feat(avalonia): experimental cross-platform Avalonia port

Introduce an experimental Avalonia UI implementation, infrastructure, pages, and settings flows.\n\nAlso includes:\n- single-instance forwarding and startup/dependency handling\n- auto-update gating (battery, battery-saver, metered)\n- translation key alignment and Avalonia warning cleanup\n- CI updates to validate Avalonia formatting/style/build separately

Author: mamoreau-devolutions

.github/workflows/dotnet-test.yml

@@ -5,10 +5,12 @@ on:
     paths:
       - 'global.json'
       - '**.cs'
+      - '**.axaml'
       - '**.csproj'
       - '**.props'
       - '**.targets'
       - '**.sln'
+      - '**.slnx'
       - 'src/.editorconfig'
       - '.github/workflows/dotnet-test.yml'
 
@@ -17,10 +19,12 @@ on:
     paths:
       - 'global.json'
       - '**.cs'
+      - '**.axaml'
       - '**.csproj'
       - '**.props'
       - '**.targets'
       - '**.sln'
+      - '**.slnx'
       - 'src/.editorconfig'
       - '.github/workflows/dotnet-test.yml'
 
@@ -47,7 +51,7 @@ jobs:
       uses: actions/cache@v5
       with:
         path: ${{ env.NUGET_PACKAGES }}
-        key: ${{ runner.os }}-nuget-${{ hashFiles('global.json', 'src/**/*.csproj', 'src/**/*.props', 'src/**/*.targets', 'src/**/*.sln') }}
+        key: ${{ runner.os }}-nuget-${{ hashFiles('global.json', 'src/**/*.csproj', 'src/**/*.props', 'src/**/*.targets', 'src/**/*.sln', 'src/**/*.slnx') }}
         restore-keys: |
           ${{ runner.os }}-nuget-
 
@@ -75,15 +79,25 @@ jobs:
 
     - name: Install dependencies
       working-directory: src
-      run: dotnet restore UniGetUI.sln
+      run: |
+        dotnet restore UniGetUI.sln
+        dotnet restore UniGetUI.Avalonia.slnx
 
     - name: Check whitespace formatting
       run: dotnet format whitespace src --folder --verify-no-changes --verbosity minimal
 
-    - name: Check code style formatting
+    - name: Check code style formatting (WinUI solution)
       working-directory: src
       run: dotnet format style UniGetUI.sln --no-restore --verify-no-changes --verbosity minimal
 
+    - name: Check code style formatting (Avalonia solution)
+      working-directory: src
+      run: dotnet format style UniGetUI.Avalonia.slnx --no-restore --verify-no-changes --verbosity minimal
+
+    - name: Build Avalonia solution
+      working-directory: src
+      run: dotnet build UniGetUI.Avalonia.slnx --no-restore --verbosity minimal
+
     - name: Run Tests
       working-directory: src
       env:

src/UniGetUI.Avalonia.slnx

@@ -1,8 +1,14 @@
 <Solution>
   <Configurations>
-    <Platform Name="arm64" />
     <Platform Name="x64" />
+    <Platform Name="arm64" />
   </Configurations>
+  <Folder Name="/UniGetUI.Avalonia/">
+    <Project Path="UniGetUI.Avalonia/UniGetUI.Avalonia.csproj">
+      <Platform Solution="*|x64" Project="x64" />
+      <Platform Solution="*|arm64" Project="arm64" />
+    </Project>
+  </Folder>
   <Folder Name="/UniGetUI.Core.Logger/">
     <Project Path="UniGetUI.Core.Logger/UniGetUI.Core.Logging.csproj">
       <Platform Solution="*|arm64" Project="arm64" />

src/UniGetUI.Avalonia/App.axaml

@@ -0,0 +1,8 @@
+<Application xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="UniGetUI.Avalonia.App"
+             RequestedThemeVariant="Default">
+  <Application.Styles>
+    <StyleInclude Source="avares://UniGetUI.Avalonia/Styles/AppStyles.axaml" />
+  </Application.Styles>
+</Application>

src/UniGetUI.Avalonia/App.axaml.cs

@@ -0,0 +1,52 @@
+using System.ComponentModel;
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Markup.Xaml;
+using Avalonia.Styling;
+using Avalonia.Themes.Fluent;
+using Devolutions.AvaloniaTheme.DevExpress;
+using Devolutions.AvaloniaTheme.Linux;
+using Devolutions.AvaloniaTheme.MacOS;
+
+namespace UniGetUI.Avalonia;
+
+public partial class App : Application
+{
+    public override void Initialize()
+    {
+        AvaloniaXamlLoader.Load(this);
+
+        Styles.Insert(0, CreatePlatformTheme());
+
+        Name = "UniGetUI.Avalonia";
+    }
+
+    private static Styles CreatePlatformTheme()
+    {
+        Styles styles = OperatingSystem.IsWindows()
+            ? new DevolutionsDevExpressTheme()
+            : OperatingSystem.IsMacOS()
+                ? new DevolutionsMacOsTheme()
+                : OperatingSystem.IsLinux()
+                    ? new DevolutionsLinuxYaruTheme()
+                    : new FluentTheme();
+
+        if (styles is ISupportInitialize initializable)
+        {
+            initializable.BeginInit();
+            initializable.EndInit();
+        }
+
+        return styles;
+    }
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            desktop.MainWindow = new MainWindow();
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+}

src/UniGetUI.Avalonia/Infrastructure/AsyncCommand.cs

@@ -0,0 +1,49 @@
+using System.Windows.Input;
+
+namespace UniGetUI.Avalonia.Infrastructure;
+
+internal sealed class AsyncCommand : ICommand
+{
+    private readonly Func<Task> _executeAsync;
+    private readonly Func<bool>? _canExecute;
+    private bool _isExecuting;
+
+    public AsyncCommand(Func<Task> executeAsync, Func<bool>? canExecute = null)
+    {
+        _executeAsync = executeAsync;
+        _canExecute = canExecute;
+    }
+
+    public event EventHandler? CanExecuteChanged;
+
+    public bool CanExecute(object? parameter)
+    {
+        return !_isExecuting && (_canExecute?.Invoke() ?? true);
+    }
+
+    public async void Execute(object? parameter)
+    {
+        if (!CanExecute(parameter))
+        {
+            return;
+        }
+
+        _isExecuting = true;
+        RaiseCanExecuteChanged();
+
+        try
+        {
+            await _executeAsync();
+        }
+        finally
+        {
+            _isExecuting = false;
+            RaiseCanExecuteChanged();
+        }
+    }
+
+    public void RaiseCanExecuteChanged()
+    {
+        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
+    }
+}