Why the signal "dataChanged" by QTableWidget not work?

Hello, I am modifying the example "Chart" so that when I change data in the table, another function "Display()" can be executed. Below is my modification to MainWindow.cpp (line #17 is added to the original code):

Code:

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MainWindow::MainWindow()
{
    QMenu *fileMenu = new QMenu(tr("&File"), this);
    QAction *openAction = fileMenu->addAction(tr("&Open..."));
    openAction->setShortcuts(QKeySequence::Open);
    QAction *saveAction = fileMenu->addAction(tr("&Save As..."));
    saveAction->setShortcuts(QKeySequence::SaveAs);
    QAction *quitAction = fileMenu->addAction(tr("E&xit"));
    quitAction->setShortcuts(QKeySequence::Quit);
 
    setupModel();
    setupViews();
 
    connect(openAction, SIGNAL(triggered()), this, SLOT(openFile()));
    connect(saveAction, SIGNAL(triggered()), this, SLOT(saveFile()));
    connect(quitAction, SIGNAL(triggered()), qApp, SLOT(quit()));
    connect (model,SIGNAL(dataChanged(const QModelIndex & topLeft, const QModelIndex & bottomRight)),this,SLOT(display(const QModelIndex & topLeft, const QModelIndex & bottomRight)));
    menuBar()->addMenu(fileMenu);
    statusBar();
 
    openFile(":/Charts/qtdata.cht");
 
    setWindowTitle(tr("Chart"));
    resize(870, 550);
}

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I am therefore expecting the following function written by my own (and added to prive slot in MainWindow.h) will be executed once I change data in the table view:

Code:

---

void  display(const QModelIndex & topLeft, const QModelIndex & bottomRight);

---

However, I found whatever I did to the data in the table view during execution of the main program, the display() function would never be triggered. Could anyone help me with this. I am using Qt 4.7 with visual studio 2008. Thank you very much.

I understand, It should be

connect(model, SIGNAL(dataChanged ( const QModelIndex &, const QModelIndex & )),
this, SLOT( backgroundChanged ( const QModelIndex & , const QModelIndex & )));

Then it works.