[SOLVED]QTableModel crashes on headerData

[RDiGuida]

I am trying to implement a really simple Table Model inheriting from a QAbstractTableModel which looks like this

#include <QAbstractTableModel>
#include <QStringList>

class ViewModel : public QAbstractTableModel
{
    Q_OBJECT
public:
    ViewModel(QList<QStringList>* mat, QStringList* cnames, QStringList* rnames, QObject *parent=0);
    virtual QVariant headerData (int section, Qt::Orientation orientation, int role = Qt::DisplayRole ) const;
    virtual int rowCount ( const QModelIndex & parent = QModelIndex() ) const;
    virtual int columnCount ( const QModelIndex & parent = QModelIndex() ) const;
    virtual QVariant data ( const QModelIndex & index, int role = Qt::DisplayRole ) const;

signals:

public slots:

private:
    QStringList* colnames;
    QStringList* rownames;
    QList<QStringList>* sourceMat;
};

Implemented as

ViewModel::ViewModel(QList<QStringList>* mat, QStringList* cnames, QStringList* rnames,QObject *parent)
    :QAbstractTableModel(parent)
{
    if(mat->count()!=rnames->count() || mat->at(0).count()!=cnames->count())
        return;

    sourceMat = mat;
    colnames = cnames;
    rownames = rnames;
}

int ViewModel::rowCount(const QModelIndex &parent ) const
{
    Q_UNUSED(parent);
    return sourceMat->count();  //last line is empty
}

int ViewModel::columnCount(const QModelIndex &parent ) const
{
    Q_UNUSED(parent);
    return sourceMat->at(0).count();
}

QVariant ViewModel::headerData(int section,
            Qt::Orientation orientation, int role) const
{
    if (role != Qt::DisplayRole)
            return QVariant();

    qDebug() << orientation << " " << section;

    if (orientation == Qt::Horizontal)
        return colnames->at(section);
    else
        return rownames->at(section);
}

I think the problem is in the headerData as the rownames and colnames are correct the first times the function is called but when the function gets called for a second iteration (I have no idea why) the rownames and colnames are not accessible anymore. Also - the data function is never reached.

The model is called with a single column and 24 rows and attached to a QTableView

ViewModel* mod_meta = new ViewModel(mat_meta,&cnamMet,data.rnames);

QTableView* tview = new QTableView;

tview->setModel(mod_meta);
QGridLayout* gl = new QGridLayout;
gl->addWidget(tview,0,0);

delete frame->layout();   // delete previous layout 
frame->setLayout(gl);

[mrjj]

@RDiGuida said:
Hi, is cnamMet and data.rnames part of a class so that they remain valid
for the life time of the Model?

[RDiGuida]

Thanks, that was the problem! I converted the private members into QStringList rather than QStringList*

[mrjj]

@RDiGuida
hi
you made the
QStringList* colnames;
QStringList* rownames;
in ViewModel
to
QStringList colnames;
QStringList rownames;
?

[RDiGuida]

Yes, and I passed the pointer dereferenced.

[mrjj]

@RDiGuida
Ok. it is fine. as you long as you are aware that its
most likely a copy the model have then.
so if you change cnamMet or data.rnames in main program, the model
still uses the original ones. (its copy)

[RDiGuida]

@mrjj I know thanks, the only thing that puzzles me is that it works if I keep sourceMat as pointer while it should have the same problems of rownames and colnames.

[mrjj]

@RDiGuida said:
Ok. super.
Me too.
In this line
ViewModel* mod_meta = new ViewModel(mat_meta,&cnamMet,data.rnames);
the variables cnamMet and data.rnames. where are they declared? (lives) ?

[RDiGuida]

cnamMet is declared in the same function where the model is initialised while data.rnames is declared in another class which is initialised outside of the function

[mrjj]

@RDiGuida
Ok, so cnamMet would run out of scope and be deleted (when function ended)
but sounds like data.rnames should have been working.
Well if a copy on creation time works for you, its a wrap :)