You can use IAutoComplete2 to accomplish this task.
Check out this sample code (adapted for TButtonedEdit and Delphi XE2) based on this answer ( Automatically add / end from text file to delphi edit box ) from Ken White
uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ExtCtrls, Winapi.ActiveX, Winapi.ShlObj, Vcl.Mask, Vcl.ImgList; type IACList = interface(IUnknown) ['{77A130B0-94FD-11D0-A544-00C04FD7d062}'] function Expand(pszExpand : POLESTR) : HResult; stdcall; end; const //options for IACList2 ACLO_NONE = 0; // don't enumerate anything ACLO_CURRENTDIR = 1; // enumerate current directory ACLO_MYCOMPUTER = 2; // enumerate MyComputer ACLO_DESKTOP = 4; // enumerate Desktop Folder ACLO_FAVORITES = 8; // enumerate Favorites Folder ACLO_FILESYSONLY = 16; // enumerate only the file system type IACList2 = interface(IACList) ['{470141a0-5186-11d2-bbb6-0060977b464c}'] function SetOptions(dwFlag: DWORD): HResult; stdcall; function GetOptions(var pdwFlag: DWORD): HResult; stdcall; end; IAutoComplete = interface(IUnknown) ['{00bb2762-6a77-11d0-a535-00c04fd7d062}'] function Init(hwndEdit: HWND; const punkACL: IUnknown; pwszRegKeyPath, pwszQuickComplete: POLESTR): HResult; stdcall; function Enable(fEnable: BOOL): HResult; stdcall; end; const //options for IAutoComplete2 ACO_NONE = 0; ACO_AUTOSUGGEST = $1; ACO_AUTOAPPEND = $2; ACO_SEARCH = $4; ACO_FILTERPREFIXES = $8; ACO_USETAB = $10; ACO_UPDOWNKEYDROPSLIST = $20; ACO_RTLREADING = $40; type IAutoComplete2 = interface(IAutoComplete) ['{EAC04BC0-3791-11d2-BB95-0060977B464C}'] function SetOptions(dwFlag: DWORD): HResult; stdcall; function GetOptions(out pdwFlag: DWORD): HResult; stdcall; end; TEnumString = class(TInterfacedObject, IEnumString) private type TPointerList = array[0..0] of Pointer; //avoid bug of Classes.pas declaration TPointerList = array of Pointer; var FStrings: TStringList; FCurrIndex: integer; public //IEnumString function Next(celt: Longint; out elt; pceltFetched: PLongint): HResult; stdcall; function Skip(celt: Longint): HResult; stdcall; function Reset: HResult; stdcall; function Clone(out enm: IEnumString): HResult; stdcall; //VCL constructor Create; destructor Destroy;override; end; TACOption = (acAutoAppend, acAutoSuggest, acUseArrowKey); TACOptions = set of TACOption; TACSource = (acsList, acsHistory, acsMRU, acsShell); TButtonedEdit = class(Vcl.ExtCtrls.TButtonedEdit) private FACList: TEnumString; FAutoComplete: IAutoComplete; FACEnabled: boolean; FACOptions: TACOptions; FACSource: TACSource; function GetACStrings: TStringList; procedure SetACEnabled(const Value: boolean); procedure SetACOptions(const Value: TACOptions); procedure SetACSource(const Value: TACSource); procedure SetACStrings(const Value: TStringList); protected procedure CreateWnd; override; procedure DestroyWnd; override; public constructor Create(AOwner: TComponent); override; destructor Destroy; override; published property ACEnabled: boolean read FACEnabled write SetACEnabled; property ACOptions: TACOptions read FACOptions write SetACOptions; property ACSource: TACSource read FACSource write SetACSource; property ACStrings: TStringList read GetACStrings write SetACStrings; end; TForm1 = class(TForm) ButtonedEdit1: TButtonedEdit; ImageList1: TImageList; procedure FormCreate(Sender: TObject); private { Private declarations } public { Public declarations } end; var Form1: TForm5; implementation {$R *.dfm} uses System.Win.ComObj; procedure TForm1.FormCreate(Sender: TObject); begin ButtonedEdit1.ACEnabled:=True; ButtonedEdit1.ACOptions:=[acAutoAppend, acAutoSuggest, acUseArrowKey]; ButtonedEdit1.ACSource:=acsList; ButtonedEdit1.ACStrings.Add('string 