A panel represents a visible instance of a UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary hierarchy. It handles element behavior event dispatching within the hierarchy of the visual treeAn object graph, made of lightweight nodes, that holds all the elements in a window or panel. It defines every UI you build with the UI Toolkit.
See in Glossary. It holds a reference to the root visual elementA node of a visual tree that instantiates or derives from the C# VisualElement
class. You can style the look, define the behaviour, and display it on screen as part of the UI. More info
See in Glossary of the hierarchy. For runtime UI, it’s comparable to the Canvas in UGUI.
You must attach an instance of a visual element to a panel for it to render or receive events.
Panel events fire on a visual element when its relationship with a panel changes. For example, when you add the visual element to a panel (AttachToPanelEvent
) or remove it from a panel (DetachFromPanelEvent
).
Panel events are only sent to visual elements and their descendants within a hierarchy that are directly affected when panel changes occur. Parent elements don’t receive events when descendant visual elements attach or detach from the panel.
For example, in the UXML code below, when you add the parent
visual element to a hierarchy that’s already attached to a panel, parent
, child
, and grandchild
all receive the same event. If you remove parent
from the same UXML hierarchy, all visual elements would receive DetachFromPanel
events.
<ui:UXML xmlns:ui="UnityEngine.UIElements" xmlns:uie="UnityEditor.UIElements"> <ui:VisualElement name="parent"> <ui:VisualElement name="child"> <ui:VisualElement name="grandchild" /> </ui:VisualElement> </ui:VisualElement> </ui:UXML>
The base class for all panel events is PanelChangedEventBase.
Event | Description | Trickles down | Bubbles up | Cancellable |
---|---|---|---|---|
AttachToPanelEvent | Sent right after the element (or one of its parents) is attached to a panel. | |||
DetachFromPanelEvent | Sent just before an element (or one of its parents) is detached from a panel. |
originPanel
: The originPanel
contains data specific to the DetachFromPanelEvent
. It contains the source panel that the visual element detaches from during a panel change.
destinationPanel
: The destinationPanel
contains data specific to the AttachFromPanelEvent
. It provides the panel where the visual element is now attached.
The following list provides the name, description, and target of each event in the event family.
The AttachToPanelEvent
fires after a visual element attaches to a panel. It also occurs when you add a visual element to a hierarchy that’s attached to a panel.
target
: The visual element that’s attached to a panel.
The DetachFromPanelEvent
triggers before you remove a visual element from a panel. It also occurs when you remove a visual element from a hierarchy that’s attached to a panel.
target
:The visual element that’s detaching from a panel.
The following example creates an Editor window with a button that will add additional labels to the window. Clicking the labels will remove them again.
This example implements a custom label class that prints a message to the console whenever the instance of the VisualElement is attached or detached from a panel. It highlights the behavior of the AttachToPanelEvent and DetachFromPanelEvent events and how to use the originPanel and destinationPanel properties.
To see the example in action, do the following:
using UnityEditor; using UnityEngine; using UnityEngine.UIElements; public class PanelEventsTestWindow : EditorWindow { [MenuItem("Window/UI Toolkit/Panel Events Test Window")] public static void ShowExample() { PanelEventsTestWindow wnd = GetWindow<PanelEventsTestWindow>(); wnd.titleContent = new GUIContent("Panel Events Test Window"); } public void CreateGUI() { // Set a name for the panel rootVisualElement.panel.visualTree.name = "Our Window Root Visual Element"; // Add a button which will add new instances of our custom labels to the window rootVisualElement.Add(new Button(() => rootVisualElement.Add(new CustomLabel())) { text = "Add New Label" }); } } /// <summary> /// Custom label class which prints out a console message when it is attached or detached. /// </summary> public class CustomLabel : Label { private static int m_InstanceCounter = 0; private int m_LabelNumber; public CustomLabel() : base() { m_LabelNumber = ++m_InstanceCounter; text = $"Label #{m_LabelNumber} - click me to detach"; RegisterCallback<AttachToPanelEvent>(evt => { Debug.Log($"I am label {m_LabelNumber} and I " + $"just got attached to panel '{evt.destinationPanel.visualTree.name}'"); }); RegisterCallback<DetachFromPanelEvent>(evt => { Debug.Log($"I am label {m_LabelNumber} and I " + $"just got detached from panel '{evt.originPanel.visualTree.name}'"); }); // Register a pointer down callback that removes this element from the hierarchy RegisterCallback<PointerDownEvent>(evt => this.RemoveFromHierarchy()); } }
Did you find this page useful? Please give it a rating:
Thanks for rating this page!
What kind of problem would you like to report?
Thanks for letting us know! This page has been marked for review based on your feedback.
If you have time, you can provide more information to help us fix the problem faster.
Provide more information
You've told us this page needs code samples. If you'd like to help us further, you could provide a code sample, or tell us about what kind of code sample you'd like to see:
You've told us there are code samples on this page which don't work. If you know how to fix it, or have something better we could use instead, please let us know:
You've told us there is information missing from this page. Please tell us more about what's missing:
You've told us there is incorrect information on this page. If you know what we should change to make it correct, please tell us:
You've told us this page has unclear or confusing information. Please tell us more about what you found unclear or confusing, or let us know how we could make it clearer:
You've told us there is a spelling or grammar error on this page. Please tell us what's wrong:
You've told us this page has a problem. Please tell us more about what's wrong:
Thank you for helping to make the Unity documentation better!
Your feedback has been submitted as a ticket for our documentation team to review.
We are not able to reply to every ticket submitted.
When you visit any website, it may store or retrieve information on your browser, mostly in the form of cookies. This information might be about you, your preferences or your device and is mostly used to make the site work as you expect it to. The information does not usually directly identify you, but it can give you a more personalized web experience. Because we respect your right to privacy, you can choose not to allow some types of cookies. Click on the different category headings to find out more and change our default settings. However, blocking some types of cookies may impact your experience of the site and the services we are able to offer.
More information
These cookies enable the website to provide enhanced functionality and personalisation. They may be set by us or by third party providers whose services we have added to our pages. If you do not allow these cookies then some or all of these services may not function properly.
These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. They help us to know which pages are the most and least popular and see how visitors move around the site. All information these cookies collect is aggregated and therefore anonymous. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.
These cookies may be set through our site by our advertising partners. They may be used by those companies to build a profile of your interests and show you relevant adverts on other sites. They do not store directly personal information, but are based on uniquely identifying your browser and internet device. If you do not allow these cookies, you will experience less targeted advertising. Some 3rd party video providers do not allow video views without targeting cookies. If you are experiencing difficulty viewing a video, you will need to set your cookie preferences for targeting to yes if you wish to view videos from these providers. Unity does not control this.
These cookies are necessary for the website to function and cannot be switched off in our systems. They are usually only set in response to actions made by you which amount to a request for services, such as setting your privacy preferences, logging in or filling in forms. You can set your browser to block or alert you about these cookies, but some parts of the site will not then work. These cookies do not store any personally identifiable information.