{private
    procedure DrawFocusRectangle(sender: TObject);
  public
    { Public declarations }
  end;}

var
  Form1: TForm1;
  FocusRectangle: TShape;

implementation

{$R *.dfm}

//窗体创建事件中加如下代码
procedure TForm1.FormCreate(Sender: TObject);
begin
  FocusRectangle := TShape.Create(Self);
  FocusRectangle.Shape := stRectangle;
  FocusRectangle.Visible := False;
  FocusRectangle.Brush.Style := bsClear;
  FocusRectangle.Pen.Style := psDot;
  FocusRectangle.Pen.Color := clRed;
  FocusRectangle.Pen.Width := 1;
{在Screen的OnActiveControlChange事件中处理}
  Screen.OnActiveControlChange := DrawFocusRectangle;
end;

procedure TForm1.DrawFocusRectangle;
begin
  with FocusRectangle do
  begin
    Parent := Screen.ActiveControl.Parent;
    Top := Screen.ActiveControl.Top -2 ;
    Height := Screen.ActiveControl.Height + 4;
    Left := Screen.ActiveControl.Left - 2;
    Width := Screen.ActiveControl.Width + 4;
    Visible := True;
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Screen.OnActiveControlChange := nil;
  FocusRectangle.Free;
end;