TaskCompletionSource example.

TaskCompletionSourceBasic.cs

class Program {

    static Task<byte[]> FromWebClient(WebClient wc, Uri address) {
        var tcs = new TaskCompletionSource<byte[]>();

        wc.DownloadDataCompleted += (object sender, DownloadDataCompletedEventArgs e) => {
            if (e.Cancelled)
                tcs.SetCanceled();
            else if (e.Error != null)
                tcs.SetException(e.Error);
            else
                tcs.SetResult(e.Result);
        };
        wc.DownloadDataAsync(address);

        return tcs.Task;
    }


    static void Main(string[] args) {

        Task<int> f = Task.Factory.StartNew(() => {
            return 42;
        });

        Task<byte[]> t = FromWebClient(new WebClient(), new Uri("http://www.bing.com"));
        // t.Wait();
        t.ContinueWith(doneData => {
            var data = doneData.Result;
            var str = Encoding.UTF8.GetString(data);
            Console.WriteLine(str.Substring(0, 50));
        });
        Console.WriteLine("after task.");

        Console.ReadKey();

    }
}