Automatically fix Office preview handler registry

This function requires QuickLook to run with administrator privileges and preview the corresponding Office file once

QuickLook.Plugin/QuickLook.Plugin.OfficeViewer/CLSIDRegister.cs

@@ -23,8 +23,10 @@ namespace QuickLook.Plugin.OfficeViewer;
 
 internal static class CLSIDRegister
 {
-    public const string Office = "{84F66100-FF7C-4fb4-B0C0-02CD7FB668FE}";
-    public const string Visio = "{279D6C9A-652E-4833-BEFC-312CA8887857}";
+    public const string MicrosoftWord = "{84F66100-FF7C-4fb4-B0C0-02CD7FB668FE}";
+    public const string MicrosoftExcel = "{00020827-0000-0000-C000-000000000046}";
+    public const string MicrosoftPowerPoint = "{65235197-874B-4A07-BDC5-E65EA825B718}";
+    public const string MicrosoftVisio = "{21E17C2F-AD3A-4b89-841F-09CFE02D16B7}";
 
     public static string GetName(string clsid)
     {

QuickLook.Plugin/QuickLook.Plugin.OfficeViewer/Plugin.cs

@@ -31,8 +31,8 @@ public class Plugin : IViewer
     [
         ".doc", ".docx", ".docm",
         ".xls", ".xlsx", ".xlsm", ".xlsb",
-        ".vsd", ".vsdx",
         ".ppt", ".pptx",
+        ".vsd", ".vsdx",
         ".odt", ".ods", ".odp"
     ];
 
@@ -52,12 +52,41 @@ public class Plugin : IViewer
         if (!Extensions.Any(path.ToLower().EndsWith))
             return false;
 
-        var previewHandler = PreviewHandlerHost.GetPreviewHandlerGUID(path);
+        var previewHandler = ShellExRegister.GetPreviewHandlerGUID(Path.GetExtension(path));
         if (previewHandler == Guid.Empty)
             return false;
 
-        if (!string.IsNullOrWhiteSpace(CLSIDRegister.GetName($"{{{previewHandler}}}")))
+        if (!string.IsNullOrWhiteSpace(CLSIDRegister.GetName(previewHandler.ToString("B"))))
+        {
             return true;
+        }
+        else
+        {
+            // To restore the preview handler CLSID to MS Office
+            // if running with administrative privileges
+            if (ShellExRegister.IsRunAsAdmin())
+            {
+                var fileExtension = Path.GetExtension(path);
+                var fallbackHandler = fileExtension switch
+                {
+                    ".doc" or ".docx" or ".docm" or ".odt" => CLSIDRegister.MicrosoftWord,
+                    ".xls" or ".xlsx" or ".xlsm" or ".xlsb" or ".ods" => CLSIDRegister.MicrosoftExcel,
+                    ".ppt" or ".pptx" or ".odp" => CLSIDRegister.MicrosoftPowerPoint,
+                    ".vsd" or ".vsdx" => CLSIDRegister.MicrosoftVisio,
+                    _ => null,
+                };
+
+                if (fallbackHandler == null)
+                    return false;
+
+                if (!string.IsNullOrWhiteSpace(CLSIDRegister.GetName(fallbackHandler)))
+                {
+                    // Admin requested
+                    ShellExRegister.SetPreviewHandlerGUID(fileExtension, new Guid(fallbackHandler));
+                    return true;
+                }
+            }
+        }
 
         return false;
     }

QuickLook.Plugin/QuickLook.Plugin.OfficeViewer/PreviewHandlerHost.cs

@@ -21,7 +21,6 @@ using System.Drawing;
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Windows.Forms;
-using Microsoft.Win32;
 
 namespace QuickLook.Plugin.OfficeViewer;
 
@@ -70,34 +69,6 @@ public class PreviewHandlerHost : Control
         base.Dispose(disposing);
     }
 
