我该如何使用HttpClient PostAsync计算进度？

Question

我该如何使用HttpClient PostAsync计算进度？

6

在我的Windows应用程序中（c#），我需要向服务器上传MultipartFormDataContent（一些字符串内容和一些文件）并在响应中获得一个大文件。问题是，我不能使用BackgroundDownloaders来完成这个任务，我只能使用一个请求。

我使用HttpClient.PostAsync方法：

 using (var client = new HttpClient(httpClientHandler))
            {
                using (var content = new MultipartFormDataContent())
                {
                    content.Add(...); // prepare all strings and files content
                    try
                    {
                        using (var response = await client.PostAsync(url, content))
                        {
                            if (response.StatusCode == HttpStatusCode.OK)
                            {
                                var inputBytes = await response.Content.ReadAsByteArrayAsync();
                                // some operations with inputBytes 
                            }
                            ......
                        }
                    }
                }
            }

我的问题是：我该如何计算此操作的进度？

注意：我的目标是Windows 8。并且我不能使用Windows.Web.Http.HttpClient（最低支持客户端为Windows 8.1）。只能使用System.Net.Http.HttpClient。

- jimpanzer

2个回答

4

WebAPI Client nuget中有一些类可以完成这个任务。请查看ProgressMessageHandler。它是一个PCL库，所以Windows Store应用程序应该可以正常运行。

- Darrel Miller

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可以查看英文原文，
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- Medeni Baykal · Accepted Answer

我遇到了相同的问题。我通过实现自定义 HttpContent 解决了这个问题。我使用这个对象来跟踪上传进度的百分比，你可以添加一个事件并监听它。你应该自定义 SerializeToStreamAsync 方法。

internal class ProgressableStreamContent : HttpContent
{
    private const int defaultBufferSize = 4096;

    private Stream content;
    private int bufferSize;
    private bool contentConsumed;
    private Download downloader;

    public ProgressableStreamContent(Stream content, Download downloader) : this(content, defaultBufferSize, downloader) {}

    public ProgressableStreamContent(Stream content, int bufferSize, Download downloader)
    {
        if(content == null)
        {
            throw new ArgumentNullException("content");
        }
        if(bufferSize <= 0)
        {
            throw new ArgumentOutOfRangeException("bufferSize");
        }

        this.content = content;
        this.bufferSize = bufferSize;
        this.downloader = downloader;
    }

    protected override Task SerializeToStreamAsync(Stream stream, TransportContext context)
    {
        Contract.Assert(stream != null);

        PrepareContent();

        return Task.Run(() =>
        {
            var buffer = new Byte[this.bufferSize];
            var size = content.Length;
            var uploaded = 0;

            downloader.ChangeState(DownloadState.PendingUpload);

            using(content) while(true)
            {
                var length = content.Read(buffer, 0, buffer.Length);
                if(length <= 0) break;

                downloader.Uploaded = uploaded += length;

                stream.Write(buffer, 0, length);

                downloader.ChangeState(DownloadState.Uploading);
            }

            downloader.ChangeState(DownloadState.PendingResponse);
        });
    }

    protected override bool TryComputeLength(out long length)
    {
        length = content.Length;
        return true;
    }

    protected override void Dispose(bool disposing)
    {
        if(disposing)
        {
            content.Dispose();
        }
        base.Dispose(disposing);
    }


    private void PrepareContent()
    {
        if(contentConsumed)
        {
            // If the content needs to be written to a target stream a 2nd time, then the stream must support
            // seeking (e.g. a FileStream), otherwise the stream can't be copied a second time to a target 
            // stream (e.g. a NetworkStream).
            if(content.CanSeek)
            {
                content.Position = 0;
            }
            else
            {
                throw new InvalidOperationException("SR.net_http_content_stream_already_read");
            }
        }

        contentConsumed = true;
    }
}

仅供参考：

public interface IDownload
{
    event EventHandler<DownloadStateEventArgs> StateChanged;
    event EventHandler<DownloadStateEventArgs> Completed;

    DownloadState State { get; }
    Guid Id { get; }
    string Uri { get; }
    long Filesize { get; }
    long Downloaded { get; }

    Task DownloadAsync();
}