Create a bindable custom control

Version: 2021.3+

This example demonstrates how to create a bindable custom control in a custom Editor window.

Example overview

This example creates a custom control bound to a property with the double data type. You can adapt this example to bind to properties with other data types such as a string or an integer.

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
• 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
• UXML
• SerializedObject data binding

Create the custom control class

Create a C# class to define the custom control.

1. Create a Unity project with any template.

2. Create a folder named ExampleField to store your files.

3. In the ExampleField folder, create a C# script named ExampleField.cs and replace its content with the following:

   using UnityEngine.UIElements;
   
   namespace UIToolkitExamples
   {
       // ExampleField inherits from BaseField with the double type. Therefoe, the ExampleField's underlying value is a double.
       public class ExampleField : BaseField<double>
       {
           // We can provide the existing BaseFieldTraits class as a type parameter for UxmlFactory, and this means we
           // don't need to define our own traits class or override its Init() method. We do, however, need to provide it
           // However, you must provide the value type (double) and its attribute description type:
           // (UxmlDoubleAttributeDescription).
           public new class UxmlFactory :
               UxmlFactory<ExampleField, BaseFieldTraits<double, UxmlDoubleAttributeDescription>> { }
   
           Label m_Input;
   
           // Default constructor is required for compatibility with UXML factory
           public ExampleField() : this(null)
           {
   
           }
   
           // Main constructor accepts label parameter to mimic BaseField constructor.
           // Second argument to base constructor is the input element, the one that displays the value this field is
           // bound to.
           public ExampleField(string label) : base(label, new Label() { })
           {
               // This is the input element instantiated for the base constructor.
               m_Input = this.Q<Label>(className: inputUssClassName);
           }
   
           // SetValueWithoutNotify needs to be overridden by calling the base version and then making a change to the
           // underlying value be reflected in the input element.
           public override void SetValueWithoutNotify(double newValue)
           {
               base.SetValueWithoutNotify(newValue);
   
               m_Input.text = value.ToString("N");
           }
       }
   }
   

Use the custom control in a UXML file

1. In the ExampleField folder, create a UI Document named ExampleField.uxml.

2. Open ExampleField.uxml in a text editor and replace its contents with the following:

   <ui:UXML xmlns:ui="UnityEngine.UIElements" xmlns:example="UIToolkitExamples">
       <example:ExampleField label="Binding Target" binding-path="m_Value" />
   </ui:UXML>
   

3. In Unity, double-click ExampleField.uxml to open it in the UI Builder. The ExampleField displays in the Hierarchy window and is visualized in the ViewportThe user’s visible area of an app on their screen.
   See in Glossary. If you select the ExampleField in the Hierarchy window, 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 window shows the values assigned to the Binding Path and Label boxes.

Create the class and custom Editor for the binding target

1. In the ExampleField folder, create a C# script named ExampleFieldComponent.cs and replace its contents with the following:

   using UnityEngine;
   
   namespace UIToolkitExamples
   {
       public class ExampleFieldComponent : MonoBehaviour
       {
           [SerializeField]
           double m_Value;
       }
   }
   

2. In the ExampleField folder, create a folder named Editor.

3. In the Editor folder, create a C# script named ExampleFieldCustomEditor.cs and replace its contents with the following:

   using UnityEditor;
   using UnityEngine.UIElements;
   using UnityEngine;
   
   namespace UIToolkitExamples
   {
       [CustomEditor(typeof(ExampleFieldComponent))]
       public class ExampleFieldCustomEditor : Editor
       {
           [SerializeField]
           VisualTreeAsset m_Uxml;
   
           public override VisualElement CreateInspectorGUI()
           {
               var parent = new VisualElement();
   
               m_Uxml?.CloneTree(parent);
   
               return parent;
           }
       }
   }
   

4. In Unity, select ExampleFieldCustomEditor.cs in the Project windowA window that shows the contents of your Assets folder (Project tab) More info
   See in Glossary.

5. Drag ExampleField.uxml into the Uxml box in the Inspector window.

Test the example

1. In Unity, add an empty 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 to a sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
   See in Glossary.
2. Add the ExampleFieldComponent component to the GameObject. The custom control appears in the Inspector with the default value of 0 for the Binding Target. If you change the value of the underlying double property, the UI reflects that change.

Additional resources

• Custom controls