C# webclient.downloaddatacompleted + new

A classic!

WebClient.DownloadDataCompleted is an event that is raised when the download operation is completed. It's a part of the WebClient class in C#.

Here's an example of how you can use it:

using System;
using System.Net;

// Create a new WebClient instance
WebClient webClient = new WebClient();

// Set the event handler for the DownloadDataCompleted event
webClient.DownloadDataCompleted += new DownloadDataCompletedEventHandler(DownloadDataCompletedHandler);

// Download the data
webClient.DownloadData("https://example.com/data");

// Event handler method
void DownloadDataCompletedHandler(object sender, DownloadDataCompletedEventArgs e)
{
    // Check if the download was successful
    if (e.Error == null)
    {
        // Get the downloaded data
        byte[] data = e.Result;

        // Process the data
        Console.WriteLine("Download completed successfully!");
    }
    else
    {
        // Handle the error
        Console.WriteLine("Error downloading data: " + e.Error.Message);
    }
}

In this example, we create a new WebClient instance and set the event handler for the DownloadDataCompleted event using the += operator. We then call the DownloadData method to start the download.

When the download is completed, the DownloadDataCompleted event is raised, and the event handler method DownloadDataCompletedHandler is called. In this method, we check if the download was successful by checking the Error property of the DownloadDataCompletedEventArgs object. If the download was successful, we get the downloaded data from the Result property and process it. If there was an error, we handle it accordingly.

Note that the DownloadDataCompleted event is raised on a background thread, so you should use the SynchronizationContext class or the Invoke method to marshal the event handler method back to the UI thread if you need to update the UI.