Convert AsyncCallback to awaitable task

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

来源：https://stackoverflow.com/questions/28526857/convert-asynccallback-to-awaitable-task