Unity：UI Elements で共通コントロールを作成する

Button {
    font-size: 15px;
    -unity-font-style: bold;
    color: rgb(255, 0, 0);
}

using System;
using System.Collections.Generic;
using UnityEditor;
using UnityEngine.UIElements;


namespace MyControls
{
    internal class RedButton : VisualElement
    {
        public new class UxmlFactory : UxmlFactory<RedButton, UxmlTraits> { }

        public new class UxmlTraits : VisualElement.UxmlTraits
        {
            UxmlStringAttributeDescription m_Text =
                new UxmlStringAttributeDescription { name = "text", defaultValue = "none label" };

            public override IEnumerable<UxmlChildElementDescription> uxmlChildElementsDescription
            {
                get { yield break; }
            }

            public override void Init(VisualElement ve, IUxmlAttributes bag, CreationContext cc)
            {
                base.Init(ve, bag, cc);
                var text = m_Text.GetValueFromBag(bag, cc);
                ((RedButton)ve).Init(text);
            }
        }

        private Button m_button;

        public string text
        {
            get { return m_button.text; }
            set { m_button.text = value; }
        }

        public event Action<EventBase> clicked;

        public RedButton()
        {
            var styleSheet = AssetDatabase.LoadAssetAtPath<StyleSheet>("Assets/Editor/RedButton.uss");
            styleSheets.Add(styleSheet);

            m_button = new Button();
            m_button.text = "noen label";
            m_button.clickable.clickedWithEventInfo += Button_Clicked;
            hierarchy.Add(m_button);
        }

        public RedButton(string text) : this()
        {
            Init(text);
        }

        public void Init(string text)
        {
            this.text = text;
        }

        private void Button_Clicked(EventBase eb)
        {
            eb.target = this;
            clicked?.Invoke(eb);
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<engine:UXML
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:engine="UnityEngine.UIElements"
    xmlns:editor="UnityEditor.UIElements"
    xmlns:my="MyControls"
    xsi:noNamespaceSchemaLocation="../../UIElementsSchema/UIElements.xsd"
    xsi:schemaLocation="UnityEngine.UIElements ../../UIElementsSchema/UnityEngine.UIElements.xsd">

  <engine:Label text="Sample1 UXML" />

  <my:RedButton text="button1" name="btn1" />
  <my:RedButton text="button2" name="btn2" />
  <my:RedButton text="button3" name="btn3" />

  <engine:Label text="Sample1 UXML end" />
</engine:UXML>

Label {
    font-size: 20px;
    -unity-font-style: bold;
    color: rgb(68, 138, 255);
}

using MyControls;
using UnityEditor;
using UnityEngine;
using UnityEngine.UIElements;

public class Sample1 : EditorWindow
{
    [MenuItem("UIElementsSamples/Sample1")]
    public static void ShowExample()
    {
        Sample1 wnd = GetWindow<Sample1>();
        wnd.titleContent = new GUIContent("Sample1");
    }

    public void OnEnable()
    {
        VisualElement root = rootVisualElement;

        var visualTree = AssetDatabase.LoadAssetAtPath<VisualTreeAsset>("Assets/Editor/Sample1.uxml");
        VisualElement labelFromUXML = visualTree.CloneTree();
        root.Add(labelFromUXML);

        root.Q<RedButton>("btn1").clicked += ButtonClicked;
        root.Q<RedButton>("btn2").clicked += ButtonClicked;
        root.Q<RedButton>("btn3").clicked += ButtonClicked;
    }

    void ButtonClicked(EventBase eventBase)
    {
        var redButton = (RedButton)eventBase.target;
        Debug.Log($"Clicked {redButton.text} RedButton!! ");
    }
}