How Can I Implement Progress Notification During File Downloads with HttpClient in .NET 4.5?

Use .NET 4.5 HttpClient to implement file download progress notification

In .NET 4.5, the IProgress<T> interface provides a way to efficiently handle progress reporting for asynchronous operations. This allows you to implement a progress bar or other UI element to inform the user of the download status.

Download extension method with progress report

In order to adapt to the file download scenario, you can use the custom DownloadAsync method to extend the HttpClient class, which contains IProgress<T>:

<code class="language-csharp">public static class HttpClientExtensions
{
    public static async Task DownloadAsync(this HttpClient client, string requestUri, Stream destination, IProgress<float> progress = null, CancellationToken cancellationToken = default)
    {
        // ... 实现细节 ...
    }
}</code>

Implementation details

Extension methods depend on:

1. Get HTTP header information to determine content length to calculate progress.
2. Use the asynchronous stream replication extension method with progress reporting functionality.

Stream extension method for progress monitoring

Progress is tracked by updating the incoming IProgress<long>. This stream-copying extension method reports progress in the download progress:

<code class="language-csharp">public static class StreamExtensions
{
    public static async Task CopyToAsync(this Stream source, Stream destination, int bufferSize, IProgress<long> progress = null, CancellationToken cancellationToken = default)
    {
        // ... 实现细节 ...
    }
}</code>

Usage examples

You can use this extension method as follows:

<code class="language-csharp">// 创建HTTP客户端
using (var client = new HttpClient())
{
    // 创建用于保存下载数据的文件
    using (var file = new FileStream("download.dat", FileMode.Create))
    {
        // 注册进度回调
        var progress = new Progress<float>(p => Console.WriteLine($"Progress: {p * 100}%"));

        // 使用进度报告下载数据
        await client.DownloadAsync(downloadUrl, file, progress);
    }
}</code>

This extension allows you to implement a progress bar when downloading files over HTTP while ensuring that data requested from the server requires a certificate, while DownloadOperations this feature is not supported.

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