问题:

I'm trying to implement the download of a given url. By the way my code is:

private string url; private StorageFile outputFile;  public void download() {     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     {          using (HttpWebResponse webResponse = (HttpWebResponse)webRequest.EndGetResponse(asyncResult))         {             byte[] buffer = new byte[1024];              using (var writeStream = await outputFile.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();                         }                     }                 }             }             Debug.WriteLine("Finished");         }     }     catch     {      } } }

I'd like my download method to have the following signature

Task<bool> download();

(Returning true if the download succeeded and false otherwise)

making it an awaitable task. But I do not master C# and don't know how to do it. Can you help me?

Thanks

回答1:

Task.Factory.FromAsync is there to simplify usage of old asyncronous pattern

public async Task<bool> download() {     HttpWebRequest request = HttpWebRequest.CreateHttp(url);     HttpWebResponse webResponse = (HttpWebResponse)await Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse, request.EndGetResponse, request);      try     {         using (webResponse)         {             byte[] buffer = new byte[1024];              using (var writeStream = await outputFile.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();                         }                     }                 }             }             Debug.WriteLine("Finished");         }     }     catch     {         return false;     } } return true; }

But I would use newer HttpClient as suggested

转载请标明出处:Convert AsyncCallback to awaitable task

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