From 66020c403e3cd02ea1ebdf45a0b948005c575db5 Mon Sep 17 00:00:00 2001
From: Berry Wahlberg <40695099+BerryUIKI@users.noreply.github.com>
Date: Fri, 18 Sep 2026 09:36:02 +0800
Subject: [PATCH] Fix dark mode bug on second instance dialog and SVG preview
 default theme (#1959, #1797)

---
 OPTIONS.md                                           |  6 +++---
 .../QuickLook.Plugin.ImageViewer/Plugin.cs           |  6 ++++--
 .../Webview/WebHandler.cs                            |  6 ++++--
 QuickLook/App.xaml.cs                                | 12 ++++++++----
 QuickLook/Helpers/MessageBoxPatcher.cs               |  8 +++++++-
 5 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/OPTIONS.md b/OPTIONS.md
index a5fd6b0cb..3505ee585 100644
--- a/OPTIONS.md
+++ b/OPTIONS.md
@@ -194,10 +194,10 @@ These keys are also stored in `QuickLook.config`.
   - `<RenderSvgWeb>False</RenderSvgWeb>`
 
 ### `<LastTheme>`
-- Default: `1` (`Dark`)
+- Default: `0` (`None` / follow system)
 - Type: `Integer`
-- Description: Remember the last theme used by the ImageViewer web preview.
-  - `0` = None
+- Description: Remember the last theme used by the ImageViewer web preview. If not set or set to `0`, follows the system dark/light theme.
+  - `0` = None (Follow system theme)
   - `1` = Dark
   - `2` = Light
 - Example:
diff --git a/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Plugin.cs b/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Plugin.cs
index 0dc6ad806..71876e35e 100644
--- a/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Plugin.cs
+++ b/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Plugin.cs
@@ -1,4 +1,4 @@
-// Copyright © 2017-2026 QL-Win Contributors
+// Copyright © 2017-2026 QL-Win Contributors
 //
 // This file is part of QuickLook program.
 //
@@ -243,7 +243,9 @@ public void Prepare(string path, ContextObject context)
         else
             context.PreferredSize = new Size(800, 600);
 
-        context.Theme = (Themes)SettingHelper.Get("LastTheme", 1, "QuickLook.Plugin.ImageViewer");
+        var defaultTheme = (int)(OSThemeHelper.AppsUseDarkTheme() ? Themes.Dark : Themes.Light);
+        var theme = (Themes)SettingHelper.Get("LastTheme", defaultTheme, "QuickLook.Plugin.ImageViewer");
+        context.Theme = theme == Themes.None ? (OSThemeHelper.AppsUseDarkTheme() ? Themes.Dark : Themes.Light) : theme;
     }
 
     public void View(string path, ContextObject context)
diff --git a/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Webview/WebHandler.cs b/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Webview/WebHandler.cs
index 39edb5bbc..f3e3ec029 100644
--- a/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Webview/WebHandler.cs
+++ b/QuickLook.Plugin/QuickLook.Plugin.ImageViewer/Webview/WebHandler.cs
@@ -1,4 +1,4 @@
-// Copyright © 2017-2026 QL-Win Contributors
+// Copyright © 2017-2026 QL-Win Contributors
 //
 // This file is part of QuickLook program.
 //
@@ -91,7 +91,9 @@ public static bool TryPrepare(string path, ContextObject context, out IWebMetaPr
             else
                 context.PreferredSize = new Size(800, 600);
 
-            context.Theme = (Themes)SettingHelper.Get("LastTheme", 1, "QuickLook.Plugin.ImageViewer");
+            var defaultTheme = (int)(OSThemeHelper.AppsUseDarkTheme() ? Themes.Dark : Themes.Light);
+            var theme = (Themes)SettingHelper.Get("LastTheme", defaultTheme, "QuickLook.Plugin.ImageViewer");
+            context.Theme = theme == Themes.None ? (OSThemeHelper.AppsUseDarkTheme() ? Themes.Dark : Themes.Light) : theme;
             return true;
         }
 
diff --git a/QuickLook/App.xaml.cs b/QuickLook/App.xaml.cs
index 9184585ff..d515199be 100644
--- a/QuickLook/App.xaml.cs
+++ b/QuickLook/App.xaml.cs
@@ -228,10 +228,7 @@ protected override void OnStartup(StartupEventArgs e)
         base.OnStartup(e);
 
         // Set initial theme based on system settings
-        ThemeManager.Apply(OSThemeHelper.AppsUseDarkTheme() ? ApplicationTheme.Dark : ApplicationTheme.Light);
-
-        // Initialize MessageBox patching
-        MessageBoxPatcher.Initialize();
+        EnsureThemeAndMessageBoxPatcher();
 
         CheckUpdate();
 
@@ -307,12 +304,19 @@ private bool EnsureFirstInstance(string[] args)
         }
 
         // Second instance: duplicate
+        EnsureThemeAndMessageBoxPatcher();
         MessageBox.Show(TranslationHelper.Get("APP_SECOND_TEXT"), TranslationHelper.Get("APP_SECOND"),
             MessageBoxButton.OK, MessageBoxImage.Information);
 
         return false;
     }
 
+    private static void EnsureThemeAndMessageBoxPatcher()
+    {
+        ThemeManager.Apply(OSThemeHelper.AppsUseDarkTheme() ? ApplicationTheme.Dark : ApplicationTheme.Light);
+        MessageBoxPatcher.Initialize();
+    }
+
     private void CheckUpdate()
     {
         if (SettingHelper.Get("DisableAutoUpdateCheck", false))
diff --git a/QuickLook/Helpers/MessageBoxPatcher.cs b/QuickLook/Helpers/MessageBoxPatcher.cs
index 40a01cf7a..41426e7be 100644
--- a/QuickLook/Helpers/MessageBoxPatcher.cs
+++ b/QuickLook/Helpers/MessageBoxPatcher.cs
@@ -1,4 +1,4 @@
-// Copyright © 2024 KamilDev
+// Copyright © 2024 KamilDev
 //
 // This file is part of QuickLook program.
 //
@@ -30,12 +30,18 @@ namespace QuickLook.Helpers;
 public static class MessageBoxPatcher
 {
     private static readonly Harmony Harmony = new("com.quicklook.messagebox.patch");
+    private static bool _isInitialized;
 
     /// <summary>
     /// Initializes the MessageBox patch by applying Harmony patches to the MessageBox.Show method overloads.
     /// </summary>
     public static void Initialize()
     {
+        if (_isInitialized)
+            return;
+
+        _isInitialized = true;
+
         try
         {
             Type originalType = typeof(WindowsMessageBox);