Version: 2022.1
Create a bindable custom control
Manage UI asset references from C# scripts

Create a custom style for a custom control

Version: 2021.2+

This example demonstrates how to use custom USS variables in a custom control.

Example overview

This example creates a custom control that reads two colors from USS and uses them to generate a texture.

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

Prerequisites

This is an advanced example for developers familiar with 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. You are recommended to have a basic understanding of the following concepts:

  • 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
  • USS

Create the custom control and custom style

Create a C# script to define the custom control and a USS file to define the custom style.

  1. Create a Unity project with any template.

  2. Create a folder named create-custom-style-custom-control to store your files.

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

    using UnityEngine;
    using UnityEngine.UIElements;
    
    namespace UIToolkitExamples
    {
        public class ExampleElementCustomStyle : VisualElement
        {
            // Factory class, required to expose this custom control to UXML
            public new class UxmlFactory : UxmlFactory<ExampleElementCustomStyle, UxmlTraits> { }
    
            // Traits class
            public new class UxmlTraits : VisualElement.UxmlTraits { }
    
            // Use CustomStyleProperty<T> to fetch custom style properties from USS
            static readonly CustomStyleProperty<Color> S_GradientFrom = new CustomStyleProperty<Color>("--gradient-from");
            static readonly CustomStyleProperty<Color> S_GradientTo = new CustomStyleProperty<Color>("--gradient-to");
    
            // Image child element and its texture
            Texture2D m_Texture2D;
            Image m_Image;
    
            public ExampleElementCustomStyle()
            {
                // Create an Image and a texture for it. Attach Image to self.
                m_Texture2D = new Texture2D(100, 100);
                m_Image = new Image();
                m_Image.image = m_Texture2D;
                Add(m_Image);
    
                RegisterCallback<CustomStyleResolvedEvent>(OnStylesResolved);
            }
    
            // When custom styles are known for this control, make a gradient from the colors.
            void OnStylesResolved(CustomStyleResolvedEvent evt)
            {
                Color from, to;
    
                if (evt.customStyle.TryGetValue(S_GradientFrom, out from)
                    && evt.customStyle.TryGetValue(S_GradientTo, out to))
                {
                    GenerateGradient(from, to);
                }
            }
    
            public void GenerateGradient(Color from, Color to)
            {
                for (int i = 0; i < m_Texture2D.width; ++i)
                {
                    Color color = Color.Lerp(from, to, i / (float)m_Texture2D.width);
                    for (int j = 0; j < m_Texture2D.height; ++j)
                    {
                        m_Texture2D.SetPixel(i, j, color);
                    }
                }
    
                m_Texture2D.Apply();
                m_Image.MarkDirtyRepaint();
            }
        }
    }
    
  4. Create a USS file named ExampleElementCustomStyle.uss and replace its contents with the following:

    ExampleElementCustomStyle {
        --gradient-from: red;
        --gradient-to: yellow;
    }
    

Use the custom control in UI Document

Create a UI Document to use the custom control and apply the custom style to the custom control.

  1. In the ExampleElementCustomStyle folder, create a UI Document named ExampleElementCustomStyle.uxml.
  2. Double-click ExampleElementCustomStyle.uxml to open it in the UI Builder.
  3. Select Library > Project > UIToolkitExamples, and drag ExampleElementCustomStyle to the Hierarchy window. A grey square appears in the Viewport window.
  4. Add the ExampleElementCustomStyle.uss file as an existing USS. This applies the custom USS variables to the square.

Additional resources

Create a bindable custom control
Manage UI asset references from C# scripts