title: QGraphicsTextItem mouseDoubleClickEvent
body: <p>I am a new guy for QT. Now a question confuses me.</p>
  
  <p>Code in the MainWindow as follows:</p>
  
  <pre><code>MainWindow::MainWindow(QWidget *parent)
      : QMainWindow(parent)
  {
      QGraphicsView *view = new QGraphicsView;
      QGraphicsScene *scene =new QGraphicsScene;
      GraphicsTextItem *item = (GraphicsTextItem*)scene-&gt;addText(QString("hello world"));
      item-&gt;setPos(100,100);
      scene-&gt;addItem(item);
      QGraphicsItem *i = scene-&gt;itemAt(120,110);
      view-&gt;setScene(scene);
      view-&gt;show();
  }
  </code></pre>
  
  <p>class GraphicsTextItem inherits QGraphicsTextItem and protected method mousePressDown is reimplemented as follows:</p>
  
  <pre><code>void GraphicsTextItem::mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event)
  {
      qDebug()&lt;&lt;"mouseDoubleClickEvent happens";
      QGraphicsTextItem::mouseDoubleClickEvent(event);
  }
  </code></pre>
  
  <p>The application can works normally, but when I give the GraphicsTextItem object double click, nothing happens to the  mouseDoubleClickEvent in class GraphicsTextItem.</p>
  
  <p>Be expecting your response!</p>