C# Definition:

[ComImport]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
[Guid("EAC04BC0-3791-11D2-BB95-0060977B464C")]
public interface IAutoComplete2 {
    [PreserveSig] int Init(
        // Handle to the window for the system edit control that is to
        // have autocompletion enabled.
        IntPtr hwndEdit,

        // Pointer to the IUnknown interface of the string list object that
        // is responsible for generating candidates for the completed
        // string. The object must expose an IEnumString interface.
        [MarshalAs(UnmanagedType.IUnknown)] object punkACL,

        // Pointer to an optional null-terminated Unicode string that gives
        // the registry path, including the value name, where the format
        // string is stored as a REG_SZ value. The autocomplete object
        // first looks for the path under HKEY_CURRENT_USER . If it fails,
        // it then tries HKEY_LOCAL_MACHINE . For a discussion of the
        // format string, see the definition of pwszQuickComplete.
        [MarshalAs(UnmanagedType.LPWStr)] string pwszRegKeyPath,

        // Pointer to an optional string that specifies the format to be
        // used if the user enters some text and presses CTRL+ENTER. Set
        // this parameter to NULL to disable quick completion. Otherwise,
        // the autocomplete object treats pwszQuickComplete as a sprintf
        // format string, and the text in the edit box as its associated
        // argument, to produce a new string. For example, set
        // pwszQuickComplete to "http://www. %s.com/". When a user enters
        // "MyURL" into the edit box and presses CTRL+ENTER, the text in
        // the edit box is updated to "http://www.MyURL.com/".
        [MarshalAs(UnmanagedType.LPWStr)] string pwszQuickComplete
    );

    // Enables or disables autocompletion.
    [PreserveSig] int Enable(bool value);

    // Sets the current autocomplete options.
    [PreserveSig] int SetOptions(AUTOCOMPLETEOPTIONS dwFlag);

    // Retrieves the current autocomplete options.
    [PreserveSig] int GetOptions(out AUTOCOMPLETEOPTIONS pdwFlag);
}

User-Defined Types:

/// <summary>
///   Specifies values used by IAutoComplete2::GetOptions and
///   "IAutoComplete2.SetOptions" for options surrounding autocomplete.
/// </summary>
/// <remarks>
///   [AUTOCOMPLETEOPTIONS Enumerated Type ()]
///   http://msdn.microsoft.com/en-us/library/bb762479.aspx
/// </remarks>
[Flags]
public enum AUTOCOMPLETEOPTIONS
{
    /// <summary>Do not autocomplete.</summary>
    ACO_NONE = 0x0000,
public enum AUTOCOMPLETEOPTIONS {
    // No autocomplete.
    ACO_NONE = 0,

    // Enable the autosuggest drop-down list.
    ACO_AUTOSUGGEST = 0x1,

    // Enable autoappend.
    ACO_AUTOAPPEND = 0x2,

    // Add a search item to the list of completed strings. Selecting this item launches a search engine.
    ACO_SEARCH = 0x4,

    // Don't match common prefixes, such as "www.", "http://", and so on.
    ACO_FILTERPREFIXES    = 0x8,        

    // Use the TAB key to select an item from the drop-down list.
    ACO_USETAB = 0x10,

    // Use the UP ARROW and DOWN ARROW keys to display the autosuggest drop-down list.
    ACO_UPDOWNKEYDROPSLIST = 0x20,

    /// <summary>Enable the autosuggest drop-down list.</summary>
    ACO_AUTOSUGGEST = 0x0001,
    // If ACO_RTLREADING is set, the text reads in the opposite direction from the text in the parent window.
    ACO_RTLREADING = 0x40
}

Notes:

None.

    /// <summary>Enable autoappend.</summary>
    ACO_AUTOAPPEND = 0x0002,

Tips & Tricks:

Please add some!

    /// <summary>Add a search item to the list of
    /// completed strings. When the user selects
    /// this item, it launches a search engine.</summary>
    ACO_SEARCH = 0x0004,

Sample Code:

static readonly Guid CLSID_AutoComplete = new Guid("{00BB2763-6A77-11D0-A535-00C04FD7D062}");

    /// <summary>Do not match common prefixes, such as
    /// "www." or "http://".</summary>
    ACO_FILTERPREFIXES = 0x0008,
private IAutoComplete2 GetAutoComplete() {
    Type CAutoComplete = Type.GetTypeFromCLSID(CLSID_AutoComplete);

    /// <summary>Use the TAB key to select an
    /// item from the drop-down list.</summary>
    ACO_USETAB = 0x0010,
    return (IAutoComplete2)Activator.CreateInstance(CAutoComplete);
}

    /// <summary>Use the UP ARROW and DOWN ARROW keys to
    /// display the autosuggest drop-down list.</summary>
    ACO_UPDOWNKEYDROPSLIST = 0x0020,

    /// <summary>Normal windows display text left-to-right
    /// (LTR). Windows can be mirrored to display languages
    /// such as Hebrew or Arabic that read right-to-left (RTL).
    /// Typically, control text is displayed in the same
    /// direction as the text in its parent window. If
    /// ACO_RTLREADING is set, the text reads in the opposite
    /// direction from the text in the parent window.</summary>
    ACO_RTLREADING = 0x0040,

Alternative Managed API:

Do you know one? Please contribute it!

    /// <summary>[Windows Vista and later]. If set, the
    /// autocompleted suggestion is treated as a phrase
    /// for search purposes. The suggestion, Microsoft
    /// Office, would be treated as "Microsoft Office"
    /// (where both Microsoft AND Office must appear in
    /// the search results).</summary>
    ACO_WORD_FILTER = 0x0080,

    /// <summary>[Windows Vista and later]. Disable prefix
    /// filtering when displaying the autosuggest dropdown.
    /// Always display all suggestions.</summary>
    ACO_NOPREFIXFILTERING = 0x0100
}

Notes:

None.

Tips & Tricks:

For an extended example see:

[CodeProject: C# does Shell, Part 4]

Sample Code:

static readonly Guid CLSID_AutoComplete = new Guid("{00BB2763-6A77-11D0-A535-00C04FD7D062}");

private IAutoComplete2 GetAutoComplete() {
    Type CAutoComplete = Type.GetTypeFromCLSID(CLSID_AutoComplete);

    return (IAutoComplete2)Activator.CreateInstance(CAutoComplete);
}

Alternative Managed API:

Do you know one? Please contribute it!

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