I set the Listbox's BorderStyle = BorderStyle.None, but I want to draw a simple border line around.

Code:
public partial class DropDownListBox : ListBox
    {
		public DropDownListBox()
		{
			//SetStyle(ControlStyles.UserPaint, true);
			BorderStyle = BorderStyle.None;
		}

		protected override void OnPaintBackground(PaintEventArgs e)
		{			
			if (BorderStyle == BorderStyle.None)
			{
				e.Graphics.DrawRectangle(SystemPens.ControlDarkDark, 0, 0, base.Width - 1, base.Height - 1);
			}			
		}		
	}
SetStyle(ControlStyles.UserPaint, true) will cause all items aren't drawn.