How to draw custom views in Interface Builder using IBDesignable

Swift version: 5.10

Paul Hudson @twostraws May 28th 2019

You've always been able to have custom views inside your apps, but if you're having a hard time visualizing how they look at design time then you should try @IBDesignable: it lets you see exactly how your custom views look inside IB, and if you combine it with @IBInspectable you can even adjust your view's design there too.

This example view draws an ellipse that fills itself. If you add this to your project, create a view, then set that view to have this custom subclass, you'll see an ellipse appear immediately. You can move the view or resize it, and the ellipse will be updated. Plus, because I used @IBInspectable you can adjust the colors and stroke width right inside the attributes inspector, helping you make sure your UI looks exactly as you expect.

@IBDesignable class EllipseView: UIView {
    @IBInspectable var strokeWidth: CGFloat = 0
    @IBInspectable var fillColor: UIColor = UIColor.black
    @IBInspectable var strokeColor: UIColor = UIColor.clear

    override func draw(_ rect: CGRect) {
        guard let context = UIGraphicsGetCurrentContext() else { return }
        let rectangle = bounds.insetBy(dx: strokeWidth / 2, dy: strokeWidth / 2)

        context.setFillColor(fillColor.cgColor)
        context.setStrokeColor(strokeColor.cgColor)
        context.setLineWidth(strokeWidth)

        context.addEllipse(in: rectangle)
        context.drawPath(using: .fillStroke)
    }
}