how to set horizontal scroll in dropdownlist ?

private void DisplayHScroll()
{
   // Make no partial items are displayed vertically.
   listBox1.IntegralHeight = true;
 
   // Add items that are wide to the ListBox.
   for (int x = 0; x < 10; x++)
   {
      listBox1.Items.Add("Item  " + x.ToString() + " is a very large value that requires scroll bars");
   }
 
   // Display a horizontal scroll bar.
   listBox1.HorizontalScrollbar = true;
 
   // Create a Graphics object to use when determining the size of the largest item in the ListBox.
   Graphics g = listBox1.CreateGraphics();
 
   // Determine the size for HorizontalExtent using the MeasureString method using the last item in the list.
   int hzSize = (int) g.MeasureString(listBox1.Items[listBox1.Items.Count -1].ToString(),listBox1.Font).Width;
   // Set the HorizontalExtent property.
   listBox1.HorizontalExtent = hzSize;
}