Sample improves

* No remove axaml files for makes the sample simpler.
* Creation of utilities class.
* Avoid using ref Bitmap on MainViewModel.
* Avoid application crashing when dotnet.png or avalonia.png are missing. Using an replace embeded image instead.
* Conditionally invoke of UseAvaloniaNative at runtime.

src/App.axaml.cs

@@ -1,3 +1,4 @@
+
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
@@ -30,12 +31,7 @@ namespace AvaloniaCoreRTDemo
             this.InitializeThemes();
             if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
             {
-                desktop.MainWindow = 
-#if !OSX
-                new MainWindow();
-#else
-                new MainWindowMacOS();
-#endif
+                desktop.MainWindow = !Utilities.IsOSX ? new MainWindow() : new MainWindowMacOS();
                 this.DataContext = desktop.MainWindow.DataContext;
             }
             base.OnFrameworkInitializationCompleted();

src/AvaloniaCoreRTDemo.csproj

@@ -99,15 +99,11 @@
     <Compile Update="Windows/MainWindow.axaml.cs">
       <DependentUpon>MainWindow.axaml</DependentUpon>
 	</Compile>
-    <AvaloniaXaml Remove="Windows/MainWindowMacOS.axaml" />
-    <Compile Remove="Windows/MainWindowMacOS.axaml.cs" />
   </ItemGroup>
   <!--OSX only xaml-->
   <ItemGroup Condition="'$(IsOSX)'=='true'">
     <Compile Update="Windows/MainWindowMacOS.axaml.cs">
       <DependentUpon>MainWindowMacOS.axaml</DependentUpon>
     </Compile>
-    <AvaloniaXaml Remove="Windows/MainWindow.axaml" />
-    <Compile Remove="Windows/MainWindow.axaml.cs" />
   </ItemGroup>
 </Project>

src/Controls/ViewModels/MainViewModel.cs

@@ -1,6 +1,5 @@
 using System;
 using System.IO;
-using System.Runtime.CompilerServices;
 
 using Avalonia.Media.Imaging;
 
@@ -13,22 +12,23 @@ namespace AvaloniaCoreRTDemo.Controls.ViewModels
         private readonly IBitmap _dotNetImage;
         private readonly IBitmap _avaloniaImage;
 
-        public IBitmap DotNetImage
-        {
-            get { return _dotNetImage; }
-            set { this.RaiseAndSetIfChanged(ref Unsafe.AsRef(this._dotNetImage), value); }
-        }
+        public IBitmap DotNetImage => this._dotNetImage;
 
-        public IBitmap AvaloniaImage
-        {
-            get { return _avaloniaImage; }
-            set { this.RaiseAndSetIfChanged(ref Unsafe.AsRef(this._avaloniaImage), value); }
-        }
+        public IBitmap AvaloniaImage => this._avaloniaImage;
 
         public MainViewModel()
         {
-            this._dotNetImage = new Bitmap(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "dotnet.png"));
-            this._avaloniaImage = new Bitmap(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "avalonia.png"));
+            this._dotNetImage = Utilities.GetImageFromFile(GetImageFullPath("dotnet.png"));
+            this._avaloniaImage = Utilities.GetImageFromFile(GetImageFullPath("avalonia.png"));
+        }
+
+        private static String GetImageFullPath(String fileName)
+            => Path.Combine(AppDomain.CurrentDomain.BaseDirectory, fileName);
+
+        ~MainViewModel()
+        {
+            this._dotNetImage.Dispose();
+            this._avaloniaImage.Dispose();
         }
     }
 }

src/Program.cs

@@ -1,9 +1,8 @@
-
-using Avalonia;
+using Avalonia;
 
 namespace AvaloniaCoreRTDemo
 {
-    class Program
+    public static class Program
     {
         // Initialization code. Don't use any Avalonia, third-party APIs or any
         // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
@@ -13,9 +12,10 @@ namespace AvaloniaCoreRTDemo
         // Avalonia configuration, don't remove; also used by visual designer.
         public static AppBuilder BuildAvaloniaApp()
             => AppBuilder.Configure<App>().UsePlatformDetect()
-#if OSX
-            .UseAvaloniaNative()
-#endif
+            .UseAvaloniaNativeOSX()
             .LogToTrace();
+
+        private static AppBuilder UseAvaloniaNativeOSX(this AppBuilder appBuilder)
+            => Utilities.IsOSX ? appBuilder.UseAvaloniaNative() : appBuilder;
     }
 }

