在Windows Phone 8.1中的背景任务显示对话框的问题

Question

我有这个代码执行httpwebrequest和响应背景方法，我只想显示对话框的信息，当下载邮编崩溃，我的代码输入在此捕获...

private void DoSincroFit() 
    { 
     HttpWebRequest request = HttpWebRequest.CreateHttp(url); 
     request.BeginGetResponse(new AsyncCallback(playResponseAsync), request); 
    } 

    public async void playResponseAsync(IAsyncResult asyncResult) 
    { 
     //Declaration of variables 
     HttpWebRequest webRequest = (HttpWebRequest)asyncResult.AsyncState; 

     try 
     { 
      string fileName = "sincrofit.rar"; 

      using (HttpWebResponse webResponse = (HttpWebResponse)webRequest.EndGetResponse(asyncResult)) 
      { 
       byte[] buffer = new byte[1024]; 


       var newZipFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting); 
       var newZipFile = await KnownFolders.DocumentsLibrary.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting); 

       using (var writeStream = await newZipFile.OpenAsync(FileAccessMode.ReadWrite)) 
       { 
        using (var outputStream = writeStream.GetOutputStreamAt(0)) 
        { 
         using (var dataWriter = new DataWriter(outputStream)) 
         { 
          using (Stream input = webResponse.GetResponseStream()) 
          { 
           var totalSize = 0; 
           for (int size = input.Read(buffer, 0, buffer.Length); size > 0; size = input.Read(buffer, 0, buffer.Length)) 
           { 
            dataWriter.WriteBytes(buffer); 
            totalSize += size; //get the progress of download 
           } 
           await dataWriter.StoreAsync(); 
           await outputStream.FlushAsync(); 
           dataWriter.DetachStream(); 
          } 
         } 
        } 
       } 

      } 
     } 
     catch 
     { 
      SMethods.Message_Dialog("Download has stopped!","Error"); 
     } 
    } 

但是，当我的代码执行这种方法，从这个类：

class StandarMethods 
{ 
public async void Message_Dialog(string text, string title) 
    { 
     //Declaration of variables 
     MessageDialog MDialog = new MessageDialog(text, title); 

     await MDialog.ShowAsync(); 
    } 
} 

最后我的应用程序崩溃时，尝试执行：

await MDialog.ShowAsync(); 

这是在后台任务等待...有人可以帮助我吗？有可能使用事件处理程序？为什么？怎么样？提前致谢！

Answer 1

解决，我的最终代码是在这里：

private CoreDispatcher dispatcher; 

    private void DoSincroFit() 
    { 
     HttpWebRequest request = HttpWebRequest.CreateHttp(url); 

     //Add headers to request 
     request.Headers["Type"] = "sincrofit"; 
     request.Headers["Device"] = "1"; 
     request.Headers["Version"] = "0.000"; 
     request.Headers["Os"] = "WindowsPhone"; 

     dispatcher = CoreWindow.GetForCurrentThread().Dispatcher; 
     request.BeginGetResponse(new AsyncCallback(playResponseAsync), request); 
    } 

    public async void playResponseAsync(IAsyncResult asyncResult) 
    { 
     //Declaration of variables 
     HttpWebRequest webRequest = (HttpWebRequest)asyncResult.AsyncState; 

     try 
     { 
      //For download file with stream 
      //http://social.msdn.microsoft.com/Forums/windowsapps/en-US/de96a61c-e089-4595-8349-612be5d23ee6/download-file-with-httpwebrequest?forum=winappswithcsharp 
      string fileName = "sincrofit.rar"; 

      using (HttpWebResponse webResponse = (HttpWebResponse)webRequest.EndGetResponse(asyncResult)) 
      { 
       byte[] buffer = new byte[1024]; 

