Subclassing QGraphicsLayoutItem

Question

How exactly can I subclass QGraphicsLayoutItem? I write a class that subclass QGraphicsLayoutItem and reimplement sizeHint and setGeometry but when I add my custom item to linear or grid layout. It does not shown? What is missing?

Here is my trial.

//basicitem.h 
#include <QGraphicsWidget> 
#include <QtCore/QRectF> 
#include <QtGui/QPainter> 
#include <QtGui/QBrush> 
#include <QtGui/QPen> 
#include <QtCore/QSizeF> 

class BasicItem : public QGraphicsWidget 
{ 
 public: 
BasicItem(qreal x1,qreal y1,qreal x2,qreal y2); 
~BasicItem(); 
QRectF boundingRect() const; 
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = 0); 
QSizeF sizeHint(Qt::SizeHint which, const QSizeF &constraint = QSizeF()) const; 
 private: 
    qreal x1,y1,x2,y2; 
 };

//basicitem.cpp  
#include "basicitem.h" 
#include <math.h> 
BasicItem::BasicItem(qreal x1, qreal y1, qreal x2, qreal y2) 
 {  
this->x1 = x1; 
this->y1 = y1; 
this->x2 = x2; 
this->y2 = y2; 
 } 
BasicItem::~BasicItem() 
 { 
 } 
QRectF BasicItem::boundingRect() const 
 { 
     return QRectF(x1,y1,abs(x2-x1),5); 
 }
 void BasicItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) 
 { 
     Q_UNUSED(option); 
     Q_UNUSED(widget); 
     painter->setRenderHint(QPainter::Antialiasing); 
    painter->setPen(QPen(QBrush(Qt::yellow),4,Qt::SolidLine,Qt::FlatCap,Qt::BevelJoin)); 
 painter->drawLine(x1,y1,x2,y2); 
 } 

 QSizeF BasicItem::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const 
 { 
    Q_UNUSED(which); 
    Q_UNUSED(constraint); 
    return QSizeF(abs(x2-x1),5); 
 }

 //compositeitem.h 
 #include <QGraphicsItemGroup> 
 #include <QGraphicsLayoutItem> 
 #include <QSizeF> 
 #include <QList> 

 #include "basicitem.h" 

 class CompositeItem:public QGraphicsItemGroup,public QGraphicsLayoutItem 
 { 
   public: CompositeItem(QList<BasicItem *> children); 
   ~CompositeItem(); 
    QSizeF sizeHint(Qt::SizeHint which, const QSizeF &constraint = QSizeF()) const; 
    void setGeometry(const QRectF &rect); 
    void updateGeometry(); 
 };

 //compositeitem.cpp  
 #include "compositeitem.h" 
 CompositeItem::CompositeItem(QList<BasicItem *> children) 
 { 
    BasicItem *child; 
    foreach(child,children) 
    { 
      addToGroup(child); 
    } 
} 
CompositeItem::~CompositeItem() 
{ 
} 
QSizeF CompositeItem::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const 
{ 
    Q_UNUSED(which); 
    Q_UNUSED(constraint); 
    //Arbitrary values but big enough 
    return QSizeF(300,300); 
}

void CompositeItem::setGeometry(const QRectF &rect) 
{ 
  Q_UNUSED(rect); 
  QGraphicsLayoutItem::setGeometry(QRectF(0,0,300,300)); 
} 

void CompositeItem::updateGeometry() 
{ 
  QGraphicsLayoutItem::updateGeometry(); 
}

//mainwindow.cpp - important parts
...
QGraphicsScene *scene = new QGraphicsScene; 
ui->graphicsView->setScene(scene); 
BasicItem *basic1 = new BasicItem(10,400,110,400); 
BasicItem *basic2 = new BasicItem(10,400,110,500); 
QList<BasicItem *> basicItemList; 
basicItemList.push_back(basic1); 
basicItemList.push_back(basic2); 
CompositeItem *ci = new CompositeItem(basicItemList); 
QGraphicsLinearLayout *layout = new QGraphicsLinearLayout; 
layout->addItem(ci); 
QGraphicsWidget *container = new QGraphicsWidget; 
container->setLayout(layout); 
scene->addItem(container); 
...