[Registry Preview] Using TitleBar and AppWindow (#41418)

## Summary of the Pull Request
- Using TitleBar instead of custom XAML
- Using `AppWindow` (as part of WinUIEx)

<img width="1163" height="246" alt="image"
src="https://github.com/user-attachments/assets/65a65c3a-81b7-4afb-b046-57e081709e98"
/>


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## PR Checklist

- [x] Closes: #41414
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

---------

Co-authored-by: Jay <65828559+Jay-o-Way@users.noreply.github.com>

src/modules/registrypreview/RegistryPreview/MainWindow.Events.cs

@@ -15,10 +15,10 @@ namespace RegistryPreview
         /// </summary>
         private void AppWindow_Closing(Microsoft.UI.Windowing.AppWindow sender, Microsoft.UI.Windowing.AppWindowClosingEventArgs args)
         {
-            jsonWindowPlacement.SetNamedValue("appWindow.Position.X", JsonValue.CreateNumberValue(appWindow.Position.X));
-            jsonWindowPlacement.SetNamedValue("appWindow.Position.Y", JsonValue.CreateNumberValue(appWindow.Position.Y));
-            jsonWindowPlacement.SetNamedValue("appWindow.Size.Width", JsonValue.CreateNumberValue(appWindow.Size.Width));
-            jsonWindowPlacement.SetNamedValue("appWindow.Size.Height", JsonValue.CreateNumberValue(appWindow.Size.Height));
+            jsonWindowPlacement.SetNamedValue("appWindow.Position.X", JsonValue.CreateNumberValue(AppWindow.Position.X));
+            jsonWindowPlacement.SetNamedValue("appWindow.Position.Y", JsonValue.CreateNumberValue(AppWindow.Position.Y));
+            jsonWindowPlacement.SetNamedValue("appWindow.Size.Width", JsonValue.CreateNumberValue(AppWindow.Size.Width));
+            jsonWindowPlacement.SetNamedValue("appWindow.Size.Height", JsonValue.CreateNumberValue(AppWindow.Size.Height));
         }
 
         /// <summary>

src/modules/registrypreview/RegistryPreview/RegistryPreviewXAML/MainWindow.xaml

@@ -15,38 +15,19 @@
     <Window.SystemBackdrop>
         <MicaBackdrop />
     </Window.SystemBackdrop>
-
     <Grid x:Name="MainGrid" Loaded="Grid_Loaded">
         <Grid.RowDefinitions>
             <RowDefinition Height="Auto" />
             <RowDefinition Height="*" />
         </Grid.RowDefinitions>
-        <Grid
-            x:Name="titleBar"
-            Grid.Row="0"
-            Height="32"
-            Margin="16,0"
-            ColumnSpacing="16"
-            IsHitTestVisible="True">
-            <Grid.ColumnDefinitions>
-                <!--<ColumnDefinition x:Name="LeftPaddingColumn" Width="0"/>-->
-                <ColumnDefinition x:Name="IconColumn" Width="Auto" />
-                <ColumnDefinition x:Name="TitleColumn" Width="Auto" />
-                <!--<ColumnDefinition x:Name="RightPaddingColumn" Width="0"/>-->
-            </Grid.ColumnDefinitions>
-            <Image
-                Grid.Column="0"
-                Width="16"
-                Height="16"
-                VerticalAlignment="Center"
-                Source="../Assets/RegistryPreview/RegistryPreview.ico" />
-            <TextBlock
-                x:Name="titleBarText"
-                Grid.Column="1"
-                VerticalAlignment="Center"
-                Style="{StaticResource CaptionTextBlockStyle}"
-                Text="{Binding ApplicationTitle}" />
-        </Grid>
-
+        <TitleBar x:Name="titleBar">
+            <!--  This is a workaround for https://github.com/microsoft/microsoft-ui-xaml/issues/10374, once fixed we should just be using IconSource  -->
+            <TitleBar.LeftHeader>
+                <ImageIcon
+                    Height="16"
+                    Margin="16,0,0,0"
+                    Source="/Assets/RegistryPreview/RegistryPreview.ico" />
+            </TitleBar.LeftHeader>
+        </TitleBar>
     </Grid>
-</winuiex:WindowEx>
+</winuiex:WindowEx>

src/modules/registrypreview/RegistryPreview/RegistryPreviewXAML/MainWindow.xaml.cs

