addSlot method
Implementation
void addSlot(T? item, {bool update = true}) {
final index = _relationship.length;
final Rect rect = calcSlotRect(index: index, layoutWidth: layoutWidth);
final slot = _createSlot(index: index, item: item, rect: rect);
final child = _createItem(index: index, item: item, rect: rect);
_relationship[slot] = child;
if (mounted && update) {
_updateSlots();
setState(() {});
widget.onChanged?.call(items);
}
}