---
title: "display(_:)"
framework: quartzcore
role: symbol
role_heading: Instance Method
path: "quartzcore/calayerdelegate/display(_:)"
---

# display(_:)

Tells the delegate to implement the display process.

## Declaration

```swift
optional func display(_ layer: CALayer)
```

## Parameters

- `layer`: The layer whose contents need updating.

## Discussion

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     } }

## See Also

### Providing the Layer’s Content

- [draw(_:in:)](quartzcore/calayerdelegate/draw(_:in:).md)
- [layerWillDraw(_:)](quartzcore/calayerdelegate/layerwilldraw(_:).md)