Easy way to asynchronously speak some text on iOS with C#

Speaker.cs

using System;
using MonoTouch.AVFoundation;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace Praeclarum
{
	/// <summary>
	/// Easy way to asynchronously speak some text.
	/// <code>
	/// await Speaker.SayAsync ("Hello");
	/// await Speaker.SayAsync ("World");
	/// </code>
	/// </summary>
	public static class Speaker
	{
		static AVSpeechSynthesizer synth = null;
//		static AVSpeechSynthesisVoice synthVoice = null;

		static readonly Dictionary<AVSpeechUtterance, UtteranceInfo> activeUtterances = new Dictionary<AVSpeechUtterance, UtteranceInfo> ();

		/// <summary>
		/// Speaks the text passed in.
		/// </summary>
		/// <returns>The speach task.</returns>
		/// <param name="text">The text to speak.</param>
		public static Task SayAsync (string text)
		{
			if (synth == null) {
				synth = new AVSpeechSynthesizer ();
				synth.DidFinishSpeechUtterance += HandleDidFinishSpeechUtterance;
			}

//			if (synthVoice == null) {
//				foreach (var v in AVSpeechSynthesisVoice.GetSpeechVoices ()) {
//					Console.WriteLine (v.Language);
//				}
//				synthVoice = AVSpeechSynthesisVoice.FromLanguage ("en-GB");
//			}

			var utt = new UtteranceInfo (text);
			activeUtterances [utt.Utterance] = utt;
			synth.SpeakUtterance (utt.Utterance);

			return utt.Completion.Task;
		}

		class UtteranceInfo
		{
			public readonly AVSpeechUtterance Utterance;
			public readonly TaskCompletionSource<object> Completion;

			public UtteranceInfo (string text)
			{
				Utterance = new AVSpeechUtterance (text) {
					Rate = 0.333f,
//					PitchMultiplier = 0.9f,
				};
				Completion = new TaskCompletionSource<object> ();
			}
		}

		static void HandleDidFinishSpeechUtterance (object sender, AVSpeechSynthesizerUteranceEventArgs e)
		{
			UtteranceInfo info;
			if (activeUtterances.TryGetValue (e.Utterance, out info)) {
				activeUtterances.Remove (e.Utterance);
				info.Completion.SetResult (null);
			}
		}
	}
}