[vtkusers] Changing the active cell-attributes and updating the view

[Jens]

Hi
Can anybody tell me how to change the active cell-attributes and updating the 
view.

I tried (zfsData is a subclass of vtkUnstructuredGridAlgorithmn)
	zfsData->GetOutput()->GetCellData()->SetActiveScalars( attName );
which works fine if I use it _before_
	ren->GetRenderWindow()->Render()

But if I want the user to change the active scalars and call the following 
function nothing happens (all cells stay white):

void View::changeAttribute(const char* attName)
{
	this->zfsData->GetOutput()->GetCellData()->SetActiveScalars( attName );
	this->zfsMapper->SetScalarRange( zfsData->GetOutput()->GetScalarRange() );
	this->ren->Render();
}

If seems as if Render() does not update the colors of the cells.
Any idea anybody?
		Greetings
			Jens