This documentation is archived and is not being maintained.

ComboBox.AutoCompleteSource Property

Note: This property is new in the .NET Framework version 2.0.

Gets or sets a value specifying the source of complete strings used for automatic completion.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in

public AutoCompleteSource AutoCompleteSource { get; set; }
/** @property */
public AutoCompleteSource get_AutoCompleteSource ()

/** @property */
public void set_AutoCompleteSource (AutoCompleteSource value)

public function get AutoCompleteSource () : AutoCompleteSource

public function set AutoCompleteSource (value : AutoCompleteSource)

Property Value

One of the values of AutoCompleteSource. The options are AllSystemSources, AllUrl, FileSystem, HistoryList, RecentlyUsedList, CustomSource, and None. The default is None.

Exception typeCondition


The specified value is not one of the values of AutoCompleteSource.

Use the AutoCompleteCustomSource, AutoCompleteMode, and AutoCompleteSource properties to create a 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 ComboBox controls in which URLs, addresses, file names, or commands will be frequently entered.

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

You must use the AutoCompleteMode and AutoCompleteSource properties together.

With AutoCompleteMode set to SuggestAppend and AutoCompleteSource set to 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.


The operating system might limit the number of custom strings that it can display at once. For strings that contain a forward slash (/) or backward slash (\), automatic completion appends all characters only up to and including the slash.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0