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/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)