Create a simple transition with UI Builder and C# scripts

Version: 2021.3+

This example demonstrates how to create simple transitions that are triggered by pseudo-classes and C# events.

Example overview

The example creates a custom Editor window with three labels that rotate and scale when you hover over them. The transition lasts for three seconds.

You can find the completed files that this example creates in this GitHub repository.

Prerequisites

This guide is for developers familiar with the Unity Editor, UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary Toolkit, and C# scripting. Before you start, get familiar with the following:

• UI Builder
• USS
• Pseudo-classes
• Handle events

Create the Editor window files

Use the menu to create the Editor window files with three default labels.

1. Create a Unity project with any template.

2. Create a folder named create-a-transition to store the files for this example.

3. In that folder, right-click in the Project window and select Create > UI Toolkit > Editor Window.

4. In the C# box, enter TransitionExample. This creates the following files:

   • TransitionExample.cs
   • TransitionExample.uss
   • TransitionExample.uxml

Create the transition with UI Builder

In UI Builder, use the StyleSheets window to create a hover style for the label, which triggers the transition. Set the transition on the label rather than the hover. If you set the transition on the hover, the transition doesn’t work if the cursor leaves the label.

1. Open TransitionExample.uxml in the UI Builder.

2. In the StyleSheets window, click Add new selector and enter Label:hover to add a hover style for the label.

3. Press Enter and select Label:hover in the list of USS selectors.

4. In the Transform section of the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
   See in Glossary, do the following to scale and rotate the labels:
   • In the Scale row, change the X value to 1.1.
   • In the Rotate row, enter 10.

5. In the StyleSheets window, click Add new selector and enter Label to add a style for the label.

6. Press Enter and select Label in the list of USS selectors.

7. In the Transition Animations section, enter 3 in the Duration row.

8. Save and close the UI Builder. Your TransitionExample.uss file looks like the following:

   .custom-label {
       font-size: 20px;
       -unity-font-style: bold;
       color: rgb(68, 138, 255);
   }
       
   Label:hover {
       scale: 1.1 1;
       rotate: 10deg;
   }
       
   Label {
       transition-duration: 3s;
   }
   

9. In Unity, select Window > UI Toolkit > Transition Example.

10. Hover over the second and third labels. The labels rotate and increase in size over three seconds.

Create the transition with C# scripts

In C#, create the same transition you did in the previous section for the first label. Use the pointer events to trigger the transition.

1. Open TransitionExample.cs in a text editor.

2. Replace the contents of TransitionExample.cs with the following:

   using UnityEditor;
   using UnityEngine;
   using UnityEngine.UIElements;
   using System.Collections.Generic;
   
   public class TransitionExample : EditorWindow
   {
       [SerializeField]
       VisualTreeAsset m_VisualTreeAsset;
   
       [MenuItem("Window/UI Toolkit/TransitionExample")]
       public static void ShowExample()
       {
           TransitionExample wnd = GetWindow<TransitionExample>();
           wnd.titleContent = new GUIContent("Transition Example");
       }
   
       public void CreateGUI()
       {
           // Each editor window contains a root VisualElement object.
           VisualElement root = rootVisualElement;
   
           // VisualElements objects can contain other VisualElement following a tree hierarchy.
           cSharpLabel = new Label("Hello World! From C#");
           root.Add(cSharpLabel);
   
           // Create transition on the new Label.
           cSharpLabel.style.transitionDuration = new List<TimeValue>{ new TimeValue(3) };
   
           // Record default rotate and scale values.
           defaultRotate = cSharpLabel.resolvedStyle.rotate;
           defaultScale = cSharpLabel.resolvedStyle.scale;
   
           // Set up event handlers to simulate the use of the :hover pseudo-class.
           cSharpLabel.RegisterCallback<PointerOverEvent>(OnPointerOver);
           cSharpLabel.RegisterCallback<PointerOutEvent>(OnPointerOut);
   
           // Instantiate UXML
           VisualElement labelFromUXML = m_VisualTreeAsset.Instantiate();
           root.Add(labelFromUXML);
       }
   
       // The Label created with C#.
       VisualElement cSharpLabel;
   
       // The default rotate and scale values for the new Label.
       Rotate defaultRotate;
       Scale defaultScale;
   
       void OnPointerOver(PointerOverEvent evt)
       {
           SetHover(evt.currentTarget as VisualElement, true);
       }
   
       void OnPointerOut(PointerOutEvent evt)
       {
           SetHover(evt.currentTarget as VisualElement, false);
       }
   
       // When the user enters or exits the Label, set the rotate and scale.
       void SetHover(VisualElement label, bool hover)
       {
           label.style.rotate = hover ? new(Angle.Degrees(10)) : defaultRotate;
           label.style.scale = hover ? new Vector2(1.1f, 1) : defaultScale;
       }
   
       // Unregister all event callbacks.
       void OnDisable()
       {
           cSharpLabel.UnregisterCallback<PointerOverEvent>(OnPointerOver);
           cSharpLabel.UnregisterCallback<PointerOutEvent>(OnPointerOut);
       }
   }
   

3. In Unity, select Window > UI Toolkit > Transition Example.

4. Hover over the first label. The label rotates and increases in size over three seconds.

Additional resources

• USS transition