Refactor: make `IPC` class public, add `SendWithArgs` method for improved inter-process communication, and streamline handling of multiple instances within startup logic.

src/PicView.Avalonia/Navigation/IPC.cs

@@ -1,5 +1,6 @@
 using System.Diagnostics;
 using System.IO.Pipes;
+using System.Runtime.InteropServices;
 using Avalonia;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Threading;
@@ -15,7 +16,7 @@ namespace PicView.Avalonia.Navigation;
 /// enabling the transfer of commands or data between them.
 /// </summary>
 // ReSharper disable once InconsistentNaming
-internal static class IPC
+public static class IPC
 {
     /// <summary>
     /// The default name for the named pipe used by the application.
@@ -24,6 +25,40 @@ internal static class IPC
     private const string PipeName = "PicViewPipe";
     
     private static bool? _isRunning;
+    
+    public static void SendWithArgs(string[] args)
+    {
+        if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+        {
+            return;
+        }
+
+        if (Settings.UIProperties.OpenInSameWindow && ProcessHelper.CheckIfAnotherInstanceIsRunning())
+        {
+            RetrySendingArgs(args);
+        }
+    }
+
+    private static void RetrySendingArgs(string[] args)
+    {
+        if (args.Length > 1)
+        {
+            Task.Run(async () =>
+            {
+                var retries = 0;
+                while (!await SendArgumentToRunningInstance(args[1]))
+                {
+                    await Task.Delay(1000);
+                    if (++retries > 20)
+                    {
+                        break;
+                    }
+                }
+
+                Environment.Exit(0);
+            });
+        }
+    }
 
     /// <summary>
     /// Sends an argument to a running instance of the application via the specified named pipe.
@@ -36,7 +71,7 @@ internal static class IPC
     /// it sends the argument. In case of a timeout or other exceptions, these errors are caught and logged in debug mode.
     /// This can be used to pass new command-line arguments to a running instance instead of starting a new instance.
     /// </remarks>
-    internal static async Task<bool> SendArgumentToRunningInstance(string arg)
+    public static async Task<bool> SendArgumentToRunningInstance(string arg)
     {
         await using var pipeClient = new NamedPipeClientStream(PipeName);
         try
@@ -75,7 +110,7 @@ internal static class IPC
     /// it reads the incoming arguments and processes them. The arguments can include file paths or commands, 
     /// and they are passed to the main view model to update the UI accordingly.
     /// </remarks>
-    internal static async Task StartListeningForArguments(MainViewModel vm)
+    public static async Task StartListeningForArguments(MainViewModel vm)
     {
         if (_isRunning.HasValue && !_isRunning.Value)
         {

src/PicView.Avalonia/SettingsManagement/SettingsUpdater.cs

@@ -292,13 +292,13 @@ public static class SettingsUpdater
     {
         if (Settings.UIProperties.OpenInSameWindow)
         {
-            _ = IPC.StartListeningForArguments(vm);
-            Settings.UIProperties.OpenInSameWindow = true;
+            IPC.StopListening();
+            Settings.UIProperties.OpenInSameWindow = false;
         }
         else
         {
-            IPC.StopListening();
-            Settings.UIProperties.OpenInSameWindow = false;
+            _ = IPC.StartListeningForArguments(vm);
+            Settings.UIProperties.OpenInSameWindow = true;
         }
 
         await SaveSettingsAsync();

src/PicView.Avalonia/StartUp/StartUpHelper.cs

@@ -55,14 +55,7 @@ public static class StartUpHelper
                 }
                 else
                 {
-                    if (!RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-                    {
-                        if (Settings.UIProperties.OpenInSameWindow &&
-                            ProcessHelper.CheckIfAnotherInstanceIsRunning())
-                        {
-                            HandleMultipleInstances(args);
-                        }
-                    }
+                    IPC.SendWithArgs(args);
                 }
             }
         }
@@ -172,7 +165,7 @@ public static class StartUpHelper
 
         if (!RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
         {
-            if (Settings.UIProperties.OpenInSameWindow && !ProcessHelper.CheckIfAnotherInstanceIsRunning())
+            if (!ProcessHelper.CheckIfAnotherInstanceIsRunning())
             {
                 // No other instance is running, create named pipe server
                 _ = IPC.StartListeningForArguments(vm);
@@ -293,27 +286,6 @@ public static class StartUpHelper
         window.WindowStartupLocation = WindowStartupLocation.CenterScreen;
     }
 
-    private static void HandleMultipleInstances(string[] args)
-    {
-        if (args.Length > 1)
-        {
-            Task.Run(async () =>
-            {
-                var retries = 0;
-                while (!await IPC.SendArgumentToRunningInstance(args[1]))
-                {
-                    await Task.Delay(1000);
-                    if (++retries > 20)
-                    {
-                        break;
-                    }
-                }
-
-                Environment.Exit(0);
-            });
-        }
-    }
-
     private static void SetWindowEventHandlers(Window w)
     {
         w.KeyDown += async (_, e) => await MainKeyboardShortcuts.MainWindow_KeysDownAsync(e).ConfigureAwait(false);