public static class ElementAdderMenuBuilder

public static class ElementAdderMenuBuilder

public class ShoppingListElementAdder : IElementAdder<ShoppingList> {
    public ShoppingListElementAdder(ShoppingList shoppingList) {
        Object = shoppingList;
    }

    public ShoppingList Object { get; private set; }

    public bool CanAddElement(Type type) {
        return true;
    }
    public object AddElement(Type type) {
        var instance = Activator.CreateInstance(type);
        shoppingList.Add((ShoppingItem)instance);
        return instance;
    }
}

private void DrawAddMenuButton(ShoppingList shoppingList) {
    var content = new GUIContent("Add Menu");
    Rect position = GUILayoutUtility.GetRect(content, GUI.skin.button);
    if (GUI.Button(position, content)) {
        var builder = ElementAdderMenuBuilder.For<ShoppingList>(ShoppingItem);
        builder.SetElementAdder(new ShoppingListElementAdder(shoppingList));
        var menu = builder.GetMenu();
        menu.DropDown(buttonPosition);
    }
}

public class ShoppingListElementAdder extends IElementAdder.<ShoppingList> {
    var _object:ShoppingList;

    function ShoppingListElementAdder(shoppingList:ShoppingList) {
        Object = shoppingList;
    }

    function get Object():ShoppingList { return _object; }

    function CanAddElement(type:Type):boolean {
        return true;
    }
    function AddElement(type:Type):System.Object {
        var instance = Activator.CreateInstance(type);
        shoppingList.Add((ShoppingItem)instance);
        return instance;
    }
}

function DrawAddMenuButton(shoppingList:ShoppingList) {
    var content = new GUIContent('Add Menu');
    var position = GUILayoutUtility.GetRect(content, GUI.skin.button);
    if (GUI.Button(position, content)) {
        var builder = ElementAdderMenuBuilder.For.<ShoppingList>(ShoppingItem);
        builder.SetElementAdder(new ShoppingListElementAdder(shoppingList));
        var menu = builder.GetMenu();
        menu.DropDown(buttonPosition);
    }
}