var button2 = UIButton.FromType (UIButtonType.RoundedRect);
button2.Frame = new RectangleF (0f, 0f, 300f, 40f);
button2.SetTitle ("Tweet!", UIControlState.Normal);
button2.TouchUpInside += (sender, e) => {
    var tvc = new TWTweetComposeViewController ();
    tvc.SetInitialText ("Here is a tweet...");
    tvc.SetCompletionHandler ((result) => {
        if (result == TWTweetComposeViewControllerResult.Cancelled) {
            Console.WriteLine ("Cancelled sending the tweet!");
        } else {
            Console.WriteLine ("Tweet sent! hurrah!");
        }
        this.DismissModalViewControllerAnimated (true);
    });
    this.PresentModalViewController (tvc, true);
};
View.AddSubview (button2);