src/Utilities.cs

@@ -0,0 +1,39 @@
+using System;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+using Avalonia.Media.Imaging;
+
+namespace AvaloniaCoreRTDemo
+{
+    internal static class Utilities
+    {
+        public static readonly Boolean IsWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+        public static readonly Boolean IsOSX = RuntimeInformation.IsOSPlatform(OSPlatform.OSX);
+
+        public static Bitmap GetImageFromResources(String fileName)
+        {
+            Assembly asm = Assembly.GetExecutingAssembly();
+            String resourceName = asm.GetManifestResourceNames().FirstOrDefault(str => str.EndsWith(fileName));
+            if (resourceName != null)
+                using (Stream bitmapStream = asm.GetManifestResourceStream(resourceName))
+                    return new Bitmap(bitmapStream);
+            else
+                return default;
+        }
+
+        public static Bitmap GetImageFromFile(String path)
+        {
+            try
+            {
+                return new Bitmap(path);
+            }
+            catch (Exception)
+            {
+                return GetImageFromResources("broken-link.png");
+            }
+        }
+    }
+}

src/Windows/ViewModels/AboutViewModel.cs

@@ -1,7 +1,4 @@
 using System;
-using System.IO;
-using System.Linq;
-using System.Reflection;
 using System.Runtime.InteropServices;
 
 using Avalonia.Media.Imaging;
@@ -34,35 +31,24 @@ namespace AvaloniaCoreRTDemo.Windows.ViewModels
         {
             get
             {
-                if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-                    return !_darkTheme ? "windows.png" : "windows_d.png";
-                else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-                    return !_darkTheme ? "macos.png" : "macos_d.png";
+                if (Utilities.IsWindows)
+                    return !this._darkTheme ? "windows.png" : "windows_d.png";
+                else if (Utilities.IsOSX)
+                    return !this._darkTheme ? "macos.png" : "macos_d.png";
                 else
-                    return !_darkTheme ? "linux.png" : "linux_d.png";
+                    return !this._darkTheme ? "linux.png" : "linux_d.png";
             }
         }
 
         public AboutViewModel(Boolean darkTheme)
         {
             this._darkTheme = darkTheme;
-            this._computerImage = GetImageFromResources(this.ComputerImageName);
+            this._computerImage = Utilities.GetImageFromResources(this.ComputerImageName);
         }
 
         ~AboutViewModel()
         {
             this._computerImage.Dispose();
         }
-
-        private static Bitmap GetImageFromResources(String fileName)
-        {
-            Assembly asm = Assembly.GetExecutingAssembly();
-            String resourceName = asm.GetManifestResourceNames().FirstOrDefault(str => str.EndsWith(fileName));
-            if (resourceName != null)
-                using (Stream bitmapStream = asm.GetManifestResourceStream(resourceName))
-                    return new Bitmap(bitmapStream);
-            else
-                return default;
-        }
     }
 }

src/Windows/ViewModels/MainViewModel.cs

@@ -55,7 +55,7 @@ namespace AvaloniaCoreRTDemo.Windows.ViewModels
         public void DefaultDarkMethod() => this.ChangeTheme(ApplicationTheme.DefaultDark);
         public void FluentLightMethod() => this.ChangeTheme(ApplicationTheme.FluentLight);
         public void FluentDarkMethod() => this.ChangeTheme(ApplicationTheme.FluentDark);
-        public void HelpAboutMethod() => base.RunHelpAbout(this._window);
+        public override void HelpAboutMethod() => base.RunHelpAbout(this._window);
 
         private void RunFileExit()
             => Environment.Exit(0);

src/Windows/ViewModels/MainViewModelBase.cs

@@ -1,8 +1,4 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 using Avalonia.Controls;
 
@@ -26,6 +22,8 @@ namespace AvaloniaCoreRTDemo.Windows.ViewModels
         public MainViewModelBase(IThemeSwitch window)
             => this._themeSwitch = window;
 
+        public abstract void HelpAboutMethod();
+
         protected async void RunHelpAbout(Window currentWindow)
         {
             if (this.AboutEnabled)