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# isAsynchronous

Determines when the contents of the layer are updated.

```
var isAsynchronous: Bool { get set }
```

## Discussion

If <doc://com.apple.documentation/documentation/Swift/false>, the contents of the layer are updated only in response to receiving a [`setNeedsDisplay()`](/documentation/QuartzCore/CALayer/setNeedsDisplay()) message. When <doc://com.apple.documentation/documentation/Swift/true>, the receiver’s [`canDraw(inCGLContext:pixelFormat:forLayerTime:displayTime:)`](/documentation/QuartzCore/CAOpenGLLayer/canDraw(inCGLContext:pixelFormat:forLayerTime:displayTime:)) is called periodically to determine if the OpenGL content should be updated.

## See Also

  [Core Animation Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/CoreAnimation_guide/Introduction/Introduction.html#//apple_ref/doc/uid/TP40004514)


---

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