Version: Unity 6.1 Alpha (6000.1)
Language : English
Load UXML and USS C# scripts
Find visual elements with UQuery

Instantiate UXML from C# scripts

To build UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary
from a UXML file, you must first load the file into a VisualTreeAsset, and then use the Instantiate() to instantiate without a parent, which creates a new TemplateContainer, or CloneTree(parent)) to clone inside a parent.

Once the UXML is instantiated, you can retrieve specific elements from the 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
with UQuery.

The following example creates a custom Editor window and loads a UXML file as its content:

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

public class MyWindow : EditorWindow  {
    [MenuItem ("Window/My Window")]
    public static void  ShowWindow () {
        EditorWindow w = EditorWindow.GetWindow(typeof(MyWindow));

        VisualTreeAsset uiAsset = AssetDatabase.LoadAssetAtPath<VisualTreeAsset>("Assets/MyWindow.uxml");
        VisualElement ui = uiAsset.Instantiate();

        w.rootVisualElement.Add(ui);
    }
}

Additional resources

Load UXML and USS C# scripts
Find visual elements with UQuery