The preferred way to add items to the ComboBox is to use the AddRange method of the ComboBox.ObjectCollection class (through the Items property of the ComboBox). This enables you to add an array of items to the list at one time. However, if you want to add items one at a time using the Add method of the ComboBox.ObjectCollection class, you can use the BeginUpdate method to prevent the control from repainting the ComboBox each time an item is added to the list. Once you have completed the task of adding items to the list, call the EndUpdate method to enable the ComboBox to repaint. This way of adding items can prevent flickered drawing of the ComboBox when a large number of items are being added to the list.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)