draw points on mouse click shows error painter not active.

void MainWindow::mousePressEvent(QMouseEvent *e)
{
if(e->button()==Qt::LeftButton)
{
QPoint point = e->pos();
int x=point.rx();
int y=point.ry();
QPainter painter(this);
QPen linepen(Qt::red);
linepen.setWidth(30);
linepen.setCapStyle(Qt::RoundCap);
painter.setRenderHint(QPainter::Antialiasing,true) ;
painter.setPen(linepen);
painter.drawPoint(x,y);
}
}


What is the error in the code. Waiting for rply.

The reason of the error is using QPainter not inside paintEvent().Move the drawing to the paintEvent(),here in mousePressEvent just save points to draw on some list or so.

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


void MainWindow::mousePressEvent(QMouseEvent *e)
{
if(e->button()==Qt::LeftButton)
{
QPoint point = e->pos();
int x=point.rx();
int y=point.ry();
QPainter painter(this);
painter.drawPoint(x,y);
}
}


This also shows the same error

Of course it shows the same error,as you have not corrected it

Quote:

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Originally Posted by athulms

void MainWindow::mousePressEvent(QMouseEvent *e)
{
if(e->button()==Qt::LeftButton)
{
QPoint point = e->pos();
int x=point.rx();
int y=point.ry();
QPainter painter(this);//this is fckig wrong.QPainter instances may not be created outside the paintEvent
painter.drawPoint(x,y);
}
}

---

ya i have used the update(); method. now it worked