HttpClient? ???? ??? ????? ? ??? ??? ??

??

? ????? HttpClient? ???? ??? ????? ? ??? ???? ???? ??? ?????. ??? ?? ???? ?? DownloadOperation? ??? ? ???? ?? ?? ??? ?????.

IProgress ??

.Net 4.5?? IProgress? ???? ?? ??? ?????. ?? ????? ?? HttpClient? ???? ??? ?? ??? ????.

// HttpClient ?? (var client = new HttpClient()) {

// 帶進(jìn)度報(bào)告的文件下載
await client.DownloadAsync(DownloadUrl, file, progress, cancellationToken);

}

?? ??? ??

DownloadAsync ?? ??? ??? ?? ??? ?? ??? ??? ?? ?? ?? ??? ?? ????.

public static async Task DownloadAsync(this HttpClient client, string requestUri, Stream destination, IProgress<float> progress = null, CancellationToken cancellationToken = default) {

    // 獲取內(nèi)容長度的標(biāo)頭
    using (var response = await client.GetAsync(requestUri, HttpCompletionOption.ResponseHeadersRead)) {
        // 如果不支持，則忽略進(jìn)度報(bào)告
        if (progress == null || !response.Content.Headers.ContentLength.HasValue) {
            await response.Content.ReadAsStreamAsync(cancellationToken).CopyToAsync(destination);
            return;
        }

        // 計(jì)算相對(duì)進(jìn)度
        var relativeProgress = new Progress<long>(totalBytes => progress.Report((float)totalBytes / response.Content.Headers.ContentLength.Value));
        // 帶進(jìn)度報(bào)告的下載
        await response.Content.ReadAsStreamAsync().CopyToAsync(destination, 81920, relativeProgress, cancellationToken);
        progress.Report(1);
    }
}

public static async Task CopyToAsync(this Stream source, Stream destination, int bufferSize, IProgress<long> progress = null, CancellationToken cancellationToken = default) {

    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);
    }
}

<code>

通過以上代碼，開發(fā)者可以輕松地在使用HttpClient下載文件的同時(shí)，實(shí)現(xiàn)進(jìn)度條功能，提升用戶體驗(yàn)。  需要注意的是，`CopyToAsync` 方法中的 `bufferSize` 參數(shù)可以根據(jù)實(shí)際情況調(diào)整，以平衡性能和內(nèi)存消耗。</code>

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