create a C# context menu from code

I try the one of your approach,
it works well in my computer. Below is my code:

 public void AddContextMenu()

  {

   ContextMenu mnuContextMenu = new ContextMenu();

   mnuContextMenu.MenuItems.Add("&Red LED", new EventHandler(SetDisplayRed));

   mnuContextMenu.MenuItems.Add("&Blue LED", new EventHandler(SetDisplayBlue));

   mnuContextMenu.MenuItems.Add("&LCD", new EventHandler(SetDisplayLCD));

   textBox1.ContextMenu = mnuContextMenu;

   this.ContextMenu = mnuContextMenu;

  }

private void SetDisplayRed(object sender, EventArgs e)

  {
textBox1.BackColor = Color.Maroon;

   textBox1.ForeColor = Color.OrangeRed;

  }
private void SetDisplayBlue(object sender, EventArgs e)

  {

   textBox1.BackColor = Color.Red;

   textBox1.ForeColor = Color.Gray;

  }
private void SetDisplayLCD(object sender, EventArgs e)

  {

   textBox1.BackColor = Color.Beige;

   textBox1.ForeColor = Color.Blue;

  }

>When I right-click on the textbox I get a menu with
Undo/Cut/Copy/Paste/Select All.  And when I right-click on the form I get
nothing

Have you already added your "AddContextMenu()" method into the
contruction method of your mainform?

public MainForm()

  {

   InitializeComponent();

AddContextMenu();

  }

create a C# context menu from code