Check Whether You Are Running on the UI Thread

   
  

<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" Height="120" Width="364">
    <StackPanel>
        <Button Click="ButtonTrue_Click">UI Thread</Button>
        <Button Click="ButtonFalse_Click">Non-UI Thread</Button>
        <TextBlock x:Name="txtResult"/>
    </StackPanel>
</Window>
//File:Window.xaml.cs
using System.Windows;
using System.Windows.Threading;

namespace WpfApplication1
{
    public partial class Window1 : Window
    {
        private delegate void CheckAccessDelegate();
        private delegate void SetResultTextDelegate(string result);
        public Window1()
        {
            InitializeComponent();
        }

        private void ButtonTrue_Click(object sender, RoutedEventArgs e)
        {
            CheckAccess();
        }

        private void ButtonFalse_Click(object sender, RoutedEventArgs e)
        {
            CheckAccessDelegate del = new CheckAccessDelegate(CheckAccess);
            del.BeginInvoke(null, null);
        }

        private void CheckAccess()
        {
            if(txtResult.Dispatcher.CheckAccess())
            {
                txtResult.Text = "True";
            }else{
                txtResult.Dispatcher.BeginInvoke(DispatcherPriority.Normal,new SetResultTextDelegate(SetResultText),"False");
            }
        }

        private void SetResultText(string result)
        {
            txtResult.Text = result;
        }
    }
}