I want to show how to create the combobox with popup tree.

(sorry foe my bad English)  ^)

unit dkTreeBox;

interface
uses Classes, Graphics, {Types,} ComCtrls,
Controls, Windows, SysUtils, Messages, Forms,ImgList;
type
  TdkTreeBox = class;

  TdkListView = class(TCustomTreeView)
  private
    FEdit: TdkTreeBox;
    procedure WMKillFocus(var Message: TMessage); message WM_KILLFOCUS;
  protected
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState;
      X, Y: Integer); override;
    procedure MouseMove(Shift: TShiftState; X, Y: Integer); override;
    procedure KeyPress(var Key: Char); override;
    procedure CreateParams(var Params: TCreateParams); override;
  public
    constructor Create(AOwner: TComponent); override;
  end;

  TdkTreeBox = class(TCustomControl)
  private
    FPopupList: TdkListView;
    FListVisible: Boolean;
    FText: string;
    FButtonWidth: Integer;
    FPressed: Boolean;
    FHasFocus: Boolean;
    FAlignment: TAlignment;
    FOnDropDown: TNotifyEvent;
    FOnCloseUp: TNotifyEvent;
    procedure SetAlignment(const Value: TAlignment);
    procedure WMSetFocus(var Message: TMessage); message WM_SETFOCUS;
    procedure WMKillFocus(var Message: TMessage); message WM_KILLFOCUS;
    procedure SetOnCloseUp(const Value: TNotifyEvent);
    procedure SetOnDropDown(const Value: TNotifyEvent);
    function GetItems: TTreeNodes;
    procedure SetItems(const Value: TTreeNodes);
    function GetImages: TCustomImageList;
    function GetStateImages: TCustomImageList;
    procedure SetImages(const Value: TCustomImageList);
    procedure SetStateImages(const Value: TCustomImageList);
    function GetListHeight: Integer;
    procedure SetListHeight(const Value: Integer);
  protected
    procedure KeyDown(var Key: Word; Shift: TShiftState); override;
    procedure KeyUP(var Key: Word; Shift: TShiftState); override;
    procedure KeyPress(var Key: Char); override;
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState;
      X, Y: Integer); override;
    procedure MouseMove(Shift: TShiftState; X, Y: Integer); override;
    procedure MouseUp(Button: TMouseButton; Shift: TShiftState;
      X, Y: Integer); override;
    procedure Paint; override;
    procedure CreateParams(var Params: TCreateParams); override;
    procedure DropDown; virtual;
    procedure CloseUp(Accept: Boolean); virtual;
  public
    constructor Create(AOwner: TComponent); override;
    property Text: string read FText;
  published
    property Alignment: TAlignment read FAlignment write SetAlignment;
    property OnDropDown: TNotifyEvent read FOnDropDown write SetOnDropDown;
    property OnCloseUp: TNotifyEvent read FOnCloseUp write SetOnCloseUp;
    property Items: TTreeNodes read GetItems write SetItems;
    property Images: TCustomImageList read GetImages write SetImages;
    property StateImages: TCustomImageList read GetStateImages write SetStateImages;
    property ListHeight:Integer read GetListHeight write SetListHeight;
    property Anchors;
    property BiDiMode;
    property Color;
    property Constraints;
    property Ctl3D;
    property DragCursor;
    property DragKind;
    property DragMode;
    property Enabled;
    property Font;
    property ImeMode;
    property ImeName;
    property ParentBiDiMode;
    property ParentColor;
    property ParentCtl3D;
    property ParentFont;
    property ParentShowHint;
    property PopupMenu;
    property ShowHint;
    property Visible;
    property OnClick;
    property OnContextPopup;
    property OnDragDrop;
    property OnDragOver;
    property OnEndDock;
    property OnEndDrag;
    property OnEnter;
    property OnExit;
    property OnKeyDown;
    property OnKeyPress;
    property OnKeyUp;
    property OnMouseDown;
    property OnMouseMove;
    property OnMouseUp;
    property OnStartDock;
    property OnStartDrag;
  end;
procedure Register;
implementation

