OpenReadTaskAsync無法正常工作？

所以我試圖讓一個後臺代理每30秒下載一個映像。當它被調用時，它調用這個函數`DownloadImageFromServer'。使用斷點，我發現它碰到了OpenReadTaskAsync函數調用，但似乎跳過了其餘的代碼（斷點從來沒有命中）。隨着它不下載圖像的事實。任何想法是什麼導致這一點？OpenReadTaskAsync無法正常工作？

 private async void DownloadImagefromServer(string imgUrl) 
    { 
     Debug.WriteLine("Attempting to Get Image from Server..."); 
     WebClient client = new WebClient(); 



    var result = await client.OpenReadTaskAsync(new Uri(imgUrl, UriKind.Absolute)); 
    //============================================================ 
    //THE BELOW CODE IS NEVER HIT WHEN PUT WITH BREAKPOINTS 
    /============================================================= 
      BitmapImage bitmap = new BitmapImage(); 
      bitmap.SetSource(result); 

      // Create a filename for JPEG file in isolated storage. 
      String tempJPEG = "DownloadedWalleper.jpg"; 

      // Create virtual store and file stream. Check for duplicate tempJPEG files. 
      using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication()) 
      { 
       if (myIsolatedStorage.FileExists(tempJPEG)) 
       { 
        myIsolatedStorage.DeleteFile(tempJPEG); 
       } 

       IsolatedStorageFileStream fileStream = myIsolatedStorage.CreateFile(tempJPEG); 

       StreamResourceInfo sri = null; 
       Uri uri = new Uri(tempJPEG, UriKind.Relative); 
       sri = Application.GetResourceStream(uri); 


       WriteableBitmap wb = new WriteableBitmap(bitmap); 

       // Encode WriteableBitmap object to a JPEG stream. 
       Extensions.SaveJpeg(wb, fileStream, wb.PixelWidth, wb.PixelHeight, 0, 85); 


       fileStream.Close(); 
      } 
      LockScreenChange("DownloadedWalleper.jpg", false); 


    }

來源

2013-12-08 JcKelley

不要使用'異步void'。 – SLaks

我會用什麼來代替？ – JcKelley

http://msdn.microsoft.com/en-us/magazine/jj991977.aspx – SLaks

如果您使用的是.NET 4.5，你可以做一個新webclient並下載文件與異步

例子：

private void btnDownload_Click(object sender, EventArgs e) 
{ 
    WebClient webClient = new WebClient(); 
    webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed); 
    webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged); 
    webClient.DownloadFileAsync(new Uri("http://example.com/myfile.txt"), @"c:\myfile.txt"); 
}

來源

2015-07-08 15:47:45 DustyJello

OpenReadTaskAsync無法正常工作？

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