Implement WebClient’s asynchronous download with cancellation capability


When I wrote my article regarding use of the BackgroundWorker to keep the UI responsive, I used the WebClient’s DownloadString method as an example of a long-running process. I used this as an example in explaining how to use the BackgroundWorker, which simply allows for thread-blocking code to be run in a separate thread.

As it turns out, this is a terrible idea. Not the whole thread-blocking code in a separate thread, but the use of a WebClient in a BackgroundWorker. You see, the WebClient class implements a DownloadStringAsync() method. This allows the calling code to continue to run, and the asynchronous process will eventually return a string. But since it’s asynchronous, our UI thread will never get blocked by a long-running process. And since it too supports asynchronous cancellation, there’s no reason to embed it inside a BackgroundWorker. Continue reading