A drop-down menu.
| DropdownMenu | Constructor. |
| AppendAction | Add an item that will execute an action in the drop-down menu. The item is added at the end of the current item list. |
| AppendSeparator | Add a separator line in the menu. The separator is added at the end of the current item list. |
| InsertAction | Add an item that will execute an action in the drop-down menu. The item is added at the end of the specified index in the list. |
| InsertSeparator | Add a separator line in the menu. The separator is added at the end of the specified index in the list. |
| MenuItems | Get the list of menu items. |
| PrepareForDisplay | Update the status of all items by calling their status callback and remove the separators in excess. This is called just before displaying the menu. |
| RemoveItemAt | Remove the menu item at index. |