       //For acces Local folder of phone device 
       //http://social.msdn.microsoft.com/Forums/windowsapps/en-US/ec99721c-6565-4ce9-b6cc-218f2265f9c7/what-is-the-uri-of-an-isolatedstorage-file?forum=wpdevelop 
       var newZipFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting); 

       using (var writeStream = await newZipFile.OpenAsync(FileAccessMode.ReadWrite)) 
       { 
        using (var outputStream = writeStream.GetOutputStreamAt(0)) 
        { 
         using (var dataWriter = new DataWriter(outputStream)) 
         { 
          using (Stream input = webResponse.GetResponseStream()) 
          { 
           var totalSize = 0; 

           for (int size = input.Read(buffer, 0, buffer.Length); size > 0; size = input.Read(buffer, 0, buffer.Length)) 
           { 
            dataWriter.WriteBytes(buffer); 
            totalSize += size; //get the progress of download 

            dispatcher.RunAsync(CoreDispatcherPriority.Normal, async() => 
            { 
             //Declaration of variables 
             pBar.Value = sizeFit/totalSize * 100; 
            }); 
           } 
           await dataWriter.StoreAsync(); 
           await outputStream.FlushAsync(); 
           dataWriter.DetachStream(); 
          } 
         } 
        } 
       } 

      } 
     } 
     catch 
     { 
      dispatcher.RunAsync(CoreDispatcherPriority.Normal, async() => 
      { 
       //Declaration of variables 
       SMethods.Message_Dialog("Download has stopped!", "Error"); 
      }); 
     } 
    } 

感谢您的时间@loop！

Answer 2

Merli你的问题是你正试图从一个背景胎面访问UI线程来显示对话框，用户因此使用调度这个基本的例子是： -

// This is for silverlight part 
    Deployment.Current.Dispatcher.BeginInvoke(delegate 
    { 
     var mbr = MessageBox.Show("Are you sure you want to leave this page?", "Warning",  
     MessageBoxButton.OKCancel); 

     if(mbr == MessageBoxResult.OK) 
     { OK pressed } 
     else 
     { Cancel pressed } 

    }); 

对于WinRT的一部分 -

CoreDispatcher dispatcher = CoreWindow.GetForCurrentThread().Dispatcher; 
    dispatcher.RunAsync(CoreDispatcherPriority.Normal, async()=>{ 
      // UI code goes here 
      //Declaration of variables 
     MessageDialog MDialog = new MessageDialog(text, title); 
     await MDialog.ShowAsync(); 
    }); 

Answer 3

我的最终代码：

private void DoSincroFit() 
    { 
     HttpWebRequest request = HttpWebRequest.CreateHttp(url); 

     //Add headers to request 
     request.Headers["Type"] = "sincrofit"; 
     request.Headers["Device"] = "1"; 
     request.Headers["Version"] = "0.000"; 
     request.Headers["Os"] = "WindowsPhone"; 

     request.BeginGetResponse(new AsyncCallback(playResponseAsync), request); 
    } 

    public async void playResponseAsync(IAsyncResult asyncResult) 
    { 
     //Declaration of variables 
     HttpWebRequest webRequest = (HttpWebRequest)asyncResult.AsyncState; 

     try 
     { 
      string fileName = "sincrofit.rar"; 

      using (HttpWebResponse webResponse = (HttpWebResponse)webRequest.EndGetResponse(asyncResult)) 
      { 
       byte[] buffer = new byte[1024]; 
       var newZipFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting); 

       using (var writeStream = await newZipFile.OpenAsync(FileAccessMode.ReadWrite)) 
       { 
        using (var outputStream = writeStream.GetOutputStreamAt(0)) 
        { 
         using (var dataWriter = new DataWriter(outputStream)) 
         { 
          using (Stream input = webResponse.GetResponseStream()) 
          { 
           var totalSize = 0; 
           for (int size = input.Read(buffer, 0, buffer.Length); size > 0; size = input.Read(buffer, 0, buffer.Length)) 
           { 
            dataWriter.WriteBytes(buffer); 
            totalSize += size; //get the progress of download 
           } 
           await dataWriter.StoreAsync(); 
           await outputStream.FlushAsync(); 
           dataWriter.DetachStream(); 
          } 
         } 
        } 
       } 

      } 
     } 
     catch 
     { 
      dispatcher = CoreWindow.GetForCurrentThread().Dispatcher; //CRASH IN THIS LINE! 
      dispatcher.RunAsync(CoreDispatcherPriority.Normal, async() => 
      { 
       //Declaration of variables 
       SMethods.Message_Dialog("Download has stopped!", "Error"); 
      }); 
     } 
    } 

这是我的照片：

谢谢大家！