VisualElementComponentAttribute

Description

Declares a struct as a UI Toolkit component: a reusable piece of data and behavior that you can attach to any VisualElement.

Components extend elements through composition instead of inheritance. Rather than writing a custom element subclass, declare a partial struct with this attribute and attach an instance to any element with VisualElement.AddComponent. The same component type works on any element, whatever its type.

This attribute targets structs. The struct must be declared partial: Unity's source generator completes it, implementing IVisualElementComponent and generating the registration code for you.

An element holds at most one component of each type. Read or modify an attached component with VisualElement.GetComponent; remove it with VisualElement.RemoveComponent.

The following example attaches a click counter to a button without subclassing it.

 using UnityEngine;
 using UnityEngine.UIElements;

 [VisualElementComponent]
 public partial struct ClickCounter
 {
     public int count;
 }

 public static class ClickCounterExample
 {
     public static void Attach(Button button)
     {
         // Attach the component with its starting value.
         button.AddComponent(new ClickCounter { count = 0 });

         button.RegisterCallback<ClickEvent>(evt =>
         {
             // GetComponent returns a reference: the increment is stored on the element.
             ref var counter = ref button.GetComponent<ClickCounter>();
             counter.count++;
             Debug.Log($"Clicked {counter.count} times.");
         });
     }
 }

Properties

Constructors