Xamarin带有Timer的Android UI没有对变化做出反应

Question

我正在使用Xamarin Studio，我建的应用程序应该轮流切换左侧和右侧列（如警灯）。要做到这一点，我已经使用了计时器和断点，我可以看到代码运行ColorFlip和值正在设置，但我看不到在模拟器用户界面的任何更改。

main.xml中

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="vertical" android:layout_width="match_parent" 
    android:layout_height="match_parent"> 
    <TableLayout 
     android:id="@+id/LightSignal" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:layout_centerInParent="true" 
     android:layout_marginTop="23dp" 
     android:stretchColumns="*" > 

     <TableRow 
      android:id="@+id/tableRow1" 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:weightSum="1" > 

      <TextView 
       android:id="@+id/Left" 
       android:layout_width="0dp" 
       android:layout_height="wrap_content" 
       android:paddingLeft="8dp" 
       android:textColor="#FFF000" 
       android:background = "#000000" 
       android:layout_column="0" 
       /> 

      <TextView 
       android:id="@+id/Right" 
       android:paddingLeft="4dp" 
       android:layout_width="0dp" 
       android:layout_height="wrap_content" 
       android:textColor="#FFF000" 
       android:background = "#000000" 
       android:layout_column="1" 
       /> 
     </TableRow> 
    </TableLayout> 

</LinearLayout> 

MainActivity.cs

using System; 

using Android.App; 
using Android.Content; 
using Android.Content.PM; 
using Android.Runtime; 
using Android.Views; 
using Android.Widget; 
using Android.OS; 
using System.Collections.Generic; 
using Android.Graphics; 

namespace Core.Droid 
{ 
    [Activity (Label = "Core.Droid", Icon = "@drawable/icon", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)] 
    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity 
    { 

     bool IsRed; 
     protected override void OnCreate (Bundle bundle) 
     { 
      base.OnCreate (bundle); 

      global::Xamarin.Forms.Forms.Init (this, bundle); 
      var app = new App(); 
      LoadApplication(app); 
      this.SetContentView(Resource.Layout.Main); 

      System.Timers.Timer timer = new System.Timers.Timer(); 
      timer.Interval = 1000; 
      timer.Elapsed += ColorFlip; 
      timer.Enabled = true; 

     } 

     private void ColorFlip(object sender, System.Timers.ElapsedEventArgs e) 
     { 
      var left = FindViewById<TextView> (Resource.Id.Left); 
      var right = FindViewById<TextView> (Resource.Id.Right); 

      if (IsRed) { 
       left.SetBackgroundColor (Color.Black); 
       right.SetBackgroundColor (Color.Blue); 
       IsRed = false; 
      }else { 
       left.SetBackgroundColor (Color.Red); 
       right.SetBackgroundColor (Color.Black); 
       IsRed = true; 
      } 
     } 
    } 
} 

我假设我需要强制UI更新后，我改变颜色，我该如何解决这个问题？

Answer 1

使用RunOnUiThread：

private void ColorFlip(object sender, System.Timers.ElapsedEventArgs e) 
{ 
    RunOnUiThread (() => { 
     var left = FindViewById<TextView> (Resource.Id.Left); 
     var right = FindViewById<TextView> (Resource.Id.Right); 

     if (IsRed) { 
      left.SetBackgroundColor (Color.Black); 
      right.SetBackgroundColor (Color.Blue); 
      IsRed = false; 
     } else { 
      left.SetBackgroundColor (Color.Red); 
      right.SetBackgroundColor (Color.Black); 
      IsRed = true; 
     } 
    }); 
}