move method

Implementation

@override
void move(RenderBox child, { RenderBox? after }) {
  // There are two scenarios:
  //
  // 1. The child is not keptAlive.
  // The child is in the childList maintained by ContainerRenderObjectMixin.
  // We can call super.move and update parentData with the new slot.
  //
  // 2. The child is keptAlive.
  // In this case, the child is no longer in the childList but might be stored in
  // [_keepAliveBucket]. We need to update the location of the child in the bucket.
  final SliverMultiBoxAdaptorParentData childParentData = child.parentData! as SliverMultiBoxAdaptorParentData;
  if (!childParentData.keptAlive) {
    super.move(child, after: after);
    childManager.didAdoptChild(child); // updates the slot in the parentData
    // Its slot may change even if super.move does not change the position.
    // In this case, we still want to mark as needs layout.
    markNeedsLayout();
  } else {
    // If the child in the bucket is not current child, that means someone has
    // already moved and replaced current child, and we cannot remove this child.
    if (_keepAliveBucket[childParentData.index] == child) {
      _keepAliveBucket.remove(childParentData.index);
    }
    assert(() {
      _debugDanglingKeepAlives.remove(child);
      return true;
    }());
    // Update the slot and reinsert back to _keepAliveBucket in the new slot.
    childManager.didAdoptChild(child);
    // If there is an existing child in the new slot, that mean that child will
    // be moved to other index. In other cases, the existing child should have been
    // removed by updateChild. Thus, it is ok to overwrite it.
    assert(() {
      if (_keepAliveBucket.containsKey(childParentData.index)) {
        _debugDanglingKeepAlives.add(_keepAliveBucket[childParentData.index]!);
      }
      return true;
    }());
    _keepAliveBucket[childParentData.index!] = child;
  }
}