在ScheduledTaskAgent中使用HttpWebRequest

ScheduledTaskAgent是WP7的后台代理，可以利用它在后台执行某些操作，比如更新Live Tile。可以用推送通知来更新Live Tile，但某些实时性要求不高的任务可以用后台代理来做。

但后台代理有诸多限制，比如某些API就不能使用。http://msdn.microsoft.com/zh-cn/library/hh202962(v=vs.92).aspx 这里有后台代理不支持的API列表，比如摄像头这些设备就无法在后台代理中使用。需要注意的API：

GeoCoordinateWatcher	此 API 用于获取设备的地理坐标，支持在后台代理中使用，但它使用缓存的位置值而不是实时数据。设备每 15 分钟更新缓存的位置值。
Mutex 类	应该使用 Mutex 类同步对在前台应用程序和后台代理之间共享的资源（如独立存储中的文件）的访问。
ShellToast 类	该类可以用于从正在运行的后台代理弹出 Toast 通知。
ShellTile 类的 Update(ShellTileData) 方法 ShellTile 类的 Delete()()()() 方法 ShellTile 类的 ActiveTiles 属性。	这些方法可以用于修改正在运行的后台代理中的 shell 磁贴。请注意，不能在后台代理中创建 shell 磁贴。
HttpWebRequest 类	该类允许您从正在运行的后台代理进行 Web 请求。

 

有HttpWebRequest类就可以实现目的了，从网络请求数据，用ShellTile的Update()方法更新Live Tile即可。在使用中也发现了一些问题，记录下来。

 

首先要实现Live Tile。http://msdn.microsoft.com/zh-cn/library/hh202979(v=vs.92).aspx 此页面演示了如何创建、修改Live Tile。我的目的是创建显示货币汇率的Live Tile，代码如下：

/// <summary>
/// Handles the Click event of the menuPinToStart control.固定到开始屏幕
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">The <see cref="System.Windows.RoutedEventArgs"/> instance containing the event data.</param>
        private void menuPinToStart_Click(object sender, RoutedEventArgs e)
        {
            MenuItem menuItem = sender as MenuItem;
            CurrEntity currEntity = menuItem.DataContext as CurrEntity;

            if (currEntity.CurrBase.Code != currEntity.CurrTarget.Code)
            {
                StringBuilder sb = new StringBuilder();
                sb.AppendFormat(CultureInfo.InvariantCulture, paratemplate, currEntity.CurrBase.Code, currEntity.CurrTarget.Code);

                // Look to see whether the Tile already exists and if so, don't try to create it again.
                ShellTile TileToFind = ShellTile.ActiveTiles.FirstOrDefault(x => x.NavigationUri.ToString().Contains("MainPage.xaml?" + sb.ToString()));

                // Create the Tile if we didn't find that it already exists.
                if (TileToFind == null)
                {
                    // Create the Tile object and set some initial properties for the Tile.
// The Count value of 12 shows the number 12 on the front of the Tile. Valid values are 1-99.
// A Count value of 0 indicates that the Count should not be displayed.
                    StandardTileData NewTileData = new StandardTileData
                    {
                        BackgroundImage = new Uri("TileBackground.png", UriKind.Relative),
                        Title = "1" + currEntity.CurrBase.Code + "=" + currEntity.Rate.ToString() + currEntity.CurrTarget.Code,
                        Count = 0,
                        BackTitle = currEntity.TradeDate.ToString(),
                        BackContent = "1" + currEntity.CurrBase.Code + " = " + currEntity.Rate.ToString() + currEntity.CurrTarget.Code,
                        //BackBackgroundImage = new Uri("Blue.jpg", UriKind.Relative)
                    };
                    // Create the Tile and pin it to Start. This will cause a navigation to Start and a deactivation of our application.
                    ShellTile.Create(new Uri("/MainPage.xaml?" + sb.ToString(), UriKind.Relative), NewTileData);
                }
            }
        }

为了区别每种货币，将货币代码附在ShellTile的NavigationUri属性里，这样可以在后台代理中取出相应的货币。

 

然后创建后台代理。新建一个后台代理项目。http://msdn.microsoft.com/zh-cn/library/hh202941(v=vs.92).aspx 这个页面演示了如何使用后台代理弹出Toast通知，为了更新Live Tile，需要改动一下。关键代码如下：

protected override void OnInvoke(ScheduledTask task)
{
  //TODO: Add code to perform your task in background
  string toastMessage = "";

