main.cs

using Android.App;
using Android.Content;
using Android.Content.PM;
using Android.OS;
using Android.Speech;
using Xamarin.Forms;

namespace XFSpeechDemo.Droid
{
    [Activity(Label = "XFSpeechDemo", Icon = "@mipmap/icon", Theme = "@style/MainTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity , IMessageSender
    {
        private readonly int VOICE = 10;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            TabLayoutResource = Resource.Layout.Tabbar;
            ToolbarResource = Resource.Layout.Toolbar;

            base.OnCreate(savedInstanceState);
            global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
            LoadApplication(new App());
        }
        protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
        {

            if (requestCode == VOICE)
            {
                if (resultCode == Result.Ok)
                {
                    var matches = data.GetStringArrayListExtra(RecognizerIntent.ExtraResults);
                    if (matches.Count != 0)
                    {
                        string textInput = matches[0];
                        MessagingCenter.Send<IMessageSender, string>(this, "STT", textInput);
                    }
                    else
                    {
                        MessagingCenter.Send<IMessageSender, string>(this, "STT", "No input");
                    }

                }
            }
            base.OnActivityResult(requestCode, resultCode, data);
        }
    }
}