Mouse events

Mouse events occur when you interact with the UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary using a mouse. Touch, pens, or other pointing devices generate other events, not mouse events. In the Mouse event APIs and in this documentation, the term “mouse” refers only to a physical mouse or a virtual mouse that emulates a physical mouse.

Mouse events are always preceded by the corresponding PointerEvent.

The base class for all mouse events is MouseEventBase.

Event	Description	Trickles down	Bubbles up	Cancellable
MouseDownEvent	Sent when the user presses a mouse button.	✔	✔	✔
MouseUpEvent	Sent when the user releases a mouse button.	✔	✔	✔
MouseMoveEvent	Sent when the user moves the mouse.	✔	✔	✔
WheelEvent	Sent when the user activates the mouse wheel.	✔	✔	✔
MouseEnterWindowEvent	Sent when the mouse enters a window.			✔
MouseLeaveWindowEvent	Sent when the mouse leaves a window.			✔
MouseEnterEvent	Sent when the mouse enters an element or one of its descendants.	✔		✔
MouseLeaveEvent	Sent when the mouse leaves an element or one of its descendants.	✔		✔
MouseOverEvent	Sent when the mouse enters an element.	✔	✔	✔
MouseOutEvent	Sent when the mouse leaves an element.	✔	✔	✔
ContextClickEvent (obsolete)	Sent when the user presses and releases the third mouse button. Exists for backwards compatibility with IMGUI.	✔	✔	✔

Unique Properties

button: The button property returns an integer that identifies the mouse button pressed to trigger an event. The following table lists the integer and associated mouse button:

Integer	Button
0	Left button
1	Right button
2	Middle button

pressedButtons: The pressedButton property returns an integer that identifies which combination of mouse buttons are currently pressed.

The number is the sum of the individual buttons’ integer value (see table below). For example, holding the right mouse button and the middle mouse button pressed at the same time will result in pressedButton having a value of 6.

Integer	Button
1	Left button
2	Right button
4	Middle button

modifiers: The modifiers property returns the modifier key pressed during a keyboard event. Some examples of modifiers are the Shift, Ctrl, or Alt keys.

For more information, see the Modifier keys section of the MDN documentation.

mousePosition: The mousePosition property returns the mouse position within the panel, also known as the screen coordinate system. For more information on panel coordinates, see the Visual Tree page.

localMousePosition: The localMousePosition property returns the coordinates relative to the target visual element.

mouseDelta: The difference between the pointer’s position during the previous mouse event and its position during the current mouse event.

Event list

The following list provides the name, description, and target of each event in the event family. For more information on the event, see the UI Toolkit API.

MouseDownEvent

A MouseDownEvent is sent when the mouse button is pressed while the cursor is inside a visual element.

target: The visual element that receives the mouse capture. Otherwise, it’s the topmost selectable element under the cursor.

MouseUpEvent

The MouseUpEvent triggers when a mouse button releases while the cursor is within a visual element. MouseUpEvent is complimentary to MouseDownEvent.

target: The visual element that receives the mouse capture. Otherwise, it’s the topmost selectable element under the cursor.

MouseMoveEvent

The MouseMoveEvent is sent when the cursor hotspot is moved within a visual element.

target: The visual element that receives the mouse capture. Otherwise, it’s the topmost selectable element under the cursor.

WheelEvent

The WheelEvent is sent when the mouse wheel is pressed.

target: The visual element that receives the mouse capture. Otherwise, it’s the topmost selectable element under the cursor.

MouseEnterWindowEvent

A MouseEnterWindowEvent triggers when the cursor is moved into an Editor window. Runtime panels don’t receive this event when you enter the Game view window.

target: The visual element that receives the mouse capture. Otherwise, it’s the topmost selectable element under the cursor.

MouseLeaveWindowEvent

MouseLeaveWindowEvent fires when the cursor exits the space of an Editor window. The MouseLeaveWindowEvent is the counterpoint to MouseEnterWindowEvent.

target: The visual element that receives the mouse capture. Otherwise it returns null, as the cursor isn’t over an element.

MouseEnterEvent

The MouseEnterEvent is sent when the cursor is moved into a visual element, or one of its descendants.

target: The visual element under the mouse cursor, or one of its descendants.

MouseLeaveEvent

MouseLeaveEvent triggers when the cursor moves outside of a visual element. This event differs from MouseOutEvent as this event is sent to each element the mouse exits. This event doesn’t propagate.

target: The visual element (or one of its descendants) that the mouse cursor exits.

MouseOverEvent

The MouseOverEvent is sent when the cursor enters an element. This differs from MouseEnterEvent, because this event is only sent to the entered element.

target: The visual element that’s under the mouse cursor.

MouseOutEvent

The MouseOutEvent triggers when a pointing device moves the cursor outside the boundary of a visual element.

