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Nitrox.Launcher/ViewModels/Abstract/ModalViewModelBase.cs

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+using System.Linq;
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using CommunityToolkit.Mvvm.Messaging;
+using HanumanInstitute.MvvmDialogs;
+using Nitrox.Launcher.Models;
+
+namespace Nitrox.Launcher.ViewModels.Abstract;
+
+/// <summary>
+///     Base class for (popup) dialog ViewModels.
+/// </summary>
+public abstract partial class ModalViewModelBase : ObservableValidator, IModalDialogViewModel, IMessageReceiver
+{
+    [ObservableProperty] private ButtonOptions? selectedOption;
+
+    bool? IModalDialogViewModel.DialogResult => (bool)this;
+
+    protected ModalViewModelBase()
+    {
+        // Always run validation first so HasErrors is set (i.e. trigger CanExecute logic).
+        ValidateAllProperties();
+    }
+
+    public static implicit operator bool(ModalViewModelBase self)
+    {
+        return self is { HasErrors: false } and not { SelectedOption: null or ButtonOptions.No };
+    }
+
+    /// <summary>
+    ///     Closes the dialog window. By default, sets the dialog result as cancelled.
+    /// </summary>
+    /// <param name="buttonOptions">The dialog result to set before closing.</param>
+    [RelayCommand]
+    public void Close(ButtonOptions? buttonOptions = null)
+    {
+        if (buttonOptions != null)
+        {
+            SelectedOption = buttonOptions;
+        }
+        ((IClassicDesktopStyleApplicationLifetime)Application.Current?.ApplicationLifetime)?.Windows.FirstOrDefault(w => w.DataContext == this)?.CloseByUser();
+    }
+
+    public virtual void Dispose()
+    {
+        WeakReferenceMessenger.Default.UnregisterAll(this);
+    }
+}

Nitrox.Launcher/ViewModels/Abstract/RoutableViewModelBase.cs

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+using System.Threading.Tasks;
+using Nitrox.Launcher.Models.Design;
+
+namespace Nitrox.Launcher.ViewModels.Abstract;
+
+public abstract class RoutableViewModelBase : ViewModelBase
+{
+    public IRoutingScreen HostScreen { get; } = AppViewLocator.HostScreen;
+
+    /// <summary>
+    ///     Loads content that the view should show. While the returned task is running a loading indicator will be visible.
+    /// </summary>
+    internal virtual Task ViewContentLoadAsync() => Task.CompletedTask;
+
+    internal virtual Task ViewContentUnloadAsync() => Task.CompletedTask;
+}

Nitrox.Launcher/ViewModels/Abstract/ViewModelBase.cs

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+using System;
+using System.Diagnostics;
+using Avalonia.Controls;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Messaging;
+using Nitrox.Launcher.Models;
+
+namespace Nitrox.Launcher.ViewModels.Abstract;
+
+public abstract class ViewModelBase : ObservableValidator, IMessageReceiver
+{
+    protected Window MainWindow => AppViewLocator.MainWindow;
+
+    protected ViewModelBase()
+    {
+        ThrowIfViewModelCtorWasEmptyWhileNonEmptyExists();
+    }
+
+    public virtual void Dispose() => WeakReferenceMessenger.Default.UnregisterAll(this);
+
+    /// <summary>
+    ///     This will check that DI did not call the empty ViewModel constructor if dependencies for another constructor aren't met.
+    /// </summary>
+    [Conditional("DEBUG")]
+    private static void ThrowIfViewModelCtorWasEmptyWhileNonEmptyExists()
+    {
+        if (Design.IsDesignMode)
+        {
+            return;
+        }
+        foreach (StackFrame stackFrame in new StackTrace(2, false).GetFrames())
+        {
+            if (stackFrame.GetMethod() is not { IsConstructor: true } method)
+            {
+                continue;
+            }
+            if (method.DeclaringType is not { IsAbstract: false } declaringType)
+            {
+                continue;
+            }
+            if (method.GetParameters().Length > 0 || declaringType.GetConstructors().Length == 1)
+            {
+                break;
+            }
+            throw new Exception($"Empty ViewModel constructor of '{declaringType.Name}' should only be used in design mode! Check that the DI-container has all the dependencies to call a different constructor.");
+        }
+    }
+}