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();
我如何实现进度条功能？ 也许到目前为止我可以写出写入的字节数？还是什么？
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 - 并且DownloadOperations中不存在此功能。
答案 0 :(得分：22)
最好的方法是使用Windows.Web.Http.HttpClient代替System.Net.Http.HttpClient。第一个支持进步。
但是如果出于某种原因你想坚持使用System.Net，那么你需要实现自己的进步。
移除DataWriter，移除InMemoryRandomAccessStream和将HttpCompletionOption.ResponseHeadersRead添加到GetAsync来电，以便在收到邮件后立即返回，而不是当收到整个回复时。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();
答案 1 :(得分：19)
这是一个自包含的类，它将执行下载，并根据this SO answer上 TheBlueSky 和 eriksendc this GitHub comment。
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();
}
}
用法：
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();
}
结果：
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)
答案 2 :(得分：13)
IProgress<T> 从.Net 4.5开始，您可以使用IProgress<T>界面处理异步进度报告。您可以编写一个使用HttpClient下载文件的扩展方法，可以这样调用，其中progress是您的porgress栏或其他UI内容的IProgress<float>实现：
// 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);
}
}
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。
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);
}
}
}
}
通过流扩展实现真正的进度报告：
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);
}
}
}
答案 3 :(得分：3)
以下代码显示了针对HttpClient api必须执行的操作的最小示例，以获取下载进度。
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`
}
}
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，希望在其代码中应用进展的未来读者可能更容易理解这一答案。
答案 4 :(得分：2)
与上述@RenéSackers解决方案相同，但增加了取消下载的功能
class HttpClientDownloadWithProgress : IDisposable
{
private readonly string _downloadUrl;
private readonly string _destinationFilePath;
private readonly CancellationToken? _cancellationToken;
private HttpClient _httpClient;
public delegate void ProgressChangedHandler(long? totalFileSize, long totalBytesDownloaded, double? progressPercentage);
public event ProgressChangedHandler ProgressChanged;
public HttpClientDownloadWithProgress(string downloadUrl, string destinationFilePath, CancellationToken? cancellationToken = null)
{
_downloadUrl = downloadUrl;
_destinationFilePath = destinationFilePath;
_cancellationToken = cancellationToken;
}
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
{
int bytesRead;
if (_cancellationToken.HasValue)
{
bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length, _cancellationToken.Value);
}
else
{
bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length);
}
if (bytesRead == 0)
{
isMoreToRead = false;
continue;
}
await fileStream.WriteAsync(buffer, 0, bytesRead);
totalBytesRead += bytesRead;
readCount += 1;
if (readCount % 10 == 0)
TriggerProgressChanged(totalDownloadSize, totalBytesRead);
}
while (isMoreToRead);
}
//the last progress trigger should occur after the file handle has been released or you may get file locked error
TriggerProgressChanged(totalDownloadSize, totalBytesRead);
}
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();
}
}
答案 5 :(得分：1)
RenéSackers版本非常出色，但可能会更好。具体而言，它具有由流关闭前的TriggerProgressChanged触发引起的微妙竞争条件。解决方法是在显式处理流之后触发事件。下面的版本包括上述更改，它继承自HttpClient并添加了对取消令牌的支持。
public delegate void ProgressChangedHandler(long? totalFileSize, long totalBytesDownloaded, double? progressPercentage);
public class HttpClientWithProgress : HttpClient
{
private readonly string _DownloadUrl;
private readonly string _DestinationFilePath;
public event ProgressChangedHandler ProgressChanged;
public HttpClientWithProgress(string downloadUrl, string destinationFilePath)
{
_DownloadUrl = downloadUrl;
_DestinationFilePath = destinationFilePath;
}
public async Task StartDownload()
{
using (var response = await GetAsync(_DownloadUrl, HttpCompletionOption.ResponseHeadersRead))
await DownloadFileFromHttpResponseMessage(response);
}
public async Task StartDownload(CancellationToken cancellationToken)
{
using (var response = await GetAsync(_DownloadUrl, HttpCompletionOption.ResponseHeadersRead, cancellationToken))
await DownloadFileFromHttpResponseMessage(response);
}
private async Task DownloadFileFromHttpResponseMessage(HttpResponseMessage response)
{
response.EnsureSuccessStatusCode();
long? totalBytes = response.Content.Headers.ContentLength;
