Sticks on plot not working

[giusepped]

I would like to plot vertical stick on my graph.
I tried according to the documentation:

plotEnergy = new QwtPlotCurve();
	plotEnergy->attach(this);
	plotEnergy->setStyle(QwtPlotCurve::Sticks);
	plotEnergy->setBaseline(0);
	plotEnergy->setPen(QPen(Qt::black));
	plotEnergy->setBrush(QBrush(Qt::Dense7Pattern));

plotEnergy = new QwtPlotCurve();
	plotEnergy->attach(this);
	plotEnergy->setStyle(QwtPlotCurve::Sticks);
	plotEnergy->setBaseline(0);
	plotEnergy->setPen(QPen(Qt::black));
	plotEnergy->setBrush(QBrush(Qt::Dense7Pattern));

To copy to clipboard, switch view to plain text mode 

But nothing: the plot still is plotted with lines