Xamarin的.Android定时器更新UI - runonuthread

我正在开发Xamarin。Android应用程序，它引用了一个带有视图模型的可移植类库。正在使用MvvmCross。我需要一个计时器，每次它"滴答"时更新UI。我似乎无法让它更新UI。通过使用调试器确认，它每秒执行Tick方法。我需要使用runonuthread方法，但我不确定如何在Xamarin中实现它。一个代码示例导致tick更新UI线程将被欣赏。

Ticker.cs:

using System;
using Pong.Core.Models;
using Pong.Core.ViewModels;
using System.Threading;
namespace Pong.Droid
{
    public class Ticker
    {
        private readonly Timer _dispatcherTimer;
        private readonly GamePlayViewModel _viewModel;

        public Ticker(GamePlayViewModel viewModel)
        {
            _viewModel = viewModel;
            TimerCallback timerDelegate = new TimerCallback (Tick);
            _dispatcherTimer = new Timer (timerDelegate, null, 0, 1000);
        }

        public void Tick(object state)
        {
            _viewModel.Number++;

            //_viewModel.UpdateBall();
            //_viewModel.UpdatePaddle1();
        }
    }
}

活动:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Pong.Core.ViewModels;
using Cirrious.MvvmCross.Droid.Views;
using Android.Content.PM;
namespace Pong.Droid
{
    [Activity (Label = "GamePlayView", ScreenOrientation = ScreenOrientation.Landscape)]            
    public class GamePlayView : MvxActivity
    {
        private GamePlayViewModel _vm;
        protected override void OnCreate (Bundle bundle)
        {
            base.OnCreate (bundle);
            SetContentView (Resource.Layout.GamePlayView);
            _vm = new GamePlayViewModel();
            DataContext = _vm;
            var ticker = new Ticker(_vm);
        }
    }
}

布局:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:local="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="40dp"/>
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="40dp"
        local:MvxBind="Text Number" />
</LinearLayout>

viewmodel:

using Pong.Core.Models;
using System.Diagnostics;
using Cirrious.MvvmCross.ViewModels;

namespace Pong.Core.ViewModels
{
    public class GamePlayViewModel : MvxViewModel
    {
        protected Paddle Paddle1;
        private Paddle _paddle2; // Not yet implemented
        protected StandardBall StandardBall;
        public int Number { get; set; }
        public GamePlayViewModel()
        {
            Paddle1 = new Paddle();
            StandardBall = new StandardBall();
            Number = 1;
        }
        public void UpdatePaddle1()
        {
            switch (Paddle1.DetectWallCollision())
            {
                case "upper":
                    Paddle1.UpperWallHit();
                    break;
                case "lower":
                    Paddle1.LowerWallHit();
                    break;
                case "none":
                    Paddle1.MoveOneFrame();
                    break;
            }
        }
        public void UpdateBall()
        {
            if (StandardBall.DetectWallCollision()) StandardBall.HandleWallCollision();
            StandardBall.MoveOneFrame();
        }
        public void SetPaddleDirection(string direction)
        {
            Paddle1.SetDirection(direction);
        }
        public void StopPaddle()
        {
            Paddle1.StopMoving();
        }
    }
}

public void Tick(object state)
{            
    RunOnUiThread (() => _viewModel.Number++);
}