Probleme mit Custom Propertyeditor für ComboBox

[Neutral General]

Ich hab mal ganz grob (die in meinen Augen) wichtigsten Codestellen rausgesucht:

Delphi-Quellcode:

type
  TMyComboBoxStrings = class(TCustomComboBoxStrings)
  private
    FMapValues: TList<TValue>;
  public
    function AddMapped(const S: String; AValue: TValue): Integer;
    // ..
  end;

  TMyComboBox = class(TComboBox)
  protected
    function GetItemsClass: TCustomComboBoxStringsClass; override;
    procedure DefineProperties(Filer: TFiler); override;
    procedure ReadMapList(Stream: TStream);
    procedure WriteMapList(Stream: TStream);
  end;

implementation

function TMyComboBox.GetItemsClass: TCustomComboBoxStringsClass;
begin
  Result := TMyComboBoxStrings;
end;

procedure TMyComboBox.DefineProperties(Filer: TFiler);
begin
  inherited;
  Filer.DefineBinaryProperty('MappedValues',ReadMapList, WriteMapList, Items.Count > 0);
end;

Property-Editor:

Delphi-Quellcode:

// Form was beim Klick auf "..." im Propertyeditor aufgerufen wird
TMyComboBoxItemEditForm = class(TForm)
  // ...
end;

TMyComboBoxItemEditor = class(TPropertyEditor)
public
  procedure Edit; override;
  function GetAttributes: TPropertyAttributes; override;
  function GetValue: String; override;
end;

implementation

procedure TMyComboBoxItemEditor.Edit;
var tmpForm: TMyComboBoxItemEditForm;
    tmpStrings: TMyComboBoxStrings;
begin
  inherited;

  tmpStrings := TMyComboBoxStrings(GetOrdValue);
  if Assigned(tmpStrings) then
  begin
    tmpForm := TMyComboBoxItemEditForm.Create(Application, TMyComboBox(GetComponent(0)), tmpStrings);
    try
      if tmpForm.ShowModal = mrOK then
      begin
        SetOrdValue(Integer(tmpForm.GetResultList()));
        Modified;
      end;
    finally
      tmpForm.Free;
    end;
  end;
end;

function TMyComboBoxItemEditor.GetAttributes: TPropertyAttributes;
begin
  Result := inherited GetAttributes + [paDialog];
end;

function TMyComboBoxItemEditor.GetValue: String;
begin
  if GetOrdValue <> 0 then
    Result := '<' + TObject(GetOrdValue).ClassName + '>'
  else
    Result := '-';
end;

procedure Register;
begin
  RegisterPropertyEditor(TypeInfo(TStrings), TMyComboBox, '', TMyComboBoxItemEditor);
end;