MouseOutEvent is different from MouseLeaveEvent in that MouseOutEvent is sent when leaving the visual element to any other element, while MouseLeaveEvent isn’t sent when transitioning from a visual element to descendant elements.

target: The visual element that the mouse cursor exited.

ContextualMenuPopulateEvent

Event sent by the ContextualMenuManager when the contextual menu needs to be populated with menu items.

target: The visual element for which the contextual menu is being built.

ContextClickEvent (obsolete)

Event sent when the user presses and releases the third mouse button. This event only exists for backward compatibility with IMGUI.

Examples

Editor window example

The following code sample creates an Editor window with three buttons that prints messages to the console when the mouse moves over an element, or buttons are pressed on the mouse.

This code sample highlights the event firing of both MouseDownEvent and MouseEnterEvent, and how to use the event parameters.

To see the example in action, do the following:

1. Create a new C# script called MouseEventTestWindow
2. Copy the example into the C# script.
3. Open the example under Window > UI Toolkit > Mouse Event Test Window.

using UnityEditor;
using UnityEngine;
using UnityEngine.UIElements;

// Open this in the Editor via the menu Window --> UI ToolKit --> Mouse Event Test Window
public class MouseEventTestWindow : EditorWindow

{​
    [MenuItem("Window/UI Toolkit/Mouse Event Test Window")]

    public static void ShowExample()

    {​
        MouseEventTestWindow wnd = GetWindow<MouseEventTestWindow>();
        wnd.titleContent = new GUIContent("Mouse Event Test Window");
    }

    public void CreateGUI()

    {​
        // Add a few buttons
        for (int i = 0; i < 3; i++)
        {​
            Button newElement = new Button {​ name = $"Button {​i}", text = $"Button {​i}" };
            newElement.style.flexGrow = 1;
            rootVisualElement.Add(newElement);
        }
        // Register mouse event callbacks
        rootVisualElement.RegisterCallback<MouseDownEvent>(OnMouseDown, TrickleDown.TrickleDown);
        rootVisualElement.RegisterCallback<MouseEnterEvent>(OnMouseEnter, TrickleDown.TrickleDown);
    }


    private void OnMouseDown(MouseDownEvent evt)

    {​
        bool leftMouseButtonPressed = 0 != (evt.pressedButtons & (1 << (int)MouseButton.LeftMouse));
        bool rightMouseButtonPressed = 0 != (evt.pressedButtons & (1 << (int)MouseButton.RightMouse));
        bool middleMouseButtonPressed = 0 != (evt.pressedButtons & (1 << (int)MouseButton.MiddleMouse));
        Debug.Log($"Mouse Down event. Triggered by {​(MouseButton)evt.button}.");
        Debug.Log($"Pressed buttons: Left button: {​leftMouseButtonPressed} Right button: {​rightMouseButtonPressed} Middle button: {​middleMouseButtonPressed}");
    }


    private void OnMouseEnter(MouseEnterEvent evt)

    {​
        VisualElement targetElement = (VisualElement)evt.target;
        Debug.Log($"Mouse is now over element '{​targetElement.name}'");
    }

}

Runtime example

The following code sample prints messages to the console when any mouse buttons are pressed, showing which button triggered the event, and which buttons are currently pressed.

This code sample highlights registering a callback to the MouseDownEvent and how to use the event parameters. To see the example in action, do the following:

1. Create a GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
   See in Glossary with a valid UIDocument.
2. Under Assets > Scripts, create a C# script called MouseEventTestRuntime.
3. Copy the example into the C# script.
4. Attach the MouseEventTestRuntime script to the GameObject with the UIDocument.
5. Enter Play mode.
6. Move the mouse over the game view and press or hold buttons on the mouse.

using UnityEngine;
using UnityEngine.UIElements;

public class MouseEventTestRuntime : MonoBehaviour
{
    void Start()
    {
        var root = GetComponent<UIDocument>().rootVisualElement;
        var newLabel = new Label("Move the mouse or press buttons to see the log output");
        newLabel.style.flexGrow = 1;
        root.Add(newLabel);
        root.RegisterCallback<MouseDownEvent>(OnMouseDown, TrickleDown.TrickleDown);
    }

    private void OnMouseDown(MouseDownEvent evt)
    {
        bool leftMouseButtonPressed = 0 != (evt.pressedButtons & (1 << (int)MouseButton.LeftMouse));
        bool rightMouseButtonPressed = 0 != (evt.pressedButtons & (1 << (int)MouseButton.RightMouse));
        bool middleMouseButtonPressed = 0 != (evt.pressedButtons & (1 << (int)MouseButton.MiddleMouse));

        VisualElement targetElement = (VisualElement)evt.target;
        Debug.Log($"Mouse Down event. Triggered by {(MouseButton)evt.button} over element '{targetElement.name}'");
        Debug.Log($"Pressed buttons: Left button: {leftMouseButtonPressed} Right button: {rightMouseButtonPressed} Middle button: {middleMouseButtonPressed}");
    }
}