display(_:)
Tells the delegate to implement the display process.
Declaration
optional func display(_ layer: CALayer)Parameters
- layer:
The layer whose contents need updating.
Discussion
The display(_:) delegate method is called when the layer is marked for its content to be reloaded, typically initiated by the setNeedsDisplay() method. The typical technique for updating is to set the layer’s contents property.
The following code shows how you can create a class named LayerDelegate that implements CALayerDelegate and sets it as a layer’s (named sublayer) delegate. When setNeedsDisplay() is called on sublayer, the delegate’s display(_:) replaces its contents with a specified image.
let delegate = LayerDelegate()
lazy var sublayer: CALayer = {
let layer = CALayer()
layer.delegate = self.delegate
return layer
}()
// When `sublayer.setNeedsDisplay()` is called, `sublayer.contents` are updated.
class LayerDelegate: NSObject, CALayerDelegate {
func display(_ layer: CALayer) {
layer.contents = UIImage(named: "rabbit.png")?.cgImage
}
}