Use the ComboBox.AutoCompleteCustomSource, ComboBox.AutoCompleteMode, and ComboBox.AutoCompleteSource properties to create a System.Windows.Forms.ComboBox that automatically completes input strings by comparing the prefix being entered to the prefixes of all strings in a maintained source. This is useful for System.Windows.Forms.ComboBox controls in which URLs, addresses, file names, or commands will be frequently entered. If there are duplicate entries in the maintained source, automatic completion behaves unpredictably.

If you set System.Windows.Forms.ComboBoxStyle to ComboBoxStyle.DropDownList, the list displays only if ComboBox.AutoCompleteMode is AutoCompleteMode.Suggest or AutoCompleteMode.SuggestAppend.

The use of the ComboBox.AutoCompleteCustomSource property is optional, but you must set the ComboBox.AutoCompleteSource property to AutoCompleteSource.CustomSource in order to use ComboBox.AutoCompleteCustomSource.

You must use the ComboBox.AutoCompleteMode and ComboBox.AutoCompleteSource properties together.

With ComboBox.AutoCompleteMode set to AutoCompleteMode.SuggestAppend and ComboBox.AutoCompleteSource set to AutoCompleteSource.ListItems, the behavior is as follows:

• If the list of strings is empty, pressing the BACKSPACE or DELETE key does nothing.

• If the BACKSPACE key is pressed in less than one second, the previous item is selected, or nothing is selected if the list of string is empty.

• If the BACKSPACE key is pressed in more than one second, the first item is selected.

• If the DELETE key is pressed, the first item is selected.