{ TdkTreeBox }
procedure Register;
begin
RegisterComponents('DelphiKindomDemo',[TdkTreeBox]);
end;

procedure TdkTreeBox.CloseUp(Accept: Boolean);
begin
  SetFocus;
  if Accept and Assigned(FPopupList.Selected) then
    FText := FPopupList.Selected.Text;
  SetWindowPos(FPopupList.Handle, 0, 0, 0, 0, 0, SWP_NOZORDER or
    SWP_NOMOVE or SWP_NOSIZE or SWP_NOACTIVATE or SWP_HIDEWINDOW);
  FListVisible := False;
  if Assigned(FOnCloseUp) then FOnCloseUp(Self);
  Repaint;
end;

constructor TdkTreeBox.Create(AOwner: TComponent);
begin
  inherited;
  FButtonWidth := GetSystemMetrics(SM_CXVSCROLL);
  ControlStyle := ControlStyle + [csReplicatable];
  if NewStyleControls then
    ControlStyle := [csOpaque]
  else
    ControlStyle := [csOpaque, csFramed];
  ParentColor := False;
  TabStop := True;
  FPopupList := TdkListView.Create(Self);
  FListVisible := False;
  FPopupList.HideSelection := True;
  Height:=24;
end;

procedure TdkTreeBox.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  with Params do
    if NewStyleControls and Ctl3D then
      ExStyle := ExStyle or WS_EX_CLIENTEDGE
    else
      Style := Style or WS_BORDER;
end;

procedure TdkTreeBox.DropDown;
var
  P: TPoint;
  Y: Integer;
begin
  if Assigned(FOnDropDown) then FOnDropDown(Self);
  FPopupList.Color := Color;
  FPopupList.Font := Font;
  FPopupList.Width := Width;
  FListVisible := True;
  P := Parent.ClientToScreen(Point(Left, Top));
  Y := P.Y + Height;
  if Y + FPopupList.Height > Screen.Height then Y := P.Y - FPopupList.Height;
  SetWindowPos(FPopupList.Handle, HWND_TOP, P.X, Y, 0, 0,
    SWP_NOSIZE or SWP_SHOWWINDOW);
  FPopupList.Repaint;
end;

function TdkTreeBox.GetImages: TCustomImageList;
begin
Result:=FPopupList.Images;
end;

function TdkTreeBox.GetItems: TTreeNodes;
begin
  Result := FPopupList.Items;
end;

function TdkTreeBox.GetListHeight: Integer;
begin
Result:=FPopupList.Height;
end;

function TdkTreeBox.GetStateImages: TCustomImageList;
begin
Result:=FPopupList.StateImages;
end;

procedure TdkTreeBox.KeyDown(var Key: Word; Shift: TShiftState);
begin
  inherited;
  FPressed := True;
  Invalidate;
  if not FlistVisible then
    DropDown
  else
    CloseUp(False);
end;

procedure TdkTreeBox.KeyPress(var Key: Char);
begin
  inherited;
end;


procedure TdkTreeBox.KeyUP(var Key: Word; Shift: TShiftState);
begin
  inherited;
  Invalidate;
end;

procedure TdkTreeBox.MouseDown(Button: TMouseButton; Shift: TShiftState; X,
  Y: Integer);
begin
  inherited;
  FPressed := True;
  Invalidate;
  if not FlistVisible then
    DropDown
  else
    CloseUp(False);
end;

procedure TdkTreeBox.MouseMove(Shift: TShiftState; X, Y: Integer);
begin
  inherited;


end;

procedure TdkTreeBox.MouseUp(Button: TMouseButton; Shift: TShiftState; X,
  Y: Integer);
begin
  inherited;
  Invalidate;
end;

procedure TdkTreeBox.Paint;
var
  W, X, Flags: Integer;
  Selected: Boolean;
  R: TRect;
begin
  Canvas.Font := Font;
  Canvas.Brush.Color := Color;
  if Enabled then
    Canvas.Font.Color := Font.Color
  else
    Canvas.Font.Color := clGrayText;
  Selected := FHasFocus;
  if Selected then
  begin
    Canvas.Font.Color := clHighlightText;
    Canvas.Brush.Color := clHighlight;
  end;
  if (csDesigning in ComponentState) then
    FText := Name;

