insert method
Insert Grid Item to update itemList, and render DragGrid
Implementation
void insert({int index = 0, required T item, bool animation = true}) {
if (index < 0) {
index = itemList.length + index;
}
if (index >= 0 && index < _itemList.length) {
_itemList.removeWhere((opt) => opt == item);
_itemList.insert(index, item);
_animation = animation;
notifyListeners();
}
}