WPF

using System;
using System.Timers;
using System.Windows;
using System.Windows.Controls;

namespace WpfApplication1
{
    public partial class Timeline : UserControl
    {
        Timer timer = null;

        public string CurrentTime
        {
            get { return (string)GetValue(CurrentTimeProperty); }
            set { SetValue(CurrentTimeProperty, value); }
        }

        public static readonly DependencyProperty CurrentTimeProperty =
            DependencyProperty.Register("CurrentTime", typeof(string), typeof(Timeline), new PropertyMetadata(""));

        public Timeline()
        {
            InitializeComponent();

            setup();
        }

        private void setup()
        {
            timer = new Timer();
            timer.Elapsed += timer_Elapsed;
            timer.Interval = 1000;
            timer.Enabled = true;
        }

        private void timer_Elapsed(object sender, ElapsedEventArgs e)
        {
            CurrentTime = DateTime.Now.TimeOfDay.ToString();
        }
    }
}

The calling thread cannot access this object because a different thread owns it.

public List<Person> People = new List<Person>();

People.Add(new Person { Id = 0, Name = "Joe" });
People.Add(new Person { Id = 1, Name = "Pete" });
People.Add(new Person { Id = 2, Name = "Sam" });

System.Windows.Controls.DataGridComboBoxColumn comboCol = new System.Windows.Controls.DataGridComboBoxColumn();
comboCol.Header = "People";
comboCol.ItemsSource = People;
comboCol.DisplayMemberPath = "Name";
comboCol.SelectedValuePath = "Id";
this.taskGrid.Columns.Add(comboCol);