Execute a Method Asynchronously Using the Dispatcher Queue

   
  
<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="WPF" Width="220" Height="104" >
    <StackPanel Orientation="Vertical">
        <Button Click="StartStop_Click" Name="btnStartStop">Start</Button>
        <StackPanel Orientation="Horizontal">
            <TextBlock>Biggest Prime Found:</TextBlock>
            <TextBlock Name="txtNumber"/>
        </StackPanel>
    </StackPanel>
</Window>

//File:Window.xaml.cs

using System;
using System.Windows;
using System.Windows.Threading;


namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        private bool continueCalculating = false;

        public Window1() : base()
        {
            InitializeComponent();
        }

        private void StartStop_Click(object sender, RoutedEventArgs e)
        {
            if(continueCalculating)
            {
                continueCalculating = false;
                btnStartStop.Content = "Start";
            }
            else
            {
                continueCalculating = true;
                btnStartStop.Content = "Stop";
                this.Dispatcher.BeginInvoke(DispatcherPriority.Normal,new Action<int>(UpdateNumber), 3);
            }
        }

        public void UpdateNumber(int current)
        {
            txtNumber.Text = current.ToString();
            if(continueCalculating)
            {
                this.Dispatcher.BeginInvoke(DispatcherPriority.SystemIdle,new Action<int>(UpdateNumber), current + 2);
            }
        }
    }

}