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(jìn)度報(bào)告器或內(nèi)容長度未知時(shí)忽略進(jìn)度報(bào)告
            if (progress == null || !contentLength.HasValue)
            {
                await download.CopyToAsync(destination);
                return;
            }

            // 將絕對(duì)進(jìn)度（已下載字節(jié)數(shù)）轉(zhuǎn)換為相對(duì)進(jìn)度（0% - 100%）
            var relativeProgress = new Progress<long>(totalBytes => progress.Report((float)totalBytes / contentLength.Value));
            // 使用擴(kuò)展方法在下載時(shí)報(bào)告進(jìn)度
            await download.CopyToAsync(destination, 81920, relativeProgress, cancellationToken);
            progress.Report(1); // 報(bào)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? ???? ?? ???? ??? ?? ??? ??? ??? ?? ??? ? ????.

? ??? .NET?? HttpClient? ???? ??? ???? ???? ??? ??????? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!