-    /// <summary>
-    /// Returns the GUID of the preview handler associated with the specified file.
-    /// </summary>
-    /// <param name="filename"></param>
-    /// <returns></returns>
-    public static Guid GetPreviewHandlerGUID(string filename)
-    {
-        // open the registry key corresponding to the file extension
-        var ext = Registry.ClassesRoot.OpenSubKey(Path.GetExtension(filename));
-        if (ext != null)
-        {
-            // open the key that indicates the GUID of the preview handler type
-            var test = ext.OpenSubKey(@"shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}");
-            if (test != null) return new Guid(Convert.ToString(test.GetValue(null)));
-
-            // sometimes preview handlers are declared on key for the class
-            var className = Convert.ToString(ext.GetValue(null));
-            if (className != null)
-            {
-                test = Registry.ClassesRoot.OpenSubKey(
-                    className + @"\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}");
-                if (test != null) return new Guid(Convert.ToString(test.GetValue(null)));
-            }
-        }
-
-        return Guid.Empty;
-    }
-
     /// <summary>
     /// Resizes the hosted preview handler when this PreviewHandlerHost is resized.
     /// </summary>
@@ -123,7 +94,7 @@ public class PreviewHandlerHost : Control
             return false;
 
         // try to get GUID for the preview handler
-        var guid = GetPreviewHandlerGUID(path);
+        var guid = ShellExRegister.GetPreviewHandlerGUID(Path.GetExtension(path));
 
         if (guid == Guid.Empty)
             return false;

QuickLook.Plugin/QuickLook.Plugin.OfficeViewer/ShellExRegister.cs

@@ -0,0 +1,66 @@
+using Microsoft.Win32;
+using System;
+using System.IO;
+using System.Security.Principal;
+
+namespace QuickLook.Plugin.OfficeViewer;
+
+internal static class ShellExRegister
+{
+    /// <summary>
+    /// Returns the GUID of the preview handler associated with the specified file extension.
+    /// </summary>
+    /// <param name="filename"></param>
+    /// <returns></returns>
+    public static Guid GetPreviewHandlerGUID(string fileExtension)
+    {
+        // open the registry key corresponding to the file extension
+        var ext = Registry.ClassesRoot.OpenSubKey(fileExtension);
+        if (ext != null)
+        {
+            // open the key that indicates the GUID of the preview handler type
+            // Such as `Computer\HKEY_CLASSES_ROOT\.docx\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}`
+            // Such as `Computer\HKEY_CLASSES_ROOT\.xlsx\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}`
+            var test = ext.OpenSubKey(@"shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}");
+            if (test != null) return new Guid(Convert.ToString(test.GetValue(null)));
+
+            // sometimes preview handlers are declared on key for the class
+            var className = Convert.ToString(ext.GetValue(null));
+            if (className != null)
+            {
+                // Such as `Computer\HKEY_CLASSES_ROOT\{CLASS_NAME}\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}`
+                test = Registry.ClassesRoot.OpenSubKey(
+                    className + @"\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}");
+                if (test != null) return new Guid(Convert.ToString(test.GetValue(null)));
+            }
+        }
+
+        return Guid.Empty;
+    }
+
+    /// <summary>
+    /// Set the GUID of the preview handler associated with the specified file extension.
+    /// </summary>
+    /// <param name="fileExtension"></param>
+    /// <param name="guid"></param>
+    public static void SetPreviewHandlerGUID(string fileExtension, Guid guid)
+    {
+        // open the registry key corresponding to the file extension
+        var ext = Registry.ClassesRoot.OpenSubKey(fileExtension);
+        if (ext != null)
+        {
+            // open the key that indicates the GUID of the preview handler type
+            // Such as `Computer\HKEY_CLASSES_ROOT\.docx\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}`
+            // Such as `Computer\HKEY_CLASSES_ROOT\.xlsx\shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}`
+            var test = ext.OpenSubKey(@"shellex\{8895b1c6-b41f-4c1c-a562-0d564250836f}", true);
+            test?.SetValue(null, guid.ToString("B"));
+        }
+    }
+
+    public static bool IsRunAsAdmin()
+    {
+        using WindowsIdentity identity = WindowsIdentity.GetCurrent();
+        WindowsPrincipal principal = new(identity);
+        return principal.IsInRole(WindowsBuiltInRole.Administrator);
+    }
+}