1'); ButtonedEdit1.ACStrings.Add('string 2'); ButtonedEdit1.ACStrings.Add('string 3'); ButtonedEdit1.ACStrings.Add('string 4'); end; { TEnumString } function TEnumString.Clone(out enm: IEnumString): HResult; begin Result := E_NOTIMPL; Pointer(enm) := nil; end; constructor TEnumString.Create; begin inherited Create; FStrings := TStringList.Create; FCurrIndex := 0; end; destructor TEnumString.Destroy; begin FStrings.Free; inherited; end; function TEnumString.Next(celt: Integer; out elt; pceltFetched: PLongint): HResult; var I: Integer; wStr: WideString; begin I := 0; while (I < celt) and (FCurrIndex < FStrings.Count) do begin wStr := FStrings[FCurrIndex]; TPointerList(elt)[I] := CoTaskMemAlloc(2 * (Length(wStr) + 1)); StringToWideChar(wStr, TPointerList(elt)[I], 2 * (Length(wStr) + 1)); Inc(I); Inc(FCurrIndex); end; if pceltFetched <> nil then pceltFetched^ := I; if I = celt then Result := S_OK else Result := S_FALSE; end; function TEnumString.Reset: HResult; begin FCurrIndex := 0; Result := S_OK; end; function TEnumString.Skip(celt: Integer): HResult; begin if (FCurrIndex + celt) <= FStrings.Count then begin Inc(FCurrIndex, celt); Result := S_OK; end else begin FCurrIndex := FStrings.Count; Result := S_FALSE; end; end; { TACEdit } constructor TButtonedEdit.Create(AOwner: TComponent); begin inherited; FACList := TEnumString.Create; FACEnabled := True; FACOptions := [acAutoAppend, acAutoSuggest, acUseArrowKey]; end; procedure TButtonedEdit.CreateWnd; var Dummy: IUnknown; Strings: IEnumString; begin inherited; if HandleAllocated then begin try Dummy := CreateComObject(CLSID_AutoComplete); if (Dummy <> nil) and (Dummy.QueryInterface(IID_IAutoComplete, FAutoComplete) = S_OK) then begin case FACSource of acsHistory: Strings := CreateComObject(CLSID_ACLHistory) as IEnumString; acsMRU: Strings := CreateComObject(CLSID_ACLMRU) as IEnumString; acsShell: Strings := CreateComObject(CLSID_ACListISF) as IEnumString; else Strings := FACList as IEnumString; end; if S_OK = FAutoComplete.Init(Handle, Strings, nil, nil) then begin SetACEnabled(FACEnabled); SetACOptions(FACOptions); end; end; except //CLSID_IAutoComplete is not available end; end; end; destructor TButtonedEdit.Destroy; begin FACList := nil; inherited; end; procedure TButtonedEdit.DestroyWnd; begin if (FAutoComplete <> nil) then begin FAutoComplete.Enable(False); FAutoComplete := nil; end; inherited; end; function TButtonedEdit.GetACStrings: TStringList; begin Result := FACList.FStrings; end; procedure TButtonedEdit.SetACEnabled(const Value: Boolean); begin if (FAutoComplete <> nil) then begin FAutoComplete.Enable(FACEnabled); end; FACEnabled := Value; end; procedure TButtonedEdit.SetACOptions(const Value: TACOptions); const Options : array[TACOption] of integer = (ACO_AUTOAPPEND, ACO_AUTOSUGGEST, ACO_UPDOWNKEYDROPSLIST); var Option:TACOption; Opt: DWORD; AC2: IAutoComplete2; begin if (FAutoComplete <> nil) then begin if S_OK = FAutoComplete.QueryInterface(IID_IAutoComplete2, AC2) then begin Opt := ACO_NONE; for Option := Low(Options) to High(Options) do begin if (Option in FACOptions) then Opt := Opt or DWORD(Options[Option]); end; AC2.SetOptions(Opt); end; end; FACOptions := Value; end; procedure TButtonedEdit.SetACSource(const Value: TACSource); begin if FACSource <> Value then begin FACSource := Value; RecreateWnd; end; end; procedure TButtonedEdit.SetACStrings(const Value: TStringList); begin if Value <> FACList.FStrings then FACList.FStrings.Assign(Value); end; end.
And this is the result.
