Unity：UIElements の使い方（Unity2019新機能）

<?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:upm="UnityEditor.PackageManager.UI"

xsi:noNamespaceSchemaLocation="../../UIElementsSchema/UIElements.xsd"
xsi:schemaLocation="
                        UnityEngine.UIElements ../../UIElementsSchema/UnityEngine.UIElements.xsd
                        UnityEditor.UIElements ../../UIElementsSchema/UnityEditor.UIElements.xsd
                        UnityEditor.PackageManager.UI ../../UIElementsSchema/UnityEditor.PackageManager.UI.xsd
"
>
    <engine:Label text="Hello World! From UXML" />
</engine:UXML>

Label {
    font-size: 20;
    font-weight: bold;
    text-color: rgb(68, 138, 255);
}

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


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

    public void OnEnable()
    {
        // Each editor window contains a root VisualElement object
        VisualElement root = rootVisualElement;

        // VisualElements objects can contain other VisualElement following a tree hierarchy.
        VisualElement label = new Label("Hello World! From C#");
        root.Add(label);

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

        // A stylesheet can be added to a VisualElement.
        // The style will be applied to the VisualElement and all of its children.
        var styleSheet = AssetDatabase.LoadAssetAtPath<StyleSheet>("Assets/Editor/TestWindows.uss");
        VisualElement labelWithStyle = new Label("Hello World! With Style");
        labelWithStyle.styleSheets.Add(styleSheet);
        root.Add(labelWithStyle);
    }
}

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

[CustomEditor(typeof(AAA))]
public class TestWindows : Editor
{
    public override VisualElement CreateInspectorGUI()
    {
        var root = new VisualElement();

        // VisualElements objects can contain other VisualElement following a tree hierarchy.
        VisualElement label = new Label("Hello World! From C#");
        root.Add(label);

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

        // A stylesheet can be added to a VisualElement.
        // The style will be applied to the VisualElement and all of its children.
        var styleSheet = AssetDatabase.LoadAssetAtPath<StyleSheet>("Assets/Editor/TestWindows.uss");
        VisualElement labelWithStyle = new Label("Hello World! With Style");
        labelWithStyle.styleSheets.Add(styleSheet);
        root.Add(labelWithStyle);

        return root;
    }
}