Xamarin Forms page returning a result

ResultPage.cs

// http://forums.xamarin.com/discussion/comment/129611/#Comment_129611

public interface IPageWithResult<out T>
{
    T PageResult { get; }
}

public static class PageExtensions
{
    public static Task<TResult> ShowModalAsync<TPage, TResult>(this TPage page)
        where TPage : Page, IPageWithResult<TResult>
    {
        var tcs = new TaskCompletionSource<TResult>();

        System.EventHandler<ModalPoppedEventArgs> handler = null;
        handler = (_, args) =>
            {
                if (args.Modal == page)
                {
                    Application.Current.ModalPopped -= handler;
                    tcs.SetResult(page.PageResult);
                }
            };

        Application.Current.ModalPopped += handler;
        Application.Current.MainPage.Navigation.PushModalAsync(page);

        return tcs.Task;
    }
}

// Usage:

public partial class Page2 : IPageWithResult<string>

var modalPage = new Page2();
string result = await modalPage.ShowModalAsync<Page2, string>();
Debug.WriteLine(result);