hitTestChildren method Null safety
- BoxHitTestResult result,
- {required Offset position}
Override this method to check whether any children are located at the given position.
Subclasses should return true if at least one child reported a hit at the specified position.
Typically children should be hit-tested in reverse paint order so that hit tests at locations where children overlap hit the child that is visually "on top" (i.e., paints later).
The caller is responsible for transforming position from global
coordinates to its location relative to the origin of this RenderBox.
Likewise, this RenderBox is responsible for transforming the position
that it passes to its children when it calls hitTest on each child.
If transforming is necessary, BoxHitTestResult.addWithPaintTransform,
BoxHitTestResult.addWithPaintOffset, or
BoxHitTestResult.addWithRawTransform need to be invoked by subclasses to
record the required transform operations in the BoxHitTestResult. These
methods will also help with applying the transform to position.
Used by hitTest. If you override hitTest and do not call this function, then you don't need to implement this function.
Implementation
@override
bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
final List<RenderBox> children = getChildrenAsList();
for (int i = _lastPaintOrder.length - 1; i >= 0; --i) {
final int childIndex = _lastPaintOrder[i];
if (childIndex >= children.length) {
continue;
}
final RenderBox child = children[childIndex];
final FlowParentData childParentData = child.parentData! as FlowParentData;
final Matrix4? transform = childParentData._transform;
if (transform == null) {
continue;
}
final bool absorbed = result.addWithPaintTransform(
transform: transform,
position: position,
hitTest: (BoxHitTestResult result, Offset position) {
return child.hitTest(result, position: position);
},
);
if (absorbed) {
return true;
}
}
return false;
}