Centralize single instancing logic back in MainWindow, fix Skip(1) error due to .Args property implementation

ILSpy/App.xaml.cs

@@ -106,13 +106,7 @@ namespace ICSharpCode.ILSpy
 
 		private static void SingleInstance_NewInstanceDetected(object? sender, NewInstanceEventArgs e)
 		{
-			var mainWindow = ICSharpCode.ILSpy.MainWindow.Instance;
-
-			var args = new CommandLineArguments(e.Args);
-			if (mainWindow.HandleCommandLineArguments(args))
-			{
-				mainWindow.HandleCommandLineArgumentsAfterShowList(args);
-			}
+			ICSharpCode.ILSpy.MainWindow.Instance.HandleSingleInstanceCommandLineArguments(e.Args);
 		}
 
 		static Assembly ResolvePluginDependencies(AssemblyLoadContext context, AssemblyName assemblyName)

ILSpy/AppEnv/SingleInstance.cs

@@ -54,9 +54,10 @@ public static class SingleInstance
 
 	private static string[] GetILSpyCommandLineArgs()
 	{
-		var cmdArgs = Environment.GetCommandLineArgs().Skip(1);
-		cmdArgs = cmdArgs.Select(CommandLineTools.FullyQualifyPath);
-		return cmdArgs.ToArray();
+		// Note: NO Skip(1) here because .Args property on SingleInstanceArguments does this for us
+		return Environment.GetCommandLineArgs().AsEnumerable()
+			.Select(CommandLineTools.FullyQualifyPath)
+			.ToArray();
 	}
 
 	/// <summary>

ILSpy/MainWindow.xaml.cs

@@ -652,7 +652,19 @@ namespace ICSharpCode.ILSpy
 
 		List<LoadedAssembly> commandLineLoadedAssemblies = new List<LoadedAssembly>();
 
-		internal bool HandleCommandLineArguments(CommandLineArguments args)
+		internal async Task HandleSingleInstanceCommandLineArguments(string[] args)
+		{
+			var cmdArgs = new CommandLineArguments(args);
+
+			await Dispatcher.InvokeAsync(() => {
+				if (HandleCommandLineArguments(cmdArgs))
+				{
+					HandleCommandLineArgumentsAfterShowList(cmdArgs);
+				}
+			});
+		}
+
+		bool HandleCommandLineArguments(CommandLineArguments args)
 		{
 			LoadAssemblies(args.AssembliesToLoad, commandLineLoadedAssemblies, focusNode: false);
 			if (args.Language != null)
@@ -664,7 +676,7 @@ namespace ICSharpCode.ILSpy
 		/// Called on startup or when passed arguments via WndProc from a second instance.
 		/// In the format case, spySettings is non-null; in the latter it is null.
 		/// </summary>
-		internal void HandleCommandLineArgumentsAfterShowList(CommandLineArguments args, ILSpySettings spySettings = null)
+		void HandleCommandLineArgumentsAfterShowList(CommandLineArguments args, ILSpySettings spySettings = null)
 		{
 			var relevantAssemblies = commandLineLoadedAssemblies.ToList();
 			commandLineLoadedAssemblies.Clear(); // clear references once we don't need them anymore