反射比较多，若高频率使用，可以将反射信息缓存下来;

 public static void ShowFolderContentsOnPrejectWindow(UnityEngine.Object obj)
        {
            var intanceID = obj.GetInstanceID();
            if (!ProjectWindowUtil.IsFolder(intanceID))
                return;

            ShowFolderContents(intanceID);
        }

        /// <summary>
        /// Selects a folder in the project window and shows its content.
        /// Opens a new project window, if none is open yet.
        /// </summary>
        /// <param name="folderInstanceID">The instance of the folder asset to open.</param>
        private static void ShowFolderContents(int folderInstanceID)
        {
            // Find the internal ProjectBrowser class in the editor assembly.
            Assembly editorAssembly = typeof(Editor).Assembly;
            System.Type projectBrowserType = editorAssembly.GetType("UnityEditor.ProjectBrowser");

            // This is the internal method, which performs the desired action.
            // Should only be called if the project window is in two column mode.
            MethodInfo showFolderContents = projectBrowserType.GetMethod(
                "ShowFolderContents", BindingFlags.Instance | BindingFlags.NonPublic);

            // Find any open project browser windows.
            UnityEngine.Object[] projectBrowserInstances = Resources.FindObjectsOfTypeAll(projectBrowserType);

            if (projectBrowserInstances.Length > 0)
            {
                for (int i = 0; i < projectBrowserInstances.Length; i++)
                    ShowFolderContentsInternal(projectBrowserInstances[i], showFolderContents, folderInstanceID);
            }
            else
            {
                EditorWindow projectBrowser = OpenNewProjectBrowser(projectBrowserType);
                ShowFolderContentsInternal(projectBrowser, showFolderContents, folderInstanceID);
            }
        }

        private static void ShowFolderContentsInternal(UnityEngine.Object projectBrowser, MethodInfo showFolderContents, int folderInstanceID)
        {
            // Sadly, there is no method to check for the view mode.
            // We can use the serialized object to find the private property.
            SerializedObject serializedObject = new SerializedObject(projectBrowser);
            bool inTwoColumnMode = serializedObject.FindProperty("m_ViewMode").enumValueIndex == 1;

            if (!inTwoColumnMode)
            {
                // If the browser is not in two column mode, we must set it to show the folder contents.
                MethodInfo setTwoColumns = projectBrowser.GetType().GetMethod(
                    "SetTwoColumns", BindingFlags.Instance | BindingFlags.NonPublic);
                setTwoColumns.Invoke(projectBrowser, null);
            }

            bool revealAndFrameInFolderTree = true;
            showFolderContents.Invoke(projectBrowser, new object[] { folderInstanceID, revealAndFrameInFolderTree });
        }

        private static EditorWindow OpenNewProjectBrowser(System.Type projectBrowserType)
        {
            EditorWindow projectBrowser = EditorWindow.GetWindow(projectBrowserType);
            projectBrowser.Show();

            // Unity does some special initialization logic, which we must call,
            // before we can use the ShowFolderContents method (else we get a NullReferenceException).
            MethodInfo init = projectBrowserType.GetMethod("Init", BindingFlags.Instance | BindingFlags.Public);
            init.Invoke(projectBrowser, null);

            return projectBrowser;
        }