Setting up source code for Avalonia port.

src/AdvancedCalculator/App.axaml.cs

@@ -0,0 +1,41 @@
+using AdvancedCalculator.ViewModels;
+using AdvancedCalculator.Views;
+
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Data.Core.Plugins;
+using Avalonia.Markup.Xaml;
+
+namespace AdvancedCalculator;
+
+public partial class App : Application
+{
+    public override void Initialize()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        // Line below is needed to remove Avalonia data validation.
+        // Without this line you will get duplicate validations from both Avalonia and CT
+        BindingPlugins.DataValidators.RemoveAt(0);
+
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            desktop.MainWindow = new MainWindow
+            {
+                DataContext = new MainViewModel()
+            };
+        }
+        else if (ApplicationLifetime is ISingleViewApplicationLifetime singleViewPlatform)
+        {
+            singleViewPlatform.MainView = new MainView
+            {
+                DataContext = new MainViewModel()
+            };
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+}