如何使用 C# HttpClient PostAsync 显示上传进度

Question

我正在使用 Xamarin PCL 创建适用于 Android 和 iOS 的文件上传应用程序，并且我已设法实现文件上传和某种进度条，但它无法正常工作。

我看到了一些关于显示下载进度的堆栈溢出的答案，但我想通知我的用户有关上传进度但没有找到任何解决方案。

这是我的代码：

public static async Task<string> PostFileAsync (Stream filestream, string filename, int filesize) {
        var progress = new System.Net.Http.Handlers.ProgressMessageHandler ();

        //Progress tracking
        progress.HttpSendProgress += (object sender, System.Net.Http.Handlers.HttpProgressEventArgs e) => {
            int progressPercentage = (int)(e.BytesTransferred*100/filesize);
            //Raise an event that is used to update the UI
            UploadProgressMade(sender, new System.Net.Http.Handlers.HttpProgressEventArgs(progressPercentage, null, e.BytesTransferred, null));
        };

        using (var client = HttpClientFactory.Create(progress)) {
            using (var content = new MultipartFormDataContent ("------" + DateTime.Now.Ticks.ToString ("x"))) {
                content.Add (new StreamContent (filestream), "Filedata", filename);
                using (var message = await client.PostAsync ("http://MyUrl.example", content)) {
                    var result = await message.Content.ReadAsStringAsync ();
                    System.Diagnostics.Debug.WriteLine ("Upload done");
                    return result;
                }
            }
        }
    }

显示了某种进度，但是当进度达到 100% 时，文件还没有上传。在我收到最后一条进度消息后的一段时间内，也会打印消息“上传完成”。

也许进度是显示从设备发出的字节，而不是尚未上传的字节，所以当它说，它是 100% 时，所有字节都刚刚发出，但还没有被服务器接收？

编辑：尝试了这个解决方案：https://forums.xamarin.com/discussion/56716/plans-to-add-webclient-to-pcl，效果更好。

Answer 1

试试这样的：

我遇到了同样的问题。我通过实现自定义HttpContent 来修复它。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。您应该自定义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;
    }
}

---

参考：

• https://github.com/paulcbetts/ModernHttpClient/issues/80
• Progress bar for HttpClient uploading
• https://forums.xamarin.com/discussion/18649/best-practice-to-upload-image-selected-to-a-web-api

Answer 2

上传进度文件的最简单方法

您可以通过跟踪您要上传的文件的FileStream 的Position 来获得准确的进度。

这演示了如何做到这一点。

FileStream fileToUpload = File.OpenRead(@"C:\test.mp3");

HttpContent content = new StreamContent(fileToUpload);
HttpRequestMessage msg = new HttpRequestMessage{
    Content=content,
    RequestUri = new Uri(--yourUploadURL--)
}

bool keepTracking = true; //to start and stop the tracking thread
new Task(new Action(() => { progressTracker(fileToUpload, ref keepTracking); })).Start();
var result = httpClient.SendAsync(msg).Result;
keepTracking = false; //stops the tracking thread

而progressTracker()函数定义为

void progressTracker(FileStream streamToTrack, ref bool keepTracking)
{
    int prevPos = -1;
    while (keepTracking)
    {
        int pos = (int)Math.Round(100 * (streamToTrack.Position / (double)streamToTrack.Length));
        if (pos != prevPos)
        {
            Console.WriteLine(pos + "%");

        }
        prevPos = pos;

        Thread.Sleep(100); //update every 100ms
    }
}

Answer 3

这是因为你做错了数学。

更改：int progressPercentage = (int)(e.BytesTransferred*100/filesize);

收件人：int progressPercentage = (int)(e.BytesTransferred/filesize) *100;

改用此代码：

    double bytesOut = double.Parse(e.BytesTransferred.ToString());
        double totalBytes = double.Parse(filesize.ToString());
        double percentage = bytesOut / totalBytes * 100;

或者你可以简单地使用e.ProgressPercentage