updateCompositedLayer method Null safety
- {required covariant OpacityLayer? oldLayer}
Update the composited layer owned by this render object.
This method is called by the framework when isRepaintBoundary is true.
If oldLayer is null, this method must return a new OffsetLayer
(or subtype thereof). If oldLayer is not null, then this method must
reuse the layer instance that is provided - it is an error to create a new
layer in this instance. The layer will be disposed by the framework when
either the render object is disposed or if it is no longer a repaint
boundary.
The OffsetLayer.offset property will be managed by the framework and must not be updated by this method.
If a property of the composited layer needs to be updated, the render object must call markNeedsCompositedLayerUpdate which will schedule this method to be called without repainting children. If this widget was marked as needing to paint and needing a composited layer update, this method is only called once.
Implementation
@override
OffsetLayer updateCompositedLayer({required covariant OpacityLayer? oldLayer}) {
final OpacityLayer updatedLayer = oldLayer ?? OpacityLayer();
updatedLayer.alpha = _alpha;
return updatedLayer;
}