paintChild method Null safety
override
Paint the i
th child using the given transform.
The child will be painted in a coordinate system that concatenates the container's coordinate system with the given transform. The origin of the parent's coordinate system is the upper left corner of the parent, with x increasing rightward and y increasing downward.
The container will clip the children to its bounds.
Implementation
@override
void paintChild(int i, { Matrix4? transform, double opacity = 1.0 }) {
transform ??= Matrix4.identity();
final RenderBox child = _randomAccessChildren[i];
final FlowParentData childParentData = child.parentData! as FlowParentData;
assert(() {
if (childParentData._transform != null) {
throw FlutterError(
'Cannot call paintChild twice for the same child.\n'
'The flow delegate of type ${_delegate.runtimeType} attempted to '
'paint child $i multiple times, which is not permitted.',
);
}
return true;
}());
_lastPaintOrder.add(i);
childParentData._transform = transform;
// We return after assigning _transform so that the transparent child can
// still be hit tested at the correct location.
if (opacity == 0.0) {
return;
}
void painter(PaintingContext context, Offset offset) {
context.paintChild(child, offset);
}
if (opacity == 1.0) {
_paintingContext!.pushTransform(needsCompositing, _paintingOffset!, transform, painter);
} else {
_paintingContext!.pushOpacity(_paintingOffset!, ui.Color.getAlphaFromOpacity(opacity), (PaintingContext context, Offset offset) {
context.pushTransform(needsCompositing, offset, transform!, painter);
});
}
}