using (var contentStream = await response.Content.ReadAsStreamAsync())
await ProcessContentStream(totalBytes, contentStream);
}
private async Task ProcessContentStream(long? totalDownloadSize, Stream contentStream)
{
long totalBytesRead = 0L;
long readCount = 0L;
byte[] buffer = new byte[8192];
bool isMoreToRead = true;
using (FileStream fileStream = new FileStream(_DestinationFilePath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true))
{
do
{
int bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length);
if (bytesRead == 0)
{
isMoreToRead = false;
continue;
}
await fileStream.WriteAsync(buffer, 0, bytesRead);
totalBytesRead += bytesRead;
readCount += 1;
if (readCount % 10 == 0)
TriggerProgressChanged(totalDownloadSize, totalBytesRead);
}
while (isMoreToRead);
}
TriggerProgressChanged(totalDownloadSize, totalBytesRead);
}
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);
}
}
答案 6 :(得分：0)
嗯，您可以让另一个线程检查正在写入的流的当前大小（您还将预期的文件大小传递给它），然后相应地更新进度条。
答案 7 :(得分：0)
这是 René Sackers 回答的修改版本，具有以下功能变化：
用法：
await DownloadWithProgress.ExecuteAsync(HttpClients.General, assetUrl, downloadFilePath, progressHandler, () =>
{
var requestMessage = new HttpRequestMessage(HttpMethod.Get, assetUrl);
requestMessage.Headers.Accept.TryParseAdd("application/octet-stream");
return requestMessage;
});
我想我不是唯一需要自定义标题的人，所以我想我会分享这个重写
实施：
public delegate void DownloadProgressHandler(long? totalFileSize, long totalBytesDownloaded, double? progressPercentage);
public static class DownloadWithProgress
{
public static async Task ExecuteAsync(HttpClient httpClient, string downloadPath, string destinationPath, DownloadProgressHandler progress, Func<HttpRequestMessage> requestMessageBuilder = null)
{
requestMessageBuilder ??= GetDefaultRequestBuilder(downloadPath);
var download = new HttpClientDownloadWithProgress(httpClient, destinationPath, requestMessageBuilder);
download.ProgressChanged += progress;
await download.StartDownload();
download.ProgressChanged -= progress;
}
private static Func<HttpRequestMessage> GetDefaultRequestBuilder(string downloadPath)
{
return () => new HttpRequestMessage(HttpMethod.Get, downloadPath);
}
}
internal class HttpClientDownloadWithProgress
{
private readonly HttpClient _httpClient;
private readonly string _destinationFilePath;
private readonly Func<HttpRequestMessage> _requestMessageBuilder;
private int _bufferSize = 8192;
public event DownloadProgressHandler ProgressChanged;
public HttpClientDownloadWithProgress(HttpClient httpClient, string destinationFilePath, Func<HttpRequestMessage> requestMessageBuilder)
{
_httpClient = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
_destinationFilePath = destinationFilePath ?? throw new ArgumentNullException(nameof(destinationFilePath));
_requestMessageBuilder = requestMessageBuilder ?? throw new ArgumentNullException(nameof(requestMessageBuilder));
}
public async Task StartDownload()
{
using var requestMessage = _requestMessageBuilder.Invoke();
using var response = await _httpClient.SendAsync(requestMessage, HttpCompletionOption.ResponseHeadersRead);
await DownloadAsync(response);
}
private async Task DownloadAsync(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 = ArrayPool<byte>.Shared.Rent(_bufferSize);
var isMoreToRead = true;
using (var fileStream = new FileStream(_destinationFilePath, FileMode.Create, FileAccess.Write, FileShare.None, _bufferSize, true))
{
do
{
var bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length);
if (bytesRead == 0)
{
isMoreToRead = false;
ReportProgress(totalDownloadSize, totalBytesRead);
continue;
}
await fileStream.WriteAsync(buffer, 0, bytesRead);
totalBytesRead += bytesRead;
readCount += 1;
if (readCount % 100 == 0)
ReportProgress(totalDownloadSize, totalBytesRead);
}
while (isMoreToRead);
}
ArrayPool<byte>.Shared.Return(buffer);
}
private void ReportProgress(long? totalDownloadSize, long totalBytesRead)
{
double? progressPercentage = null;
if (totalDownloadSize.HasValue)
progressPercentage = Math.Round((double)totalBytesRead / totalDownloadSize.Value * 100, 2);
ProgressChanged?.Invoke(totalDownloadSize, totalBytesRead, progressPercentage);
}
}