带有 HttpClient 的进度条 [英] Progress bar with HttpClient

问题描述

我有一个文件下载器功能:

i have a file downloader function:

        HttpClientHandler aHandler = new HttpClientHandler();
        aHandler.ClientCertificateOptions = ClientCertificateOption.Automatic;
        HttpClient aClient = new HttpClient(aHandler);
        aClient.DefaultRequestHeaders.ExpectContinue = false;
        HttpResponseMessage response = await aClient.GetAsync(url);
        InMemoryRandomAccessStream randomAccessStream = new InMemoryRandomAccessStream();

        // To save downloaded image to local storage
        var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
        filename, CreationCollisionOption.ReplaceExisting);
        var fs = await imageFile.OpenAsync(FileAccessMode.ReadWrite);
        DataWriter writer = new DataWriter(fs.GetOutputStreamAt(0));

        writer.WriteBytes(await response.Content.ReadAsByteArrayAsync());

        await writer.StoreAsync();
        //current.image.SetSource(randomAccessStream);
        writer.DetachStream();
        await fs.FlushAsync();

如何实现进度条功能?也许我可以得到到目前为止写入的 writers 字节?或者什么?

How can i realize progress bar functionality? Maybe i can get the writers bytes written so far? Or something?

P.S.我无法使用 DownloadOperation(后台传输)，因为来自服务器的数据请求证书 - 而 DownloadOperations 中不存在此功能.

推荐答案

最好的方法是使用 Windows.Web.Http.HttpClient 而不是 System.Net.Http.HttpClient.第一个支持进步.

The best way to go is using Windows.Web.Http.HttpClient instead of System.Net.Http.HttpClient. The first one supports progress.

但如果出于某种原因您想坚持使用 System.Net，则需要实现自己的进步.

But if for some reason you want to stick to the System.Net one, you will need to implement your own progress.

移除DataWriter，移除InMemoryRandomAccessStream 并将添加HttpCompletionOption.ResponseHeadersRead 到GetAsync 调用 因此它在收到标头后立即返回，而不是在收到整个响应时返回.即:

Remove the DataWriter, remove the InMemoryRandomAccessStream and add HttpCompletionOption.ResponseHeadersRead to GetAsync call so it returns as soon as headers are received, not when the whole response is received. I.e.:

// Your original code.
HttpClientHandler aHandler = new HttpClientHandler();
aHandler.ClientCertificateOptions = ClientCertificateOption.Automatic;
HttpClient aClient = new HttpClient(aHandler);
aClient.DefaultRequestHeaders.ExpectContinue = false;
HttpResponseMessage response = await aClient.GetAsync(
    url,
    HttpCompletionOption.ResponseHeadersRead); // Important! ResponseHeadersRead.

// To save downloaded image to local storage
var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
    filename,
    CreationCollisionOption.ReplaceExisting);
var fs = await imageFile.OpenAsync(FileAccessMode.ReadWrite);

// New code.
Stream stream = await response.Content.ReadAsStreamAsync();
IInputStream inputStream = stream.AsInputStream();
ulong totalBytesRead = 0;
while (true)
{
    // Read from the web.
    IBuffer buffer = new Windows.Storage.Streams.Buffer(1024);
    buffer = await inputStream.ReadAsync(
        buffer,
        buffer.Capacity,
        InputStreamOptions.None);

    if (buffer.Length == 0)
    {
        // There is nothing else to read.
        break;
    }

    // Report progress.
    totalBytesRead += buffer.Length;
    System.Diagnostics.Debug.WriteLine("Bytes read: {0}", totalBytesRead);

    // Write to file.
    await fs.WriteAsync(buffer);
}
inputStream.Dispose();
fs.Dispose();

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