Calling Long Running Methods Asynchronously

When you are able to call an async method, do it using async and await or by making your method return a Task:

public async Task<string> RequestData(Uri uri)

{

    WebClient webClient = new WebClient();

    return await webClient.DownloadStringTaskAsync(uri);

} // Rely on underlying Tasks whenever possible.

public Task<string> RequestDataAsync(Uri uri)

{

    WebClient webClient = new WebClient();

    return webClient.DownloadStringTaskAsync(uri);

} // Rely on underlying Tasks whenever possible.

Dealing with synchronous calls

When the method you are calling is not asynchronous, wrap the method in a task delegate:

 

public Task<string> RequestDataAsync(Uri uri)

{

    return Task.Run<string>(

        () =>

        {

            WebClient webClient = new WebClient();

            return webClient.DownloadString(uri);

        });

} // Create Tasks when you have no other choice.

Capturing Exceptions

Getting a little more advanced, what if you might need to capture exceptions from a long running method? Use the following pattern:
 

public Task<string> RequestDataAsync(Uri uri)

{

    var tcs = new TaskCompletionSource<string>();

    WebClient webClient = new WebClient();

    webClient.DownloadStringCompleted +=

        (_, args) =>

        {

            tcs.SetResult(args.Result);

        };

    webClient.DownloadStringAsync(uri);

    return tcs.Task;

} // Example of wrapping Async/Completed.

More info

Async'ing Your Way to a Successful App with .NET
http://channel9.msdn.com/Events/Build/2013/3-301

Creating Async Libraries That Are Modular, Reusable and Fast, in Microsoft Visual C# and Visual Basic
http://channel9.msdn.com/Events/TechEd/Europe/2013/DEV-B318