HttpClient? ???? .NET?? ??? ??? ??
.NET 4.5? ??? IProgress<T> ?????? ???? ??? ??? ??? ??? ? ???? HttpClient? ???? ??? ?????? ?? ??? ??? ??? ??? ? ????.
IProgress<T>
? ??? ?? ??
DownloadAsync ??? ????? ????? HttpClient? IProgress<float> ??? ?? ?? ???? ????. ? ??? ???? ??? ??? ????? UI? ???????.
public static async Task DownloadAsync(this HttpClient client, string requestUri, Stream destination, IProgress<float> progress = null, CancellationToken cancellationToken = default)
{
// 首先獲取 http 頭信息以檢查內(nèi)容長度
using (var response = await client.GetAsync(requestUri, HttpCompletionOption.ResponseHeadersRead))
{
var contentLength = response.Content.Headers.ContentLength;
using (var download = await response.Content.ReadAsStreamAsync(cancellationToken))
{
// 未傳遞進度報告器或內(nèi)容長度未知時忽略進度報告
if (progress == null || !contentLength.HasValue)
{
await download.CopyToAsync(destination);
return;
}
// 將絕對進度（已下載字節(jié)數(shù)）轉(zhuǎn)換為相對進度（0% - 100%）
var relativeProgress = new Progress<long>(totalBytes => progress.Report((float)totalBytes / contentLength.Value));
// 使用擴展方法在下載時報告進度
await download.CopyToAsync(destination, 81920, relativeProgress, cancellationToken);
progress.Report(1); // 報告100%完成
}
}
}
? ???? progress.Report() ???? ?? ???? ???(???)? IProgress<float> ??? ???? ?? ?? ??? ????? ?? UI ??? ????? ? ??? ???.
?? ?? ??? ?? ??? ??
???? ?? ???? ??? ? ?? ?? ?? ??? ????? Stream ???? ?? ?? ??? ??? ?????.
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("必須可讀", nameof(source));
if (destination == null)
throw new ArgumentNullException(nameof(destination));
if (!destination.CanWrite)
throw new ArgumentException("必須可寫", 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);
}
}
? ?? ???? ?? ???? ??? ??? ?? ?????? ??? IProgress<long> ??? ???? ?? ??? ?????.
??? ?? ??? ???? HttpClient? ???? ?? ???? ??? ?? ??? ??? ??? ?? ??? ? ????.
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