MahApps.Metro dialogs with ReactiveUI

App.xaml

<Application x:Class="ReactiveUIMahAppsDialog.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <!-- MahApps.Metro resource dictionaries. Make sure that all file names are Case Sensitive! -->
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
                <!-- Theme setting -->
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Themes/Light.Blue.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.FlatButton.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

App.xaml.cs

using System.Reflection;
using System.Windows;
using ReactiveUI;
using Splat;

namespace ReactiveUIMahAppsDialog
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        public App()
        {
            Locator.CurrentMutable.RegisterViewsForViewModels(Assembly.GetCallingAssembly());
        }
    }
}

ChildView.xaml

<reactiveUi:ReactiveUserControl
    x:Class="ReactiveUIMahAppsDialog.ChildView"
    x:TypeArguments="viewModels:ChildViewModel"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:reactiveUi="http://reactiveui.net"
    xmlns:viewModels="clr-namespace:ReactiveUIMahAppsDialog"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <Button x:Name="Test" Content="Show Dialog" Width="100" Height="100"/>
    </Grid>
</reactiveUi:ReactiveUserControl>

ChildView.xaml.cs

using System.Reactive;
using System.Reactive.Disposables;
using System.Windows;
using MahApps.Metro.Controls;
using MahApps.Metro.Controls.Dialogs;
using ReactiveUI;
using Splat;

namespace ReactiveUIMahAppsDialog
{
    public partial class ChildView
    {
        public ChildView()
        {
            InitializeComponent();

            this.WhenActivated(disposables =>
            {
                ViewModel ??= Locator.Current.GetService<ChildViewModel>() ?? new ChildViewModel();

                this.BindCommand(ViewModel,
                        viewModel => viewModel.LogInUser,
                        view => view.Test)
                    .DisposeWith(disposables);

                this.ViewModel.Message
                    .RegisterHandler(async interaction =>
                    {
                        MetroWindow window = (MetroWindow) Window.GetWindow(this);

                        await window.ShowMessageAsync("test", "test");

                        interaction.SetOutput(Unit.Default);
                    })
                    .DisposeWith(disposables);
            });
        }
    }
}

ChildViewModel.cs

using System.Reactive;
using System.Reactive.Linq;
using ReactiveUI;

namespace ReactiveUIMahAppsDialog
{
    public class ChildViewModel : ReactiveObject
    {
        public ChildViewModel()
        {
            Message = new Interaction<Unit, Unit>();

            LogInUser = ReactiveCommand.CreateFromTask(async _ => await Message.Handle(Unit.Default));
        }

        public ReactiveCommand<Unit, Unit> LogInUser { get; }

        public Interaction<Unit, Unit> Message { get; }
    }
}

MainWindow.xaml

<mah:MetroWindow
    x:Class="ReactiveUIMahAppsDialog.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:mah="http://metro.mahapps.com/winfx/xaml/controls"
    xmlns:reactiveUiMahAppsDialog="clr-namespace:ReactiveUIMahAppsDialog"
    mc:Ignorable="d"
    Title="MainWindow" Height="450" Width="800"
    WindowStartupLocation="CenterScreen">
    <Grid>
        <reactiveUiMahAppsDialog:ChildView/>
    </Grid>
</mah:MetroWindow>

MainWindow.xaml.cs

namespace ReactiveUIMahAppsDialog
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }
}

ReactiveUIMahAppsDialog.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net5.0-windows</TargetFramework>
    <UseWPF>true</UseWPF>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="MahApps.Metro" Version="2.4.5" />
    <PackageReference Include="ReactiveUI.WPF" Version="13.2.18" />
  </ItemGroup>

</Project>