How to render example content using prepareForInterfaceBuilder()
Swift version: 5.4
Whenever you create a custom UIView subclass using @IBDesignable, it’s usually a good idea to provide it with some sample content so it can render meaningfully at design time.
For example, here’s a simple ShapeView class that renders a UIBezierPath inside a view, using CAShapeLayer:
@IBDesignable class ShapeView: UIView {
@IBInspectable var strokeColor: UIColor = UIColor.black
@IBInspectable var fillColor: UIColor = UIColor.clear
var path: UIBezierPath?
override class var layerClass: AnyClass {
return CAShapeLayer.self
}
override func layoutSubviews() {
guard let layer = layer as? CAShapeLayer else { return }
layer.path = path?.cgPath
layer.strokeColor = strokeColor.cgColor
layer.fillColor = fillColor.cgColor
}
}While that might work well enough at runtime, you won’t be able to see anything when used with Interface Builder because it relies on a bezier path being set. So, while you can adjust the stroke and fill colors all you want, you can’t see how those changes look.
To fix this, Xcode lets us add a special method in the view called prepareForInterfaceBuilder(). If present, this is called by Interface Builder when your custom view is being drawn, and it’s your chance to provide some example content so others can see how it looks.
In this instance, setting the path property to a default shape does the job neatly:
override func prepareForInterfaceBuilder() {
let drawRect = CGRect(x: 0, y: 0, width: 128, height: 128)
path = UIBezierPath(rect: drawRect)
}This method is only called at design time, so you don’t have to worry about it being run in shipping code.
SPONSORED Join a FREE crash course for iOS devs who want to become complete senior developers — from October 18th to 24th. Learn how to apply iOS app architecture patterns through a series of lectures and practical coding sessions.
Sponsor Hacking with Swift and reach the world's largest Swift community!
Available from iOS
Similar solutions…
- How to render Markdown content in text
- How to render shadows using NSShadow and setShadow()
- How to render images using SF Symbols
- How to render a gradient
- How to made an SKSpriteNode render faster using blendMode
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