  if UseRightToLeftAlignment then ChangeBiDiModeAlignment(FAlignment);
  W := ClientWidth - FButtonWidth;
  X := 2;
  case Alignment of
    taRightJustify: X := W - Canvas.TextWidth(Text) - 3;
    taCenter: X := (W - Canvas.TextWidth(Text)) div 2;
  end;
  SetRect(R, 1, 1, W - 1, ClientHeight - 1);
  if (SysLocale.MiddleEast) and (BiDiMode = bdRightToLeft) then
  begin
    Inc(X, FButtonWidth);
    Inc(R.Left, FButtonWidth);
    R.Right := ClientWidth;
  end;
  if SysLocale.MiddleEast then TControlCanvas(Canvas).UpdateTextFlags;
  Canvas.TextRect(R, X, 2, Text);
  if Selected then Canvas.DrawFocusRect(R);
  SetRect(R, W, 0, ClientWidth, ClientHeight);
  if (SysLocale.MiddleEast) and (BiDiMode = bdRightToLeft) then
  begin
    R.Left := 0;
    R.Right := FButtonWidth;
  end;
  if not Enabled then
    Flags := DFCS_SCROLLCOMBOBOX or DFCS_INACTIVE
  else if FPressed then
    Flags := DFCS_SCROLLCOMBOBOX or DFCS_FLAT or DFCS_PUSHED
  else
    Flags := DFCS_SCROLLCOMBOBOX;
  DrawFrameControl(Canvas.Handle, R, DFC_SCROLL, Flags);
  FPressed := False;
end;

procedure TdkTreeBox.SetAlignment(const Value: TAlignment);
begin
  FAlignment := Value;
end;

procedure TdkTreeBox.SetImages(const Value: TCustomImageList);
begin
FPopupList.Images:=Value;
end;

procedure TdkTreeBox.SetItems(const Value: TTreeNodes);
begin
  FPopupList.Items.Assign(Value);
end;

procedure TdkTreeBox.SetListHeight(const Value: Integer);
begin
FPopupList.Height:=Value;
end;

procedure TdkTreeBox.SetOnCloseUp(const Value: TNotifyEvent);
begin
  FOnCloseUp := Value;
end;

procedure TdkTreeBox.SetOnDropDown(const Value: TNotifyEvent);
begin
  FOnDropDown := Value;
end;

procedure TdkTreeBox.SetStateImages(const Value: TCustomImageList);
begin
FPopupList.StateImages:=Value;
end;

procedure TdkTreeBox.WMKillFocus(var Message: TMessage);
begin
  FHasFocus := False;
  inherited;
  if not FPopupList.Focused then CloseUp(True);
end;

procedure TdkTreeBox.WMSetFocus(var Message: TMessage);
begin
  FHasFocus := True;
  inherited;
  Invalidate;
end;

{ TdkListView }

constructor TdkListView.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FEdit := TdkTreeBox(AOwner);
  Parent := FEdit;
  Visible := False;
  ControlStyle := ControlStyle + [csNoDesignVisible, csReplicatable];
end;

procedure TdkListView.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  with Params do
  begin
    Style := Style or WS_POPUP or WS_VSCROLL or WS_BORDER;
    ExStyle := WS_EX_TOOLWINDOW;
    AddBiDiModeExStyle(ExStyle);
    WindowClass.Style := CS_SAVEBITS;
  end;

end;

procedure TdkListView.KeyPress(var Key: Char);
begin
  inherited;
  if (Key = #13) or (Key = #32) then FEdit.CloseUp(True);
  if Key = #27 then FEdit.CloseUp(False);
end;

procedure TdkListView.MouseDown(Button: TMouseButton; Shift: TShiftState;
  X, Y: Integer);
var
  VNode: TTreeNode;
  VCanClose: Boolean;
  R: Trect;
begin
  inherited;
  VNode := GetNodeAt(x, y);
  if Assigned(VNode) then
  begin
    R := VNode.DisplayRect(True);
    VCanClose := (R.TopLeft.X < X) and
      (R.TopLeft.y < y);
       if VCanClose then
      FEdit.CloseUp(True);
  end;
end;

procedure TdkListView.MouseMove(Shift: TShiftState; X, Y: Integer);
begin
  inherited;
  Selected := GetNodeAt(x, y);
  
end;

procedure TdkListView.WMKillFocus(var Message: TMessage);
begin
  inherited;
  try
    FEdit.SetFocus;
  except
  end;
end;



end.