DropdownMenuDescriptor.expansion

Description

Displays a submenu in a new contextual menu next to the parent item.

Otherwise, submenus display in the same menu as their parent item, override the previous options in the submenu, and create a back button in the title area.

using UnityEditor;
using UnityEditor.UIElements;
using UnityEngine;
using UnityEngine.UIElements;

public class ContextMenuWindow : EditorWindow
{
    [MenuItem("My/Context Menu Window")]
    static void ShowMe() => GetWindow<ContextMenuWindow>();

    void CreateGUI()
    {
        var contextMenuContainer = new VisualElement();
        contextMenuContainer.style.flexGrow = 1;
        contextMenuContainer.AddManipulator(new ContextualMenuManipulator(e =>
        {
            e.menu.SetDescriptor(new DropdownMenuDescriptor()
            {
                allowSubmenus = true,
                expansion = true,
            });

            e.menu.AppendAction("Submenu/Action 1", a => Debug.Log("Action 1 Works"), DropdownMenuAction.AlwaysEnabled);
        }));

        rootVisualElement.Add(contextMenuContainer);
    }
}