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Create a custom binding to bind USS selectors

Learn how to create a custom binding to bind USS from an example.
Read time 3 minutesLast updated 22 days ago
Version: 2023.2+
This example shows how to create a custom binding that binds USS selectors to a visual element.

Example overview

This example creates a custom binding that assigns USS class selectors to each child element of a visual element based on the order of the child elements in the hierarchy. The first element always has the left round corner edge, while the last element always has the right round corner edge.
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 Toolkit, and C# scripting. Before you start, get familiar with the following:

Create a custom binding type

Create a custom binding type that assigns USS classes based on the sibling index. The binding updates only when the sibling index changes.
  1. Create a project in Unity with any template.
  2. In the 
    Assets
    folder of your project, create a C# script named 
    AddMenuUSSClass.cs
    with the following content:
    [!code-cs]

Create the UI and the binding

Generally speaking, you create a binding that binds to an existing property of the element. For demonstration purposes, this example creates a custom binding that binds to a property that doesn't exist in the element. You must use UXML or C# to set up the binding that binds to a non-existing property. This example uses UXML to set up the binding.
  1. In the 
    Assets
    folder of your project, create a USS file named 
    CustomBinding.uss
    with the following contents:
    .menu-button {    flex-direction: row;    height: 64px;    align-items: center;     justify-content: center;}.menu-button--first {    border-top-left-radius: 15px;    border-bottom-left-radius: 15px;    border-left-width: 2px;}.menu-button--last {    border-top-right-radius: 15px;    border-bottom-right-radius: 15px;    border-right-width: 2px;}Button {    margin: 0px;    border-color: red;}
  2. In the 
    Assets
    folder of your project, create a UXML file named 
    CustomBinding.uxml
    with the following contents:
    <ui:UXML xmlns:ui="UnityEngine.UIElements" xmlns:uie="UnityEditor.UIElements" editor-extension-mode="True">    <ui:VisualElement class="menu-button">        <ui:Button text="Bloub">            <Bindings>                <AddMenuUssClass property="add-menu-button-class" />            </Bindings>        </ui:Button>        <ui:Button text="Bip">            <Bindings>                <AddMenuUssClass property="add-menu-button-class" />            </Bindings>        </ui:Button>        <ui:Button text="Boop">            <Bindings>                <AddMenuUssClass property="add-menu-button-class" />            </Bindings>        </ui:Button>    </ui:VisualElement></ui:UXML>
  3. Double-click the 
    CustomBinding.uxml
    file to open it in UI Builder.
  4. In the StyleSheet panel, select + > Add Existing USS, and then select the 
    CustomBinding.uss
    file.
  5. Save your changes.

Test the binding

To test the binding, change the order of the button elements in the UI Builder and observe the changes in the UI Builder Viewport.
  1. Double-click the 
    CustomBinding.uxml
    file to open it in UI Builder.
  2. In the Hierarchy panel, expand the root VisualElement to display the child elements, which are buttons.
  3. Drag and drop the buttons to change their order. The first button always has the left round corner edge, while the last button always has the right round corner edge.

Additional resources