ChooseContactActivity.cs

using Android.App;
using Android.OS;
using Android.Content;
using Android.Database;
using Xamarin.Forms;

namespace contact_picker.Droid
{

    [Activity (Label = "ChooseContactActivity")]

    public class ChooseContactActivity : Activity 
    {
        public string type_number = "";
        protected override void OnCreate (Bundle savedInstanceState)
        {

            base.OnCreate (savedInstanceState);

            Intent intent = new Intent(Intent.ActionPick, Android.Provider.ContactsContract.CommonDataKinds.Phone.ContentUri);
            StartActivityForResult(intent, 1);
        }

        protected override void OnActivityResult (int requestCode, Result resultCode, Intent data)
        {
            // TODO Auto-generated method stub

            base.OnActivityResult (requestCode, resultCode, data);
            if (requestCode == 1) {
                if (resultCode == Result.Ok) {

                    Android.Net.Uri contactData = data.Data;
                    ICursor cursor = ContentResolver.Query(contactData, null, null, null, null);

                    cursor.MoveToFirst();

                    string number = cursor.GetString(cursor.GetColumnIndexOrThrow(Android.Provider.ContactsContract.CommonDataKinds.Phone.Number));

                    var twopage_renderer = new MyPage();
                    MessagingCenter.Send<MyPage, string> (twopage_renderer, "num_select", number);
                    Finish ();
                    Xamarin.Forms.Application.Current.MainPage.Navigation.PopModalAsync ();

                }
                else if (resultCode == Result.Canceled)
                {
                    Finish ();               
                }
            }
        }
    }
}