Problem drawing an Arrow using RArrow class (solved)

houmingc

error:: expected primary-expression before ')' token

Not able to draw an Arrow using rarrow class link as below:
https://rittwik.wordpress.com/2012/08/29/rarrow-class-for-drawing-arrows/

MainWindow::MainWindow
{
RArrow *Rarrow = new RArrow();
Rarrow-> raDrawArrow(QPainter);
}
raSetArrowHead use 3 raArrowsPoints[ ] to create Head
raSetArrowLine use 4 raArrowsPoints[ ] to create Rectangle.

Amend RArrow constructor as follow :
RArrow::RArrow()
{ raStartPoint = QPoint(5,5);
raEndPoint = QPoint(40,40);
raLineWidth = 20;
raHeadHeight = 5;
raBorderThickness =2 ;
for( int i=0;i<7;i++)
raArrowPoints[i]=QPointF(-1,-1);
}

Wieland

@houmingc said:

Rarrow-> raDrawArrow(QPainter);

You need to pass a pointer to the QPainter object you want to paint with. So, for example, if you want to draw on a custom widget then reimplement its paintEvent method like this:

void SimpleExampleWidget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setPen(Qt::blue);
    painter.setFont(QFont("Arial", 30));
    painter.drawText(rect(), Qt::AlignCenter, "Qt");
    // ...
    RArrow *Rarrow = new RArrow();
    Rarrow-> raDrawArrow(&painter);
}

houmingc

It work.
Can please briefly explain why pass a pointer QPainter object to the paint Object

---- To draw 3 arrow -----
QPainter painter(this);
Rarrow1->setStart(QPointF(100,110));
Rarrow1->setEnd(QPointF(150,110));
Rarrow1->raDrawArrow(&painter);

Rarrow1->setStart(QPointF(160,110));
Rarrow1->setEnd(QPointF(200,110));
Rarrow1->raDrawArrow(&painter);

Rarrow1->setStart(QPointF(250,110));
Rarrow1->setEnd(QPointF(300,110));
Rarrow1->raDrawArrow(&painter);

Wieland

Can please briefly explain why pass a pointer

Because the website you linked to says so. :-) It says:

After specifying these variables you can call the
void raDrawArrow(QPainter *)
function to draw the arrow using the QPainter.