在QPixmap上使用QPainter时应用崩溃

Question

I am trying to make a class that will make a dot graphic. The class inherits from QWidget. I want it to draw lines and dots on a QPixmap that will be displayed in a QLabel.

The constructor of the class looks like this:

MyClass::MyClass()
{
    calcul_proprietes(); // Function that makes calculation of what to draw.
    pix = new QPixmap(760,350);

    dessiner_graphique(); // Function that does the drawing.

    //Displaying the qpixmap
    layout_principal = new QVBoxLayout(this);
    label_pix = new QLabel(this);
    label_pix->setPixmap(*pix);
    layout_principal->addWidget(label_pix);
    this->setLayout(layout_principal);
}

And a short part of the function that does the drawing

void MyClass::dessiner_graphique()
{
    // ...
    QPainter painter(pix);
    QRect contour(x_depart,y_depart,largeur_grille,hauteur_grille);
    painter.drawRect(contour);
    // ...
}

I don't want to use the paintEvent function because it gets called all the time and i only need my graphic to be painted once. What do i do wrong?

Answer 1

Did you call the default base class constructor before Your class constructor ?

MyClass( QObject *parent )
: QWidget( parent )
{
    // Your posted code.
}