  // If your application uses both PeriodicTask and ResourceIntensiveTask
// you can branch your application code here. Otherwise, you don't need to.
  if (task is PeriodicTask)
  {
    // Execute periodic task actions here.
    toastMessage = "Periodic task running.";
  }
  else
  {
    // Execute resource-intensive task actions here.
    toastMessage = "Resource-intensive task running.";
  }

  // Launch a toast to show that the agent is running.
// The toast will not be shown if the foreground application is running.
  ShellToast toast = new ShellToast();
  toast.Title = "Background Agent Sample";
  toast.Content = toastMessage;
  toast.Show();

  // If debugging is enabled, launch the agent again in one minute.
#if DEBUG_AGENT
  ScheduledActionService.LaunchForTest(task.Name, TimeSpan.FromSeconds(60));
#endif

  // Call NotifyComplete to let the system know the agent is done working.
  NotifyComplete();
}

把其中的代码换成更新Live Tile的代码即可。首先要异步请求数据，然后更新Live Tile。异步请求的代码如下：

/// <summary>
/// State information for our BeginGetResponse async call
/// </summary>
        public class RequestState
        {
            public HttpWebRequest AsyncRequest { get; set; }
            public HttpWebResponse AsyncResponse { get; set; }
        }

        
        private void ConvertCurrencyByHttpWebRequest()
        {
            //先判断网络是否可用
            bool networkIsAvailable = Microsoft.Phone.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable();//当前网络是否可用  
            if (networkIsAvailable)
            {
                //把当前要转换的货币转换成uri
                StringBuilder sb = new StringBuilder();

                foreach (CurrEntity data in this.currEntityList)
                {
                    try
                    {
                        //do something
                    }
                    catch
                    { 
                    }
                }

                string url = String.Format(CultureInfo.InvariantCulture, currUrl, sb.ToString());
                Uri uri = new Uri(url);

                //开始异步调用
                HttpWebRequest myRequest = (HttpWebRequest)WebRequest.Create(uri);
                //设置异步请求状态
                RequestState requestState = new RequestState();
                requestState.AsyncRequest = myRequest;
                //开始对 Internet 资源的异步请求。
//IAsyncResult result = (IAsyncResult)req.BeginGetResponse(new AsyncCallback(ResponseCallback), req);//返回异步操作的状态
                myRequest.BeginGetResponse(new AsyncCallback(ResponseCallback), requestState);

                
            }
        }

       

        private void ResponseCallback(IAsyncResult asyncResult)
        {
            RequestState requestState = (RequestState)asyncResult.AsyncState;
            //获取异步操作返回的的信息
            HttpWebRequest myRequest = (HttpWebRequest)requestState.AsyncRequest;
            //结束对 Internet 资源的异步请求
            requestState.AsyncResponse = (HttpWebResponse)myRequest.EndGetResponse(asyncResult);
            //WebResponse response = request.EndGetResponse(result);

            using (Stream stream = requestState.AsyncResponse.GetResponseStream())
            using (StreamReader respReader = new StreamReader(stream))
            {
                try
                {
                    //do something
                    //更新Live Tile
                    UpdateTile();
                }
                finally
                {
                    respReader.Close();
                }
  
            }

        }

更新Live Tile：

/// <summary>
/// Updates the tile.更新LiveTile
/// </summary>
        private void UpdateTile()
        {
            //throw new NotImplementedException();
            foreach (CurrEntity currEntity in currEntityList)
            {
                StringBuilder sb = new StringBuilder();
                sb.AppendFormat(CultureInfo.InvariantCulture, paratemplate, currEntity.CurrBase.Code, currEntity.CurrTarget.Code);
                //找出对应的Tile
                ShellTile TileToFind = ShellTile.ActiveTiles.FirstOrDefault(x => x.NavigationUri.ToString().Contains("MainPage.xaml?" + sb.ToString()));
                if (TileToFind != null)
                {
                    StandardTileData NewTileData = new StandardTileData
                    {
                        BackgroundImage = new Uri("TileBackground.png", UriKind.Relative),
                        Title = "1" + currEntity.CurrBase.Code + "=" + currEntity.Rate.ToString() + currEntity.CurrTarget.Code,
                        Count = 0,
                        BackTitle = currEntity.TradeDate.ToString(),
                        BackContent = "1" + currEntity.CurrBase.Code + " = " + currEntity.Rate.ToString() + currEntity.CurrTarget.Code,
                        //BackBackgroundImage = new Uri("Blue.jpg", UriKind.Relative)
                    };
                    TileToFind.Update(NewTileData);

