public override void FetchData()
        {
            m_RootItem = new TreeViewItem(0, 0, null, "Invisible Root Item");
            SetExpanded(m_RootItem, true); // ensure always visible

            Texture2D folderIcon = EditorGUIUtility.FindTexture(EditorResources.folderIconName);

            // We want three roots: Favorites, Assets, and Saved Filters
            List <TreeViewItem> visibleRoots = new List <TreeViewItem>();

            // Fetch asset folders
            int    assetsFolderInstanceID = AssetDatabase.GetMainAssetOrInProgressProxyInstanceID("Assets");
            int    depth       = 0;
            string displayName = "Assets"; //CreateDisplayName (assetsFolderInstanceID);

            AssetsTreeViewDataSource.RootTreeItem assetRootItem = new AssetsTreeViewDataSource.RootTreeItem(assetsFolderInstanceID, depth, m_RootItem, displayName);
            assetRootItem.icon = folderIcon;
            ReadAssetDatabase("Assets", assetRootItem, depth + 1);

            // Fetch packages folder
            displayName = PackageManager.Folders.GetPackagesPath();
            AssetsTreeViewDataSource.RootTreeItem packagesRootItem = new AssetsTreeViewDataSource.RootTreeItem(ProjectBrowser.kPackagesFolderInstanceId, depth, m_RootItem, displayName);
            depth++;

            packagesRootItem.icon = folderIcon;

            var packages = PackageManagerUtilityInternal.GetAllVisiblePackages(skipHiddenPackages);

            foreach (var package in packages)
            {
                var packageFolderInstanceId = AssetDatabase.GetMainAssetOrInProgressProxyInstanceID(package.assetPath);

                displayName = !string.IsNullOrEmpty(package.displayName) ? package.displayName : package.name;
                AssetsTreeViewDataSource.PackageTreeItem packageItem = new AssetsTreeViewDataSource.PackageTreeItem(packageFolderInstanceId, depth, packagesRootItem, displayName);
                packageItem.icon = folderIcon;
                packagesRootItem.AddChild(packageItem);
                ReadAssetDatabase(package.assetPath, packageItem, depth + 1);
            }

            // Fetch saved filters
            TreeViewItem savedFiltersRootItem = SavedSearchFilters.ConvertToTreeView();

            savedFiltersRootItem.parent = m_RootItem;

            // Order
            visibleRoots.Add(savedFiltersRootItem);
            visibleRoots.Add(assetRootItem);
            visibleRoots.Add(packagesRootItem);

            m_RootItem.children = visibleRoots;

            // Get global expanded state of roots
            foreach (TreeViewItem item in m_RootItem.children)
            {
                // Do not expand Packages root item
                if (item.id == ProjectBrowser.kPackagesFolderInstanceId)
                {
                    continue;
                }
                bool expanded = EditorPrefs.GetBool(kProjectBrowserString + item.displayName, true);
                SetExpanded(item, expanded);
            }

            m_NeedRefreshRows = true;
        }
        public override void FetchData()
        {
            bool firstInitialize = !isInitialized;

            m_RootItem = new TreeViewItem(0, 0, null, "Invisible Root Item");
            SetExpanded(m_RootItem, true); // ensure always visible

            // We want three roots: Favorites, Assets, and Packages
            List <TreeViewItem> visibleRoots = new List <TreeViewItem>();

            // Favorites root
            TreeViewItem savedFiltersRootItem = SavedSearchFilters.ConvertToTreeView();

            visibleRoots.Add(savedFiltersRootItem);

            // Assets root
            int    assetsFolderInstanceID = AssetDatabase.GetMainAssetOrInProgressProxyInstanceID("Assets");
            int    depth       = 0;
            string displayName = "Assets";

            AssetsTreeViewDataSource.RootTreeItem assetRootItem = new AssetsTreeViewDataSource.RootTreeItem(assetsFolderInstanceID, depth, m_RootItem, displayName);
            assetRootItem.icon = s_FolderIcon;
            visibleRoots.Add(assetRootItem);

            // Packages root
            displayName = PackageManager.Folders.GetPackagesPath();
            AssetsTreeViewDataSource.RootTreeItem packagesRootItem = new AssetsTreeViewDataSource.RootTreeItem(ProjectBrowser.kPackagesFolderInstanceId, depth, m_RootItem, displayName);
            packagesRootItem.icon = s_FolderIcon;
            visibleRoots.Add(packagesRootItem);

            m_RootItem.children = visibleRoots;

            // Set global expanded state for roots from EditorPrefs (must be before building the rows)
            if (firstInitialize)
            {
                foreach (TreeViewItem item in m_RootItem.children)
                {
                    bool expanded = EditorPrefs.GetBool(kProjectBrowserString + item.displayName, true);
                    SetExpanded(item, expanded);
                }
            }

            // Build rows
            //-----------
            m_Rows = new List <TreeViewItem>(100);

            // Favorites
            savedFiltersRootItem.parent = m_RootItem;
            m_Rows.Add(savedFiltersRootItem);
            if (IsExpanded(savedFiltersRootItem))
            {
                foreach (var f in savedFiltersRootItem.children)
                {
                    m_Rows.Add(f);
                }
            }
            else
            {
                savedFiltersRootItem.children = CreateChildListForCollapsedParent();
            }

            // Asset folders
            m_Rows.Add(assetRootItem);
            ReadAssetDatabase("Assets", assetRootItem, depth + 1, m_Rows);

            // Individual Package folders (under the Packages root item)
            m_Rows.Add(packagesRootItem);
            var packages = PackageManagerUtilityInternal.GetAllVisiblePackages(skipHiddenPackages);

            if (IsExpanded(packagesRootItem))
            {
                depth++;
                foreach (var package in packages)
                {
                    var packageFolderInstanceId = AssetDatabase.GetMainAssetOrInProgressProxyInstanceID(package.assetPath);

                    displayName = !string.IsNullOrEmpty(package.displayName) ? package.displayName : package.name;
                    AssetsTreeViewDataSource.PackageTreeItem packageItem = new AssetsTreeViewDataSource.PackageTreeItem(packageFolderInstanceId, depth, packagesRootItem, displayName);
                    packageItem.icon = s_FolderIcon;
                    packagesRootItem.AddChild(packageItem);
                    m_Rows.Add(packageItem);
                    ReadAssetDatabase(package.assetPath, packageItem, depth + 1, m_Rows);
                }
            }
            else
            {
                if (packages.Length > 0)
                {
                    packagesRootItem.children = CreateChildListForCollapsedParent();
                }
            }

            m_NeedRefreshRows = false;
        }