從wp7的背景下載網絡文件

Question

我正在寫一個應用程序在c＃wp7：2頁[mainpage，secondpage]。
應用程序從主頁面開始，然後用戶可以導航到第二頁中的第二頁（使用NavigationService.Navigate）。

第二頁WebClient在isolationStorage中下載文件。

我的問題是，當用戶使用後退鍵返回到主頁時，下載會凍結！

有一種方法可以在後臺執行此操作，以便用戶可以導航自由地扔頁面？

這裏是secondpage類的代碼（在click事件中也有一個帶有webClient.OpenReadAsync（uri）的按鈕）。

public partial class SecondPage : PhoneApplicationPage 
{ 
    WebClient webClient = new WebClient(); 
    IsolatedStorageFile Storage = IsolatedStorageFile.GetUserStoreForApplication(); 

    public SecondPage() 
    { 
     InitializeComponent(); 
     webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(webClient_DownloadProgressChanged); 
     webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(webClient_OpenReadCompleted); 
    } 
    void webClient_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e) 
    { 
     try 
     { 
      if (e.Result != null) 
      { 
       string fileName = "download.txt"; 
       IsolatedStorageFileStream f = new IsolatedStorageFileStream(fileName, System.IO.FileMode.Create, Storage); 
       long fileNameLength = (long)e.Result.Length; 
       byte[] byteImage = new byte[fileNameLength]; 
       e.Result.Read(byteImage, 0, byteImage.Length); 
       f.Write(byteImage, 0, byteImage.Length); 
      } 
     } 
     catch (Exception ex) 
     { 
      MessageBox.Show(ex.Message); 
     } 
    } 

    void webClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e) 
    { 
     try 
     { 
      if (ProgressDownload.Value <= ProgressDownload.Maximum) 
      { 
       ProgressDownload.Value = (double)e.ProgressPercentage; 
      } 

     } 
     catch (Exception ex) 
     { 
      MessageBox.Show(ex.Message); 
     } 
    } 
} 

感謝

與BackgroundWorker的類我有這個問題：當我致電webClient.OpenReadAsync的bw_doWork功能（代碼下）結束，因爲調用是異步！所以bw報告completeEvent。

private void bw_DoWork(object sender, DoWorkEventArgs e) 
    { 
     BackgroundWorker worker = sender as BackgroundWorker; 

     WebClient webClient = new WebClient(); 
     webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(webClient_DownloadProgressChanged); 
     webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(webClient_OpenReadCompleted); 


     webClient.OpenReadAsync(new Uri("http://foo.com/asd.txt")); 

    } 

Answer 1

查看Background Transfer APIs - 聽起來像這正是你需要完成你的要求。