationScale = UIScreen.main.scale
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Available from iOS 3.2
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
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