C#

var list = new List<(int Key, string Value)>();
list.Add((1, "foo1"));
list.Add((1, "foo2"));
list.Add((1, "foo3"));
list.Add((1, "foo4"));
list.Add((2, "bar1"));
list.Add((2, "bar2"));
list.Add((2, "bar3"));
list.Add((2, "bar4"));
list.Add((3, "baz"));

(1, "foo2")
(1, "foo3")
(1, "foo4")
(2, "bar2")
(2, "bar3")
(2, "bar4")

private ElementHost m_elementHost;
private UserControl1 m_uc;

private void button1_Click(object sender, EventArgs e)
{   
   m_elementHost.Child = m_uc;
} 

private void button1_Click(object sender, EventArgs e)
{   
	UserControl1 uc = new UserControl1();

         uc.Show();

}