How to Implement a Progress Bar with HttpClient During File Downloads?
Jan 12, 2025 pm 06:46 PMImplement progress bar when downloading files using HttpClient
Introduction
This article describes how to use HttpClient to implement a progress bar when downloading files. Since DownloadOperation cannot be used due to certificate handling limitations, another approach is required.
Use IProgress
Starting in .Net 4.5, IProgress
// Set up HttpClient using (var client = new HttpClient()) {
// 帶進度報告的文件下載 await client.DownloadAsync(DownloadUrl, file, progress, cancellationToken);
}
Extension method implementation
The DownloadAsync extension method depends on another extension method for stream replication with progress reporting:
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,則忽略進度報告 if (progress == null || !response.Content.Headers.ContentLength.HasValue) { await response.Content.ReadAsStreamAsync(cancellationToken).CopyToAsync(destination); return; } // 計算相對進度 var relativeProgress = new Progress<long>(totalBytes => progress.Report((float)totalBytes / response.Content.Headers.ContentLength.Value)); // 帶進度報告的下載 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,實現(xiàn)進度條功能,提升用戶體驗。 需要注意的是,`CopyToAsync` 方法中的 `bufferSize` 參數(shù)可以根據(jù)實際情況調(diào)整,以平衡性能和內(nèi)存消耗。</code>
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