                }
            }
            //ShellToast toast = new ShellToast();
//toast.Title = "test";
//toast.Content = "update success!";
//toast.Show();
        }

将后台代理的代码改为：

protected override void OnInvoke(ScheduledTask task)
        {
            //TODO: Add code to perform your task in background
//string toastTitle = "Periodic";
            this.AdjustToLocalTime = true;
            this.currEntityList = new List<CurrEntity>();
            // If your application uses both PeriodicTask and ResourceIntensiveTask
// you can branch your application code here. Otherwise, you don't need to.
//if (task is PeriodicTask)
//{
//// Execute periodic task actions here.
//    toastTitle = "Periodic ";
//}
//else
//{
//// Execute resource-intensive task actions here.
//    toastTitle = "Resource-intensive ";
//}

            
            var query = from x in ShellTile.ActiveTiles where x.NavigationUri.ToString().Contains("?s=") select x;
            List<ShellTile> shellTileList = query.ToList();
            if (shellTileList.Count > 0)
            {
                //foreach (ShellTile tile in query.ToList())
                for (int i = 0; i < shellTileList.Count; i++)
                {
                    ShellTile tile = shellTileList[i] as ShellTile;
                    string strCode = tile.NavigationUri.ToString().Substring(tile.NavigationUri.ToString().IndexOf("=") + 1, 6);
                    CurrEntity currEntity = new CurrEntity();
                    currEntity.CurrBase = new CurrDescEntity(strCode.Substring(0, 3), "");
                    currEntity.CurrTarget = new CurrDescEntity(strCode.Substring(3, 3), "");
                    currEntity.CurrencyAmount = 0;
                    currEntity.IsInversion = false;
                    currEntity.IsStandard = false;
                    currEntity.Rate = 0;
                    currEntity.TradeDate = System.DateTime.Now;
                    currEntityList.Add(currEntity);
                }
                //调用HttpWebRequest更新数据
                this.ConvertCurrencyByHttpWebRequest();
            }



            // If debugging is enabled, launch the agent again in one minute.
#if DEBUG_AGENT
            ScheduledActionService.LaunchForTest(task.Name, TimeSpan.FromSeconds(60));
#endif
            
            NotifyComplete();
        }

从Live Tile的NavigationUri中读取参数，并调用HttpWebRequest进行异步请求。

然后运行一下，奇怪的是，总是无法更新。断点调试，发现异步请求 myRequest.BeginGetResponse(new AsyncCallback(ResponseCallback), requestState); 执行了，但总是无法获取返回数据。好像ResponseCallback根本就没有执行。

查看后台代理的OnInvoke方法，发现在调用异步请求后，执行了一句　NotifyComplete();

这个方法意思是：通知操作系统，代理已完成其针对当前代理调用的预定任务。

也就是说，发起异步请求后，还没有等到异步返回结果，就通知系统代理已经完成任务了，导致ResponseCallback没有执行。

因此把NotifyComplete()转移到异步返回数据之后即可。

2012.1.20补充：http://forums.create.msdn.com/forums/p/90294/587823.aspx#587823

可以写成下面这样：

Move NotifyComplete() into your anonymous delegate like this:
1    protected override void OnInvoke(ScheduledTask task)  
2    {  
3            // tried also Create instead of CreateHttp  
4        var request = (HttpWebRequest)HttpWebRequest.CreateHttp(new Uri("http://www.1112.net/lastpage.html"));  
5     
6     
7            // breakpoint here #1  
8        request.BeginGetResponse((ar) =>  
9        {  
10                    // breakpoint here #2  
11            try 
12            {  
13                using (StreamReader reader = new StreamReader(request.EndGetRequestStream(ar)))  
14                {  
15                    // breakpoint here #3  
16                    string result = reader.ReadToEnd();  
17                }  
18            }  
19            catch (Exception)  
20            {  
21                // breakpoint here #4  
22            }  
23            // call it here.  
24            NotifyComplete();  
25        }, null);  
26     
27        // DON'T call this here.  
28        // NotifyComple