ProjectWindowのフォルダを全部閉じるエディタ拡張

ProjectBrowserHelperWindow.cs

using System.Linq;
using System.Reflection;
using UnityEditor;
using UnityEngine;
using UnityEngine.UIElements;

public class ProjectBrowserHelperWindow : EditorWindow
{
    [MenuItem("Window/ProjectBrowserHelper")]
    static void Init()
    {
        GetWindow<ProjectBrowserHelperWindow>();
    }

    void OnEnable()
    {
        var collapseAllButton = new Button(() => OnClickCollapseAll());
        collapseAllButton.text = "Collapse All";
        rootVisualElement.Add(collapseAllButton);
    }

    void OnClickCollapseAll()
    {
        Selection.activeObject = null;
        var window =
        Resources.FindObjectsOfTypeAll<EditorWindow>().FirstOrDefault(x => x.GetType().Name == "ProjectBrowser");
        if (window == null) { return; }

        new InternalProjectBrowser(window).ClearExpandedIDs();
        window.Repaint();
    }

    /// <summary>
    /// UnityEditor.ProjectBrowserのリフレクション
    /// </summary>
    class InternalProjectBrowser
    {
        SerializedObject so;

        SerializedProperty AssetTreeExpandedIDsProperty => so.FindProperty("m_AssetTreeState.m_ExpandedIDs");
        SerializedProperty FolderTreeExpandedIDsProperty => so.FindProperty("m_FolderTreeState.m_ExpandedIDs");

        public InternalProjectBrowser(EditorWindow ProjectWindow)
        {
            so = new SerializedObject(ProjectWindow);
        }

        public void ClearExpandedIDs()
        {
            so.Update();
            AssetTreeExpandedIDsProperty.ClearArray();
            FolderTreeExpandedIDsProperty.ClearArray();
            AssetTreeExpandedIDsProperty.arraySize = 0;
            FolderTreeExpandedIDsProperty.arraySize = 0;
            so.ApplyModifiedProperties();
            Reload();
        }

        void Reload()
        {
            var methodInfo = so.targetObject.GetType().GetMethod("ResetViews", BindingFlags.Instance | BindingFlags.NonPublic);
            methodInfo.Invoke(so.targetObject, new object[0]);
        }
    }
}