How append rectangle to QGraphicView - c++

Question

How can I append new rectangle shape to QgraphicView In this code which create rectangle when the button click.But when I click the button second time previously created rectangle removed.I need to do create 2 rectangle when I click the button 2 times.create 3 rectangle when I click the button 3 times
void Widget::on_btnCreateRect_clicked()
{
scene = new QGraphicsScene(this);
ui->graphicsView->setScene(scene);
//QBrush redBrush(Qt::red);
QBrush blueBrush(Qt::blue);
QPen blackPen(Qt::black);
blackPen.setWidth(6);
rect = scene->addRect(-10,-10,100,100,blackPen,blueBrush);
rect->setFlag(QGraphicsItem::ItemIsMovable, true);
}

Answer 1

With scene = new QGraphicsScene(this); you create a new scene and add the rectangle to it. The old scene with the previous rectangles exist but is not shown anymore. So instead of creating a new scene use the old one like that: rect = ui->graphicsView->scene()->addRect(-10,-10,100,100,blackPen,‌​blueBrush);. This will also avoid the memory leak you create with new. Here is the corrected code:
void Widget::on_btnCreateRect_clicked()
{
//QBrush redBrush(Qt::red);
QBrush blueBrush(Qt::blue);
QPen blackPen(Qt::black);
blackPen.setWidth(6);
QRect *rect = ui->graphicsView->scene()->addRect(-10,-10,100,100,blackPen,‌​blueBrush);
rect->setFlag(QGraphicsItem::ItemIsMovable, true);
}