Host Avalonia controls in Windows Forms

Avalonia controls can be hosted in Windows Forms applications. This enables a step-by-step migration of existing Windows Forms applications to Avalonia.

Overview

An exemplary Windows Forms application with Avalonia controls requires at least two projects:

1. YourApp Cross platform library where you put your Avalonia controls
2. YourApp.WinForms Your existing Windows Forms application
3. YourApp.Desktop (optional) Executable Avalonia application, required only for the Visual Studio Avalonia designer

As Windows Forms is only supported on Microsoft Windows, adding Avalonia controls to your app will not make it cross platform.

Step-by-step instructions

These instruction assume that you use Visual Studio 2022 with the Avalonia extension. You can adjust the steps and leave out the YourApp.Desktop project if you are using VS Code or Rider.

1. Create both Avalonia projects
   • In Visual Studio add a new project to your solution
   • Choose Avalonia C# Project
   • Select at least Desktop as target platforms
   • Click Create
   • You should now have a YourApp and a YourApp.Desktop project in your solution
2. Add references to your existing Windows Forms project
   • A package reference to Avalonia.Desktop
   • A package reference to Avalonia.Win32.Interoperability
   • A project reference to YourApp.csproj
3. Add the following lines in your Program.cs before you call Application.Run()

AppBuilder.Configure<App>()
    .UsePlatformDetect()
    .SetupWithoutStarting();

4. Add an WinFormsAvaloniaControlHost control from the Toolbox
5. Add the following line to your form's constructor after InitializeComponent()

winFormsAvaloniaControlHost1.Content = new MainView { DataContext = new MainViewModel() };

Now you should see Avalonia's default main view Welcome to Avalonia in your Windows Forms application.

к сведению

You cannot use ReactiveUI for your Windows Forms and Avalonia controls at the same time.

If you want to use it for Avalonia you must register ReactiveUI at the AppBuilder with .UseReactiveUI() in Program.cs. Do not include a reference to ReactiveUI.WinForms otherwise interactions will not work (see #16478).