Old image stays when drawing new one

BobMarly

i want my program to show a different drawing for every item in the combobox, and it does, but the previous drawing always stays when i choose the next item in the combobox, so eventually there are a lot of drawings, but i only want the one that i selected.
@void MWidget::ChangeFile(int NewIndex)
{
if(NewIndex<airfoils.count())
{
ReadFile(airfoils.at(NewIndex));

    update();

}

}
//![0]
void MWidget::ReadFile(QString thefile)

{
m_File_p = new QFile (thefile);

if (m_File_p != NULL)
{
    if ( (m_File_p->exists() == true) &&
         (m_File_p->open(QIODevice::ReadOnly | QIODevice::Text) == true) )
    {

        QTextStream stream(m_File_p);
        QString line = stream.readLine();

        bool blnFirstLine =true;
        float flScale = 640;
        while (!line.isNull())
        {

            if(blnFirstLine)
            {
                blnFirstLine=false;
            }else{

                QStringList coordinates = line.split(",", QString::SkipEmptyParts );

                if( coordinates.count() == 2 )
                {
                    bool checkX;
                    float x = coordinates.at(0).trimmed().toFloat( &checkX )*flScale+100;
                    bool checkY;
                    float y = coordinates.at(1).trimmed().toFloat( &checkY )*(-1)*flScale+100;

                    if( checkX && checkY )
                        polyPoints  << QPointF(x,y);
                }
            }

            line = stream.readLine();


        }

    }
    m_File_p->flush();
    m_File_p->close();
    delete  m_File_p;

}

}

//![0]
//![1]
MWidget::~MWidget()
{
delete ui;

}
//![1]
//![2]
QSize MWidget::sizeHint() const
{
return QSize(840, 480);

}
//![2]
//![3]
void MWidget::paintEvent(QPaintEvent * event)
{

QWidget::paintEvent(event);

setAttribute(Qt::WA_OpaquePaintEvent);
// i found the QLabel idea online, but it doesnt seem to do anything
QLabel *label = new QLabel(this);
label->setAutoFillBackground(true);

QPainter painter(this);

painter.setRenderHint(QPainter::Antialiasing,true);
QPen linepen(Qt::red);
linepen.setCapStyle(Qt::RoundCap);
linepen.setWidth(5);
painter.setPen(linepen);

painter.drawPolyline(polyPoints2);

update();

}@

Asperamanca

Something is not right, or your code is not complete:
You stream into "polyPoints", but in paintEvent, you use "polyPoints2".

Do you ever clear polyPoints?

BobMarly

it was just a copying mistake, should be polypoints

onmouse

it's seems like syntax?

victim123

dont know.