HttpClient的进度栏

小编典典

HttpClient的进度栏

我有一个文件下载功能：

        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？也许我可以到目前为止写出作家的字节数？或者其他的东西？

PS我不能使用DownloadOperation（背景传输），因为来自服务器的数据需要证书-并且DownloadOperations中不存在此功能。

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2020-05-19

共1个答案

小编典典

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

但是，如果由于某种原因您想坚持使用System.Net，则需要实现自己的进度。

删除DataWriter，删除InMemoryRandomAccessStream和
添加HttpCompletionOption.ResponseHeadersRead到GetAsync调用，以便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：

// 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();

2020-05-19