How to redraw QGraphicsScene background in running

[wisconxing]

In my QGraphicsScene object declare, I have draw a picture in drawBackground(), see below:

class MyScene : public QGraphicsScene
{    
public: 
    MyScene(qreal x, qreal y, qreal w, qreal h)
          : QGraphicsScene(x, y, w, h)      { } 
 
protected:
    void drawBackground(QPainter *painter, const QRectF &rect)
{    //draw an old  background
};

class MyScene : public QGraphicsScene
{    
public: 
    MyScene(qreal x, qreal y, qreal w, qreal h)
          : QGraphicsScene(x, y, w, h)      { } 

protected:
    void drawBackground(QPainter *painter, const QRectF &rect)
{    //draw an old  background
};

To copy to clipboard, switch view to plain text mode 

In my program running, I need redraw the background, how I will do?
Very Thanks