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();
我怎样才能实现进度条功能？也许到目前为止我可以写出写入的字节数？或者其他的东西？
附：我无法使用DownloadOperation（后台传输），因为来自服务器的数据请求证书 - 并且DownloadOperations中不存在此功能。
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。
但如果由于某种原因你想坚持使用System.Net，你需要实现自己的进步。
删除DataWriter，删除InMemoryRandomAccessStream并将HttpCompletionOption.ResponseHeadersRead添加到GetAsync调用，以便在收到标题时立即返回，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();
这是一个自包含的类，它将进行下载，并根据Qazxswpoi上的TheBlueSky和this SO answer上的eriksendc的代码报告进度百分比。
this GitHub comment
用法：
public class HttpClientDownloadWithProgress : IDisposable
{
private readonly string _downloadUrl;
private readonly string _destinationFilePath;
private HttpClient _httpClient;
public delegate void ProgressChangedHandler(long? totalFileSize, long totalBytesDownloaded, double? progressPercentage);
public event ProgressChangedHandler ProgressChanged;
public HttpClientDownloadWithProgress(string downloadUrl, string destinationFilePath)
{
_downloadUrl = downloadUrl;
_destinationFilePath = destinationFilePath;
}
public async Task StartDownload()
{
_httpClient = new HttpClient { Timeout = TimeSpan.FromDays(1) };
using (var response = await _httpClient.GetAsync(_downloadUrl, HttpCompletionOption.ResponseHeadersRead))
await DownloadFileFromHttpResponseMessage(response);
}
private async Task DownloadFileFromHttpResponseMessage(HttpResponseMessage response)
{
response.EnsureSuccessStatusCode();
var totalBytes = response.Content.Headers.ContentLength;
using (var contentStream = await response.Content.ReadAsStreamAsync())
await ProcessContentStream(totalBytes, contentStream);
}
private async Task ProcessContentStream(long? totalDownloadSize, Stream contentStream)
{
var totalBytesRead = 0L;
var readCount = 0L;
var buffer = new byte[8192];
var isMoreToRead = true;
using (var fileStream = new FileStream(_destinationFilePath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true))
{
do
{
var bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length);
if (bytesRead == 0)
{
isMoreToRead = false;
TriggerProgressChanged(totalDownloadSize, totalBytesRead);
continue;
}
await fileStream.WriteAsync(buffer, 0, bytesRead);
totalBytesRead += bytesRead;
readCount += 1;
if (readCount % 100 == 0)
TriggerProgressChanged(totalDownloadSize, totalBytesRead);
}
while (isMoreToRead);
}
}
private void TriggerProgressChanged(long? totalDownloadSize, long totalBytesRead)
{
if (ProgressChanged == null)
return;
double? progressPercentage = null;
if (totalDownloadSize.HasValue)
progressPercentage = Math.Round((double)totalBytesRead / totalDownloadSize.Value * 100, 2);
ProgressChanged(totalDownloadSize, totalBytesRead, progressPercentage);
}
public void Dispose()
{
_httpClient?.Dispose();
}
}
结果：
var downloadFileUrl = "http://example.com/file.zip";
var destinationFilePath = Path.GetFullPath("file.zip");
using (var client = new HttpClientDownloadWithProgress(downloadFileUrl, destinationFilePath))
{
client.ProgressChanged += (totalFileSize, totalBytesDownloaded, progressPercentage) => {
Console.WriteLine($"{progressPercentage}% ({totalBytesDownloaded}/{totalFileSize})");
};
await client.StartDownload();
}
7.81% (26722304/342028776)
8.05% (27535016/342028776)
8.28% (28307984/342028776)
8.5% (29086548/342028776)
8.74% (29898692/342028776)
8.98% (30704184/342028776)
9.22% (31522816/342028776)
从.Net 4.5开始，您可以使用IProgress<T>接口处理异步进度报告。您可以使用IProgress<T>编写一个下载文件的扩展方法，可以这样调用，其中HttpClient是您的porgress栏或其他UI内容的progress的实现：
IProgress<float>此扩展方法的代码如下所示。请注意，此扩展依赖于另一个扩展来处理具有进度报告的异步流复制。
// Seting up the http client used to download the data
using (var client = new HttpClient()) {
client.Timeout = TimeSpan.FromMinutes(5);
// Create a file stream to store the downloaded data.
