delegate property Null safety
The delegate used to draw the image representing the child.
Implementation
RasterWidgetDelegate get delegate => _delegate;Implementation
set delegate(RasterWidgetDelegate value) {
  if (value == delegate) {
    return;
  }
  delegate.removeListener(markNeedsPaint);
  final RasterWidgetDelegate oldDelegate = _delegate;
  _delegate = value;
  if (attached) {
    delegate.addListener(markNeedsPaint);
    if (delegate.shouldRepaint(oldDelegate)) {
      markNeedsPaint();
    }
  }
}