@@ -6,6 +6,7 @@ using System;
 using ManagedCommon;
 using Microsoft.PowerToys.Telemetry;
 using Microsoft.UI;
+using Microsoft.UI.Windowing;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Media;
@@ -23,7 +24,6 @@ namespace RegistryPreview
         private const string APPNAME = "RegistryPreview";
 
         // private members
-        private Microsoft.UI.Windowing.AppWindow appWindow;
         private JsonObject jsonWindowPlacement;
         private string settingsFolder = string.Empty;
         private string windowPlacementFile = "app-placement.json";
@@ -38,20 +38,15 @@ namespace RegistryPreview
             settingsFolder = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData) + @"\Microsoft\PowerToys\" + APPNAME;
             OpenWindowPlacementFile(settingsFolder, windowPlacementFile);
 
-            // Update the Win32 looking window with the correct icon (and grab the appWindow handle for later)
-            IntPtr windowHandle = this.GetWindowHandle();
-            WindowId windowId = Win32Interop.GetWindowIdFromWindow(windowHandle);
-            appWindow = Microsoft.UI.Windowing.AppWindow.GetFromWindowId(windowId);
-            appWindow.SetIcon("Assets\\RegistryPreview\\RegistryPreview.ico");
-
             // TODO(stefan)
-            appWindow.Closing += AppWindow_Closing;
-            Activated += MainWindow_Activated;
+            AppWindow.Closing += AppWindow_Closing;
 
             // Extend the canvas to include the title bar so the app can support theming
             ExtendsContentIntoTitleBar = true;
+            IntPtr windowHandle = this.GetWindowHandle();
             WindowHelpers.ForceTopBorder1PixelInsetOnWindows10(windowHandle);
             SetTitleBar(titleBar);
+            AppWindow.SetIcon("Assets\\RegistryPreview\\RegistryPreview.ico");
 
             // if have settings, update the location of the window
             if (jsonWindowPlacement != null)
@@ -66,7 +61,7 @@ namespace RegistryPreview
                     // check to make sure the size values are reasonable before attempting to restore the last saved size
                     if (size.Width >= 320 && size.Height >= 240)
                     {
-                        appWindow.Resize(size);
+                        AppWindow.Resize(size);
                     }
                 }
 
@@ -80,7 +75,7 @@ namespace RegistryPreview
                     // check to make sure the move values are reasonable before attempting to restore the last saved location
                     if (point.X >= 0 && point.Y >= 0)
                     {
-                        appWindow.Move(point);
+                        AppWindow.Move(point);
                     }
                 }
             }
@@ -92,20 +87,6 @@ namespace RegistryPreview
             PowerToysTelemetry.Log.WriteEvent(new RegistryPreviewEditorStartFinishEvent() { TimeStamp = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() });
         }
 
-        private void MainWindow_Activated(object sender, WindowActivatedEventArgs args)
-        {
-            if (args.WindowActivationState == WindowActivationState.Deactivated)
-            {
-                titleBarText.Foreground =
-                    (SolidColorBrush)Application.Current.Resources["WindowCaptionForegroundDisabled"];
-            }
-            else
-            {
-                titleBarText.Foreground =
-                    (SolidColorBrush)Application.Current.Resources["WindowCaptionForeground"];
-            }
-        }
-
         private void Grid_Loaded(object sender, RoutedEventArgs e)
         {
             MainGrid.Children.Add(MainPage);
@@ -118,23 +99,23 @@ namespace RegistryPreview
 
             if (string.IsNullOrEmpty(filename))
             {
-                titleBarText.Text = APPNAME;
-                appWindow.Title = APPNAME;
+                titleBar.Title = APPNAME;
+                AppWindow.Title = APPNAME;
             }
             else
             {
                 string[] file = filename.Split('\\');
                 if (file.Length > 0)
                 {
-                    titleBarText.Text = file[file.Length - 1] + " - " + APPNAME;
+                    titleBar.Title = file[file.Length - 1] + " - " + APPNAME;
                 }
                 else
                 {
-                    titleBarText.Text = filename + " - " + APPNAME;
+                    titleBar.Title = filename + " - " + APPNAME;
                 }
 
                 // Continue to update the window's title, after updating the custom title bar
-                appWindow.Title = titleBarText.Text;
+                AppWindow.Title = titleBar.Title;
             }
         }
     }