public sealed partial class App
{
    private IHost AppHost { get; }

    public App()
    {
        AppHost = Host
            .CreateDefaultBuilder()
            .ConfigureServices(static services =>
            {
                // Add all available interactions
                services.AddMvvmInteractions();
                
                // or add only what you need
                services.AddSingleton<IFileInteractions, FileInteractions>();
                services.AddSingleton<IMessageInteractions, MessageInteractions>();
                services.AddSingleton<IWebInteractions, WebInteractions>();
            })
            .Build();

        // Optional. Displays unhandled exceptions using MessageInteractions.Exception.
        AppHost.Services.GetRequiredService<IMessageInteractions>().CatchUnhandledExceptions(this);

        // your code
    }
}

// Open
var file = await FileInteractions.OpenFileAsync(new OpenFileArguments
{
    SuggestedFileName = "my.txt",
    Extensions = new[] { ".txt" },
    FilterName = "My txt files",
});
if (file == null)
{
    return;
}
var text = await file.ReadTextAsync().ConfigureAwait(true);

// Save (if you need to save file from previuos step)
await file.WriteTextAsync(text).ConfigureAwait(false);

// Save As
var file = await FileInteractions.SaveFileAsync(new SaveFileArguments(".txt")
{
    SuggestedFileName = "my.txt",
    FilterName = "My txt files",
});
if (file == null)
{
    return;
}
await file.WriteTextAsync(text).ConfigureAwait(false);

await MessageInteractions.ShowMessageAsync("Message");
await MessageInteractions.ShowWarningAsync("Warning");
await MessageInteractions.ShowExceptionAsync(new InvalidOperationException("Exception"));
bool question = await MessageInteractions.ShowQuestionAsync(new QuestionData("Are you sure?"));

protected override void OnLaunched(LaunchActivatedEventArgs args)
{
#if HAS_WINUI
    var window = new Window();
    MessageInteractions.Window = window;
#endif
}

await WebInteractions.OpenUrlAsync("https://www.google.com/");