[FIX] Fix launcher crash when selecting an already-exited process (#959)

source/Reloaded.Mod.Launcher.Lib/Models/ViewModel/Application/ReloadedAppViewModel.cs

@@ -38,8 +38,20 @@ public class ReloadedAppViewModel : ObservableObject, IDisposable
     public ReloadedAppViewModel(ApplicationViewModel applicationViewModel)
     {
         ApplicationViewModel = applicationViewModel;
-        ApplicationViewModel.SelectedProcess!.EnableRaisingEvents = true;
-        ApplicationViewModel.SelectedProcess.Exited += SelectedProcessOnExited;
+        var process = ApplicationViewModel.SelectedProcess!;
+
+        process.Exited += SelectedProcessOnExited;
+        try
+        {
+            process.EnableRaisingEvents = true;
+        }
+        catch (InvalidOperationException)
+        {
+            process.Exited -= SelectedProcessOnExited;
+            ActionWrappers.ExecuteWithApplicationDispatcherAsync(() =>
+                ApplicationViewModel.ChangeApplicationPage(ApplicationSubPage.ApplicationSummary));
+            return;
+        }
 
         /* Try establish connection. */
         if (!TryGetPort(true, out _port)) 

source/Reloaded.Mod.Launcher/Pages/BaseSubpages/ApplicationPage.xaml.cs

@@ -58,13 +58,23 @@ public void Dispose()
 
     private void ReloadedMod_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
     {
-        if (sender is not FrameworkElement { DataContext: Process process }) 
+        if (sender is not FrameworkElement { DataContext: Process process })
+            return;
+
+        if (HasExitedSafe(process))
             return;
 
         ViewModel.SelectedProcess = process;
         ViewModel.ChangeApplicationPage(ApplicationSubPage.ReloadedProcess);
     }
 
+    private static bool HasExitedSafe(Process process)
+    {
+        try { return process.HasExited; }
+        catch (InvalidOperationException) { return true; }
+        catch (System.ComponentModel.Win32Exception) { return false; }
+    }
+
     private void NonReloadedMod_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
     {
         if (sender is not FrameworkElement { DataContext: Process process }) 

source/Reloaded.Mod.Loader.Tests/Launcher/ReloadedAppViewModelTests.cs

@@ -0,0 +1,88 @@
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using Reloaded.Mod.Launcher.Lib.Models.Model.Pages;
+using Reloaded.Mod.Launcher.Lib.Models.ViewModel;
+using Reloaded.Mod.Launcher.Lib.Models.ViewModel.Application;
+using Reloaded.Mod.Launcher.Lib.Static;
+
+namespace Reloaded.Mod.Loader.Tests.Launcher;
+
+/// <summary>
+/// Regression tests for https://github.com/Reloaded-Project/Reloaded-II/issues/959
+/// (selecting a Reloaded process that has already exited crashed the launcher).
+/// </summary>
+public class ReloadedAppViewModelTests : IDisposable
+{
+    private readonly SynchronizationContext _originalContext = Actions.SynchronizationContext;
+    private readonly ImmediateSynchronizationContext _context = new();
+
+    public ReloadedAppViewModelTests() => Actions.SynchronizationContext = _context;
+
+    public void Dispose() => Actions.SynchronizationContext = _originalContext;
+
+    [Fact]
+    public void Constructor_WithExitedProcess_DoesNotThrow_AndReturnsToSummary()
+    {
+        using var exitedProcess = CreateExitedProcess();
+        var appViewModel = CreateApplicationViewModel(exitedProcess);
+
+        var exception = Record.Exception(() =>
+        {
+            var viewModel = new ReloadedAppViewModel(appViewModel);
+            GC.SuppressFinalize(viewModel);
+        });
+
+        Assert.Null(exception);
+        Assert.Equal(1, _context.PostCount);
+        Assert.Equal(ApplicationSubPage.ApplicationSummary, appViewModel.Page);
+    }
+
+    /// <summary>
+    /// Returns a <see cref="Process"/> for a process that has exited, obtained by PID
+    /// (without an owned handle), the same way the launcher's process list obtains them.
+    /// </summary>
+    private static Process CreateExitedProcess()
+    {
+        // cmd.exe blocks on redirected stdin, so it stays alive until we kill it.
+        using var owner = Process.Start(new ProcessStartInfo("cmd.exe")
+        {
+            UseShellExecute = false,
+            RedirectStandardInput = true,
+            CreateNoWindow = true
+        })!;
+
+        var stale = Process.GetProcessById(owner.Id);
+        owner.Kill();
+        owner.WaitForExit();
+        return stale;
+    }
+
+    /// <summary>
+    /// The real constructor needs configs, services and a process tracker.
+    /// <see cref="ReloadedAppViewModel"/> only uses <see cref="ApplicationViewModel.SelectedProcess"/>
+    /// and <see cref="ApplicationViewModel.ChangeApplicationPage"/> on this path, so skip it.
+    /// </summary>
+    private static ApplicationViewModel CreateApplicationViewModel(Process process)
+    {
+        var viewModel = (ApplicationViewModel)RuntimeHelpers.GetUninitializedObject(typeof(ApplicationViewModel));
+        GC.SuppressFinalize(viewModel); // Finalizer calls Dispose(), which needs constructor state.
+        viewModel.SelectedProcess = process;
+        return viewModel;
+    }
+
+    /// <summary>
+    /// Runs posted callbacks immediately and counts them, standing in for the WPF dispatcher.
+    /// </summary>
+    private sealed class ImmediateSynchronizationContext : SynchronizationContext
+    {
+        public int PostCount { get; private set; }
+
+        public override void Post(SendOrPostCallback d, object state)
+        {
+            PostCount++;
+            d(state);
+        }
+
+        public override void Send(SendOrPostCallback d, object state) => d(state);
+    }
+}