System.Windows.Forms.ContextMenu contextMenu1; 
contextMenu1 = new System.Windows.Forms.ContextMenu(); 
System.Windows.Forms.MenuItem menuItem1; 
menuItem1 = new System.Windows.Forms.MenuItem(); 
System.Windows.Forms.MenuItem menuItem2; 
menuItem2 = new System.Windows.Forms.MenuItem(); 
System.Windows.Forms.MenuItem menuItem3; 
menuItem3 = new System.Windows.Forms.MenuItem(); 

contextMenu1.MenuItems.AddRange(new System.Windows.Forms.MenuItem[] {menuItem1, menuItem2, menuItem3}); 
menuItem1.Index = 0; 
menuItem1.Text = "MenuItem1"; 
menuItem2.Index = 1; 
menuItem2.Text = "MenuItem2"; 
menuItem3.Index = 2; 
menuItem3.Text = "MenuItem3"; 

textBox1.ContextMenu = contextMenu1;