addChildAt method
Implementation
@override
void addChildAt(Bitmap child, int index) {
if (index < 0 || index > _children.length) {
throw ArgumentError('The supplied index is out of bounds.');
} else if (child.parent == this) {
_addLocalChildAt(child, index);
} else {
child.removeFromParent();
_children.insert(index, child);
child._parent = this;
}
}