C# 5.0 vNext - New Asynchronous Pattern

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Net;
using System.Xml.Linq;
using System.Threading.Tasks;
using System.Threading;

namespace WpfAsynchrony
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        const string Feed = "http://www.codeproject.com/webservices/articlerss.aspx?cat={0}";
        public MainWindow()
        {
            InitializeComponent();
        }

        private void btnSync_Click(object sender, RoutedEventArgs e)
        {
            this.SynchronousCallServer();
        }

        private void btnaSyncPrev_Click(object sender, RoutedEventArgs e)
        {
            StringBuilder builder = new StringBuilder();
            this.AsynchronousCallServerTraditional(builder, 2);
        }

        public void AsynchronousCallServerTraditional(StringBuilder builder, int i)
        {
            if (i > 10)
            {
                MessageBox.Show(string.Format("Downloaded Successfully!!! Total Size : {0} chars.", builder.Length));
                return;
            }
            this.tbStatus.Text = string.Format("Calling Server [{0}]..... ", i);
            WebClient client = new WebClient();

            client.DownloadStringCompleted += (o, e) =>
            {
                builder.Append(e.Result);
                this.AsynchronousCallServerTraditional(builder, i + 1);
            };

            string currentCall = string.Format(Feed, i);
            client.DownloadStringAsync(new Uri(currentCall), null);

        }

        public void SynchronousCallServer()
        {
            WebClient client = new WebClient();

            StringBuilder builder = new StringBuilder();

            for (int i = 2; i <= 10; i++)
            {
                this.tbStatus.Text = string.Format("Calling Server [{0}]..... ", i);
                string currentCall = string.Format(Feed, i);
                string rss = client.DownloadString(new Uri(currentCall));

                builder.Append(rss);
            }

            MessageBox.Show(string.Format("Downloaded Successfully!!! Total Size : {0} chars.", builder.Length));
        }

        private async void btnaSyncPres_Click(object sender, RoutedEventArgs e)
        {
            await this.AsynchronousCallServerMordernAsync();
        }
        public async Task AsynchronousCallServerMordernAsync()
        {
            WebClient client = new WebClient();

            StringBuilder builder = new StringBuilder();

            for (int i = 2; i <= 10; i++)
            {
                try
                {
                    this.tbStatus.Text = string.Format("Calling Server [{0}]..... ", i);
                    string currentCall = string.Format(Feed, i);
                    string rss = await client.DownloadStringTaskAsync(new Uri(currentCall));

                    builder.Append(rss);
                }
                catch (Exception ex)
                {
                    this.tbStatus.Text = string.Format("Error Occurred -- {0} for call :{1}, Trying next", ex.Message, i);
                }

                MessageBox.Show(string.Format("Downloaded Successfully!!! Total Size : {0} chars.", builder.Length));
            }

        }

        private async void btnaSyncPresParallel_Click(object sender, RoutedEventArgs e)
        {
            await this.AsynchronousCallServerMordernParallelAsync();
        }

        public async Task AsynchronousCallServerMordernParallelAsync()
        {

            List<Task<string>> lstTasks = new List<Task<string>>();

            StringBuilder builder = new StringBuilder();

            for (int i = 2; i <= 10; i++)
            {
                using (WebClient client = new WebClient())
                {
                    try
                    {
                        this.tbStatus.Text = string.Format("Calling Server [{0}]..... ", i);
                        string currentCall = string.Format(Feed, i);
                        Task<string> task = client.DownloadStringTaskAsync(new Uri(currentCall));
                        lstTasks.Add(task);

                    }
                    catch (Exception ex)
                    {
                        this.tbStatus.Text = string.Format("Error Occurred -- {0} for call :{1}, Trying next", ex.Message, i);
                    }
                }


            }
            string[] rss = await TaskEx.WhenAll<string>(lstTasks);
            foreach (string s in rss)
                builder.Append(s);

            MessageBox.Show(string.Format("Downloaded Successfully!!! Total Size : {0} chars.", builder.Length));
        }

        private async void btnGoCPUBound_Click(object sender, RoutedEventArgs e)
        {
            await new SynchronizationContext().SwitchTo();  //Switch to net Thread from ThreadPool

            long result = this.DoCpuIntensiveWork(); //Very CPU intensive

            await Application.Current.Dispatcher.SwitchTo();

            MessageBox.Show(string.Format("Largest Prime number : {0}", result));

        }

        public long DoCpuIntensiveWork()
        {
            long i = 2, j, rem, result = 0;
            while (i <= long.MaxValue)
            {
                for (j = 2; j < i; j++)
                {
                    rem = i % j;
                    if (rem == 0)
                        break;
                }
                if (i == j)
                    result = i;
                i++;
            }
            return result;
        }

    }
}