Updating parent process GUI on receiving Process.Exited event - WPF

Question

I am trying to launch a process within an application. The code below simply starts notepad on clicking the button of the main GUI. Now when the notepad is launched the button is disabled. I have subscribed to the Process.Exited even to receive notification when the notepad application closes. Once the notification is received I would like to re-enable the button again.

However, code crashed when I call the button1.IsEnabled = true; It seems to that Process.Exit is not a part of the main GUI thread and hence when i try to update GUI within that it crashed. Also when i am debugging I dont receive any exception saying I am trying to access main thread from outside or something.

Is there a way to notify GUI when the child process exits?

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.ComponentModel;
using System.Diagnostics;

namespace ProcessWatch
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Process pp = null;
        public MainWindow()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            pp = new Process();
            pp.EnableRaisingEvents = true;
            pp.Exited += new EventHandler(pp_Exited);
            ProcessStartInfo oStartInfo = new ProcessStartInfo();
            oStartInfo.FileName = "Notepad.exe";
            oStartInfo.UseShellExecute = false;
            pp.StartInfo = oStartInfo;
            pp.Start();
            button1.IsEnabled = false;
        }

        void pp_Exited(object sender, EventArgs e)
        {
            Process p = sender as Process;
            button1.IsEnabled = true;               
        }
    }
}

Answer 1

Try the following:

void pp_Exited(object sender, EventArgs e){ 
   Dispatcher.BeginInvoke(new Action(delegate {    
      button1.IsEnabled = true;       
   }), System.Windows.Threading.DispatcherPriority.ApplicationIdle, null);
}