painter not active

[athulms]

i used the code add when i run the program it shows painter is not active
what is the solution for this error.

void mainwindow::paintEvent(QPaintEvent *e)
{
 
    QPainter painter(this);
    QPen linepen(Qt::red);
    linepen.setCapStyle(Qt::RoundCap);
    linepen.setWidth(30);
    painter.setRenderHint(QPainter::Antialiasing,true);
    painter.setPen(linepen);
    painter.drawPoint(100,100);
 
}

void mainwindow::paintEvent(QPaintEvent *e)
{

    QPainter painter(this);
    QPen linepen(Qt::red);
    linepen.setCapStyle(Qt::RoundCap);
    linepen.setWidth(30);
    painter.setRenderHint(QPainter::Antialiasing,true);
    painter.setPen(linepen);
    painter.drawPoint(100,100);

}

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waiting response