How to Add a Progress Bar to an HttpClient File Downloader?

Enhance Your HttpClient File Downloader with a Progress Bar

This guide demonstrates how to add a progress bar to a file downloader built using HttpClient, addressing scenarios where DownloadOperations aren't feasible due to server certificate constraints.

Leveraging IProgress for Asynchronous Progress Reporting

.NET 4.5 and later versions offer the IProgress<T> interface, ideal for asynchronous progress updates. Integrating IProgress<T> provides real-time feedback on download progress.

An Extension Method for Seamless Integration

To easily incorporate IProgress<T>, we'll create an extension method for HttpClient, allowing for this concise syntax:

<code class="language-csharp">await client.DownloadAsync(DownloadUrl, file, progress, cancellationToken);</code>

Detailed Implementation Steps

The extension method will perform these key actions:

1. Obtain Content Length: First, it retrieves HTTP headers to get the total file size.
2. Asynchronous Stream Reading: HttpClient.ReadAsStreamAsync() is used for efficient asynchronous stream reading.
3. Progress Reporting with IProgress<float>: If an IProgress<float> instance is supplied, the method uses StreamExtensions.CopyToAsync() to manage progress updates. These updates reflect the increasing number of downloaded bytes.
4. Calculate Relative Progress: The downloaded byte count is converted into a percentage for display in the progress bar.
5. Efficient Stream Copying and Reporting: StreamExtensions.CopyToAsync() handles copying the data and simultaneously reports progress via IProgress<long>.

By using IProgress<T>, you can seamlessly integrate progress information into your progress bar or other UI elements, significantly improving the user experience during file downloads.

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