Update UI on thread task complete giving error.

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WPF

threads

Dear Expert,
I'm writing an application, where I'm calling a method in a new thread. In the method i'm doing some task. On completion of task i'm sending an event to UI (update UI control). But while updating UI control, i'm getting below exception "The calling thread cannot access this object because a different thread owns it.;"

In my UI control I've two button , button1 and button2 and a treeview treeView1. On clicking button1 i'm calling the thread method. Below is my code. Please let me know what is the wrong I'm doing in my code.

Mainwindow.cs

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.Threading;

namespace AddDelete
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Thread      thread              = null;
        ThClass     objThClass          = null;

        public MainWindow()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            for (int i = 1; i <= 10; ++i)
            {
                treeView1.Items.Add(i.ToString());
            }

            objThClass = new ThClass();

            if(null == thread)
                thread = new Thread(new ThreadStart(objThClass.TestMethode));

            thread.Start();

            objThClass.Changed += TempHandler;
        }

        private void button2_Click(object sender, RoutedEventArgs e)
        {
            treeView1.Items.Clear();
        }

        public void TempHandler(object sender, EventArgs e)
        {
            try
            {
                //treeView1.Items.Clear();

                treeView1.Items.Add("Temp1");
                
                thread.Abort();
                thread = null;
            }
            catch (Exception exp)
            {
                Console.WriteLine(exp);
            }
        }
    }
}

ThClass.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Threading;

namespace AddDelete
{
    public delegate void ChangedEventHandler(object sender, EventArgs e);

    class ThClass
    {
        public event ChangedEventHandler Changed;

        public void TestMethode()
        {
            // Do some task (DB operation)
            // On task complete
            Changed(this, null);
        }
    }
}

Thank you all.