How do you paint two lines on QcustomPlot in QT in Ubuntu?

Question

I have Ubuntu 14.04, I'm working with QT C++ . I will paint two lines ( in QcustomPlot ) Each line has a different color from the other. I will to paint a line Red Then line green, like this My code :

customPlot->addGraph() ; // color red 
customPlot->addGraph() ; // color green 
customPlot->graph(0)->setPen(QPen(Qt::red));

customPlot->graph(1)->setPen(QPen(Qt::red));
customPlot->graph(1)->setPen(QPen(Qt::green);
customPlot->graphe(0)->adddata(1,1) ;  
customPlot->graphe(0)->adddata(5,1) ;  
customPlot->graphe(1)->adddata(5,1) ; 
customPlot->graphe(1)->adddata(10,1) ;  
customPlot->graphe(0)->adddata(10,1) ; 
customPlot->graphe(0)->adddata(15,1) ;  

The problem is that the red line painted on the green How to solve the problem?

Answer 1

 QCPItemLine *item ;
item = new QCPItemLine(ui->courbe);
customPlot->addItem(item);

item->setPen(QPen(Qt::red));
item->start->setCoords(1,1);
item->end->setCoords(5,1);

item = new QCPItemLine(ui->courbe);
item->start->setCoords(6,1);
item->end->setCoords(10,1);
customPlot->replot();