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Unity Engine

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Unity Engine

Navigation events

Events that occur when the user navigates through the UI.
阅读时间3 分钟最后更新于 1 个月前
Navigation events occur at runtime when the user presses the D-pad, moves a joystick, or presses the 
Escape
, 
Enter
or arrow keys. They're an indicator that the user is trying to navigate the UI, but they're not limited to a specific input device, such as a keyboard. The difference from a Focus event is that the navigation event doesn't require the focus to move to a new UI element.
The base class for all navigation events is NavigationEventBase.
All navigation events trickle down, bubble up, and are cancellable, but it's recommended to listen to these events during the bubble-up propagation phase. This is because navigation events are triggered by input events that might also be used to interact with individual controls. For example, a button will react to a press of the 
Enter
key with a button click, and it will cancel the 
NavigationSubmitEvent
. Listening to these events during the bubble-up phase makes sure that they're navigation events.
The following table describes the navigation events and their propagation phases:

Event

Description

Trickles down

Bubbles up

Cancellable

NavigationMoveEventSent when user makes a move input.YesYesYes
NavigationCancelEventSent when the user makes a cancel input.YesYesYes
NavigationSubmitEventSent when the user makes a submit input.YesYesYes

Event list

The 
NavigationMoveEvent
is sent when the user presses the D-pad, moves a joystick, or presses the arrow keys.
Some controls will use the arrow keys for their own functionality. For example, the ListView allows the user to select items using the up and down arrow keys. In this case, the control will cancel the 
NavigationMoveEvent
and the event won't enter the bubble-up phase.
direction
: The direction of the navigation. (
None
, 
Left
, 
Up
, 
Right
, 
Down
)
move
: The move vector. If the event was triggered by an analog axis input, like a joystick, this property gives access to the directional vector.
The 
NavigationCancelEvent
is triggered when the user cancels the current navigation action, such as by pressing the `Escape`` key on the keyboard. It's important to note that this event doesn't affect the currently focused element, which means that the UI element that had focus before the cancellation remains selected.
The 
NavigationSubmitEvent
is triggered when the user presses the submit button, such as by pressing the `Enter`` key on the keyboard.
If a control handles the event itself, it cancels the event, preventing it from entering the bubble-up phase. For example, a TextField that has the focus will stop the 
NavigationSubmitEvent
from bubbling up. On the other hand, a focusable Label or Image will allow the 
NavigationSubmitEvent
to bubble up to its parent elements, allowing them to handle the event if needed.

Example

The following code example shows how to register callbacks for navigation events in a runtime UI:
using UnityEngine;using UnityEngine.UIElements;public class MyNavigationHandler: MonoBehaviour {    void OnEnable() {        // Get a reference to the root visual element        var uiDocument = GetComponent < UIDocument > ();        var rootVisualElement = uiDocument.rootVisualElement;        // Register for navigation events        rootVisualElement.RegisterCallback < NavigationCancelEvent > (OnNavCancelEvent);        rootVisualElement.RegisterCallback < NavigationMoveEvent > (OnNavMoveEvent);        rootVisualElement.RegisterCallback < NavigationSubmitEvent > (OnNavSubmitEvent);    }    private void OnNavSubmitEvent(NavigationSubmitEvent evt) {        Debug.Log($"OnNavSubmitEvent {evt.propagationPhase}");    }    private void OnNavMoveEvent(NavigationMoveEvent evt) {        Debug.Log($"OnNavMoveEvent {evt.propagationPhase} - move {evt.move} - direction {evt.direction}");    }    private void OnNavCancelEvent(NavigationCancelEvent evt) {        Debug.Log($"OnNavCancelEvent {evt.propagationPhase}");    }}

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