add a linux fallback for the webview

Author: GabrielDuf

src/UniGetUI.Avalonia/Views/Pages/HelpPage.axaml

@@ -74,9 +74,21 @@
                      automation:AutomationProperties.AccessibilityView="Raw"/>
 
         <!-- WebView -->
-        <Border Grid.Row="2" CornerRadius="6" ClipToBounds="True">
+        <Border x:Name="WebViewBorder" Grid.Row="2" CornerRadius="6" ClipToBounds="True">
             <wv:NativeWebView x:Name="WebViewControl"/>
         </Border>
 
+        <!-- Linux fallback -->
+        <StackPanel x:Name="LinuxFallbackPanel" Grid.Row="2"
+                    HorizontalAlignment="Center" VerticalAlignment="Center"
+                    Spacing="12" IsVisible="False">
+            <TextBlock Text="{t:Translate The built-in browser is not supported on Linux yet.}"
+                       TextAlignment="Center" TextWrapping="Wrap" MaxWidth="400"/>
+            <Button HorizontalAlignment="Center" Command="{Binding OpenInBrowserCommand}">
+                <TextBlock Text="{t:Translate Open in browser}"
+                           automation:AutomationProperties.AccessibilityView="Raw"/>
+            </Button>
+        </StackPanel>
+
     </Grid>
 </UserControl>

src/UniGetUI.Avalonia/Views/Pages/HelpPage.axaml.cs

@@ -1,7 +1,6 @@
 using Avalonia.Controls;
 using Avalonia.Interactivity;
 using UniGetUI.Avalonia.ViewModels.Pages;
-using UniGetUI.Avalonia.Views.Pages;
 
 namespace UniGetUI.Avalonia.Views.Pages;
 
@@ -17,8 +16,17 @@ public HelpPage()
         DataContext = _viewModel;
         InitializeComponent();
 
-        WebViewControl.NavigationStarted += (_, _) => NavProgressBar.IsVisible = true;
-        WebViewControl.NavigationCompleted += (_, _) =>
+        if (OperatingSystem.IsLinux())
+        {
+            WebViewBorder.IsVisible = false;
+            LinuxFallbackPanel.IsVisible = true;
+            return;
+        }
+
+        WebViewControl.NavigationStarted += (_, _) =>
+            NavProgressBar.IsVisible = true;
+
+        WebViewControl.NavigationCompleted += (_, e) =>
         {
             NavProgressBar.IsVisible = false;
             _viewModel.CurrentUrl = WebViewControl.Source?.ToString() ?? HelpPageViewModel.HelpBaseUrl;

src/UniGetUI.Avalonia/Views/Pages/ReleaseNotesPage.axaml

@@ -35,9 +35,21 @@
                      automation:AutomationProperties.AccessibilityView="Raw"/>
 
         <!-- WebView -->
-        <Border Grid.Row="2" CornerRadius="6" ClipToBounds="True">
+        <Border x:Name="WebViewBorder" Grid.Row="2" CornerRadius="6" ClipToBounds="True">
             <wv:NativeWebView x:Name="WebViewControl"/>
         </Border>
 
+        <!-- Linux fallback -->
+        <StackPanel x:Name="LinuxFallbackPanel" Grid.Row="2"
+                    HorizontalAlignment="Center" VerticalAlignment="Center"
+                    Spacing="12" IsVisible="False">
+            <TextBlock Text="{t:Translate The built-in browser is not supported on Linux yet.}"
+                       TextAlignment="Center" TextWrapping="Wrap" MaxWidth="400"/>
+            <Button HorizontalAlignment="Center" Command="{Binding OpenInBrowserCommand}">
+                <TextBlock Text="{t:Translate Open in browser}"
+                           automation:AutomationProperties.AccessibilityView="Raw"/>
+            </Button>
+        </StackPanel>
+
     </Grid>
 </UserControl>

src/UniGetUI.Avalonia/Views/Pages/ReleaseNotesPage.axaml.cs

@@ -15,7 +15,16 @@ public ReleaseNotesPage()
         DataContext = _viewModel;
         InitializeComponent();
 
-        WebViewControl.NavigationStarted += (_, _) => NavProgressBar.IsVisible = true;
+        if (OperatingSystem.IsLinux())
+        {
+            WebViewBorder.IsVisible = false;
+            LinuxFallbackPanel.IsVisible = true;
+            return;
+        }
+
+        WebViewControl.NavigationStarted += (_, _) =>
+            NavProgressBar.IsVisible = true;
+
         WebViewControl.NavigationCompleted += (_, e) =>
         {
             NavProgressBar.IsVisible = false;