The following standard controls are built into UI Toolkit:
Contextual menus show a set of choices or actions to the user, depending on the context. This context can refer to anything, is usually the current selection.
To enable contextual menus, attach the ContextualMenuManipulator
manipulator to a visual element. This manipulator will display a contextual menu after either a right button mouse up event, or a menu key up event. The ContextualMenuManipulator
manipulator also adds a callback that responds to a ContextualMenuPopulateEvent
. The following code example shows how to do this:
void InstallManipulator(VisualElement element)
{
ContextualMenuManipulator m = new ContextualMenuManipulator(MyDelegate);
m.target = element;
}
void MyDelegate(ContextualMenuPopulateEvent event)
{
// Modify event.menu
event.menu.AppendAction("Properties", DisplayProperties, DropdownMenu.MenuAction.AlwaysEnabled);
}
void DisplayProperties(DropdownMenu.MenuAction menuItem)
{
// ...
}
The callback given to the ContextualMenuManipulator
constructor is invoked last so children elements can populate the menu.
Internally the manipulator sends a ContextualMenuPopulateEvent
event that is propagated to the target element hierarchy, along the propagation path: from the root of the visual tree to the event target, then back up the visual tree to the root. Along the propagation path, the elements with a callback for the ContextualMenuPopulateEvent
event can add, remove, or modify items in the contextual menu.
When an element receives a ContextualMenuPopulateEvent
, it adds menu items to the contextual menu by calling either DropdownMenu.InsertAction()
or DropdownMenu.AppendAction()
.
Each of these functions take two callbacks as parameters. The first callback is executed when the user selects the item in the menu. The second callback is executed before displaying the menu and also checks whether the menu item is enabled.
Both callbacks receive a MenuAction
as a parameter. The MenuAction
represents the menu item and has the following other useful properties:
MenuAction.userData
contains a reference to user data that might have been used with AppendAction()
or InsertAction()
.MenuAction.eventInfo
contains information about the event that triggered
the display of the contextual menu. Use MenuAction.eventInfo
in the action that responds to the event. For example, you can use the mouse position to create and place an object based on the selected contextual menu item.