WM_NCCALCSIZE:
 begin
  Style := GetWindowLong( frmMain.pnlDBJ_BT_CT.Handle, GWL_STYLE );
  If (Style and WS_HSCROLL) <> 0 Then
   SetWindowLong( frmMain.pnlDBJ_BT_CT.Handle, GWL_STYLE, Style and not WS_HSCROLL );
//    SetWindowLong( frmMain.pnlDBJ_BT_CT.Handle, GWL_STYLE, Style or WS_VSCROLL );
  inherited;
//   Result := true;
 end;

Result := true;

SetWindowLong( frmMain.pnlDBJ_BT_CT.Handle, GWL_STYLE, Style or WS_VSCROLL );

  WM_NCCALCSIZE:
     ShowScrollBar(tv.Handle,SB_HORZ,False);

 WM_NCCALCSIZE:
    ShowScrollBar(tv.Handle,SB_HORZ,False)

unit Unit1;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, ComCtrls;

type
 TMyTreeView = class(TTreeView)
 private
   procedure WMNCCalcSize(var Message: TMessage); message WM_NCCALCSIZE;
 end;

type
 TForm1 = class(TForm)
   procedure FormCreate(Sender: TObject);
 private
   MyTreeView: TMyTreeView;
 public
   { Public declarations }
 end;

var
 Form1: TForm1;

implementation

{$R *.dfm}

{ TMyTreeView }

procedure TMyTreeView.WMNCCalcSize(var Message: TMessage);
begin
 ShowScrollBar(Handle,SB_HORZ,False);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 MyTreeView := TMyTreeView.Create(Self);
 MyTreeView.Parent := Self;
end;

end.

TMyTreeView = class(TTreeView)
private
 Procedure WMNCCalcSize( Var msg: TMessage ); message WM_NCCALCSIZE;
end;

procedure TMyTreeView.WMNCCalcSize(var msg: TMessage);
var
 style: Integer;
begin
 style := getWindowLong( handle, GWL_STYLE );
 If (style and WS_HSCROLL) <> 0 Then
   SetWindowLong( handle, GWL_STYLE, style and not WS_HSCROLL );
 inherited;
end;