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MessageBox

Avalonia does not include a built-in MessageBox control. This is a deliberate design choice, as Avalonia targets multiple platforms (desktop, mobile, browser) where a traditional modal message box does not always make sense. The feature is under consideration for future development.

For updates and discussion, see the MessageBox feature request on GitHub.

Adding message box functionality to your app​

Because there is no native MessageBox API, you need to use a third-party library or build your own dialog. Follow these steps to get started with a community package:

Step 1: Choose a library​

Review the options listed below and pick one that fits your project. Some are free and open-source, while others are commercial (marked with $).

Step 2: Install the NuGet package​

Install the package using the .NET CLI or your IDE's NuGet package manager. For example, to install MessageBox.Avalonia:

dotnet add package MessageBox.Avalonia

Step 3: Show a message box​

Each library has its own API. The following example uses MessageBox.Avalonia to display a simple informational dialog:

using MsBox.Avalonia;
using MsBox.Avalonia.Enums;

var box = MessageBoxManager
    .GetMessageBoxStandard("Title", "Hello from Avalonia!", ButtonEnum.Ok);

await box.ShowAsync();

If you need to capture the user's response (for example, OK vs. Cancel), store the return value:

var result = await box.ShowAsync();

if (result == ButtonResult.Ok)
{
    // Handle confirmation
}

Step 4: Handle platform differences​

Keep the following edge cases in mind:

  • Browser and mobile targets: Modal dialogs may not behave the same way as on desktop. Some libraries render the dialog inline rather than as a separate window. Test your chosen library on every platform you plan to support.
  • Single-view applications: If your app uses SingleViewApplicationLifetime (common on mobile and browser), you cannot create a new Window to host a dialog. Use a library that supports overlay or in-app dialog rendering, such as DialogHost.Avalonia.
  • Threading: Always show dialogs on the UI thread. If you are calling from a background thread, dispatch the call using Dispatcher.UIThread.InvokeAsync.

Third-party MessageBox implementations​

LibraryType
MessageBox.AvaloniaFree / Open-source
DialogHost.AvaloniaFree / Open-source
Ursa.AvaloniaFree / Open-source
AtomUI.AvaloniaFree / Open-source
Actipro Avalonia UI ControlsCommercial
Eremex Avalonia UI ControlsCommercial

Building your own message box​

If you prefer not to take a dependency on a third-party package, you can create a simple dialog window yourself:

  1. Create a new Window with the message content and buttons laid out in AXAML.
  2. Open it using window.ShowDialog(ownerWindow), which returns a Task you can await.
  3. Set the dialog result before closing by assigning a value to Window.Close(result).
<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Confirm"
        Width="300" Height="150"
        WindowStartupLocation="CenterOwner">
    <StackPanel Margin="20" Spacing="16">
        <TextBlock Text="Are you sure?" />
        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Spacing="8">
            <Button Content="Yes" Click="OnYesClick" />
            <Button Content="No" Click="OnNoClick" />
        </StackPanel>
    </StackPanel>
</Window>
public partial class ConfirmDialog : Window
{
    public ConfirmDialog()
    {
        InitializeComponent();
    }

    private void OnYesClick(object? sender, RoutedEventArgs e)
    {
        Close(true);
    }

    private void OnNoClick(object? sender, RoutedEventArgs e)
    {
        Close(false);
    }
}

To show the dialog and read the result:

var dialog = new ConfirmDialog();
var result = await dialog.ShowDialog<bool>(this);

if (result)
{
    // User clicked Yes
}

This approach only works in desktop applications that use ClassicDesktopStyleApplicationLifetime. For single-view apps, you need an overlay-based solution instead.

See also​

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