MouseEnter/Leave bei Pie

[Nic2012]

Besten Dank, aber in das MouseLeave geht der Code bei D7 nicht rein.
Ich habe versucht die PaintBox abzuleiten um MouseLeave/Enter published zu bekommen. Im FormCreate versuche ich auf die abgeleitete PaintBox zu casten, erhalte aber eine ungültige Typumwandlung:

Code:

type

  TPie = Record
    StartAngle, EndAngle: Double;
  ...
  End;
  ...
  TPaintBoxEx = class(TPaintBox)
  private
    FOnMouseEnter,
    FOnMouseLeave: TNotifyEvent;
    procedure CMMouseEnter (var mMsg : TMessage); message CM_MouseEnter;
    procedure CMMouseLeave (var mMsg : TMessage); message CM_MouseLeave;
  published
    property OnMouseEnter: TNotifyEvent READ FOnMouseEnter WRITE FOnMouseEnter;
    property OnMouseLeave: TNotifyEvent READ FOnMouseLeave WRITE FOnMouseLeave;
  end;

  TForm1 = class(TForm)
    PaintBox1: TPaintBox;
    ...
  private
    FPieArray: TPieArray;
    FMA: Double;
  end;

...

implementation

{$R *.dfm}

procedure TPaintBoxEx.CMMouseEnter(var mMsg : TMessage);
begin
  if Assigned(FOnMouseEnter) then FOnMouseEnter(Self);
end;

procedure TPaintBoxEx.CMMouseLeave(var mMsg : TMessage);
begin
  if Assigned(FOnMouseLeave) then FOnMouseLeave(Self);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  DoubleBuffered := true;

  SetLength(FPieArray, 4);
  ...

  (PaintBox1 as TPaintBoxEx).FOnMouseLeave := PaintBox1MouseLeave;

end;

procedure TForm1.PaintBox1MouseLeave(Sender: TObject);
begin
  FMA := -1;
end;