// This really can be any type of writeable stream.
using (var file = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.None)) {
// Use the custom extension method below to download the data.
// The passed progress-instance will receive the download status updates.
await client.DownloadAsync(DownloadUrl, file, progress, cancellationToken);
}
}
通过流扩展实现真正的进度报告：
public static class HttpClientExtensions
{
public static async Task DownloadAsync(this HttpClient client, string requestUri, Stream destination, IProgress<float> progress = null, CancellationToken cancellationToken = default) {
// Get the http headers first to examine the content length
using (var response = await client.GetAsync(requestUri, HttpCompletionOption.ResponseHeadersRead)) {
var contentLength = response.Content.Headers.ContentLength;
using (var download = await response.Content.ReadAsStreamAsync()) {
// Ignore progress reporting when no progress reporter was
// passed or when the content length is unknown
if (progress == null || !contentLength.HasValue) {
await download.CopyToAsync(destination);
return;
}
// Convert absolute progress (bytes downloaded) into relative progress (0% - 100%)
var relativeProgress = new Progress<long>(totalBytes => progress.Report((float)totalBytes / contentLength.Value));
// Use extension method to report progress while downloading
await download.CopyToAsync(destination, 81920, relativeProgress, cancellationToken);
progress.Report(1);
}
}
}
}
以下代码显示了针对public static class StreamExtensions
{
public static async Task CopyToAsync(this Stream source, Stream destination, int bufferSize, IProgress<long> progress = null, CancellationToken cancellationToken = default) {
if (source == null)
throw new ArgumentNullException(nameof(source));
if (!source.CanRead)
throw new ArgumentException("Has to be readable", nameof(source));
if (destination == null)
throw new ArgumentNullException(nameof(destination));
if (!destination.CanWrite)
throw new ArgumentException("Has to be writable", nameof(destination));
if (bufferSize < 0)
throw new ArgumentOutOfRangeException(nameof(bufferSize));
var buffer = new byte[bufferSize];
long totalBytesRead = 0;
int bytesRead;
while ((bytesRead = await source.ReadAsync(buffer, 0, buffer.Length, cancellationToken).ConfigureAwait(false)) != 0) {
await destination.WriteAsync(buffer, 0, bytesRead, cancellationToken).ConfigureAwait(false);
totalBytesRead += bytesRead;
progress?.Report(totalBytesRead);
}
}
}
api必须完成的最小示例以获取下载进度。
HttpClient以上内容并未告诉您如何处理流，如何报告流程，或尝试直接解决原始问题中的代码。但是，对于希望在其代码中应用进度的未来读者来说，这个答案可能更容易理解。
与上面的@RenéSackers解决方案相同，但添加了取消下载的功能
HttpClient client = //...
// Must use ResponseHeadersRead to avoid buffering of the content
using (var response = await client.GetAsync(uri, HttpCompletionOption.ResponseHeadersRead)){
// You must use as stream to have control over buffering and number of bytes read/received
using (var stream = await response.Content.ReadAsStreamAsync())
{
// Read/process bytes from stream as appropriate
// Calculated by you based on how many bytes you have read. Likely incremented within a loop.
long bytesRecieved = //...
long? totalBytes = response.Content.Headers.ContentLength;
double? percentComplete = (double)bytesRecieved / totalBytes;
// Do what you want with `percentComplete`
}
}
嗯，你可以让另一个线程检查正在写入的流的当前大小（你也将预期的文件大小传递给它），然后相应地更新进度条。