QItemDelegate Editor Crash

[mclark]

All the problems I'm having are related to the QWidget* parameter in the QMessageBox() call that I'm using to warn the user. If I comment out only the QMessageBox call I do not get another call to setModelData(), nor do I get a crash.

These will cause the crash in setModelData():

QMessageBox::warning( editor,
                      "Message Title",
                      "Message String",
                      QMessageBox::Ok, QMessageBox::NoButton );
 
QMessageBox::warning( qobject_cast<QWidget*>( m_parent ),
                      "Message Title",
                      "Message String",
                      QMessageBox::Ok, QMessageBox::NoButton );

QMessageBox::warning( editor,
                      "Message Title",
                      "Message String",
                      QMessageBox::Ok, QMessageBox::NoButton );

QMessageBox::warning( qobject_cast<QWidget*>( m_parent ),
                      "Message Title",
                      "Message String",
                      QMessageBox::Ok, QMessageBox::NoButton );

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Is the problem that I cannot call QMessageBox from within the setModelData() function?

If this is NOT the problem, what QWidget* pointer should I be using when I call QMessageBox? The above examples use the QWidget* editor parameter and the delegate owners pointer. What else could I use here?

[wysota]

In general you shouldn't do that because setModelData can be called without the editor. If you really need such a mechanism, use a custom event or something like that to trigger the message box after the new data is already in the model and the flow returns to the event loop.

[mclark]

I am unfamiliar with customEvent. Since I already have an event filter for my base Table class, can I use it to receive the custom events?

I'm posting custom events from my setModelData() function but they are never received by my customEvent() handler. Clearly I'm misunderstanding how I need to connect these together. Any suggestions?

These are my class definitions:

class TableEvent : public QEvent
{
public:
    TableEvent( Type type, const QString& sOrigValue ) : QEvent( type )
    {
        m_sOrigValue = sOrigValue;
    }
 
public:
    QString    m_sOrigValue;
 
};
 
 
class TableKeyHandler : public QObject
{
    Q_OBJECT
 
public:
    TableKeyHandler( Table* parent = 0 ) { m_pParent = parent; }
 
protected:
    bool eventFilter( QObject* obj, QEvent* pEvent );
    void customEvent( TableEvent* pEvent );
 
private:
    Table* m_pParent;
 
};

class TableEvent : public QEvent
{
public:
    TableEvent( Type type, const QString& sOrigValue ) : QEvent( type )
    {
        m_sOrigValue = sOrigValue;
    }

public:
    QString    m_sOrigValue;

};


class TableKeyHandler : public QObject
{
    Q_OBJECT

public:
    TableKeyHandler( Table* parent = 0 ) { m_pParent = parent; }

protected:
    bool eventFilter( QObject* obj, QEvent* pEvent );
    void customEvent( TableEvent* pEvent );

private:
    Table* m_pParent;

};

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And this is how I'm attempting to process events?

bool TableKeyHandler::eventFilter( QObject* obj, QEvent* pEvent )
{
    if ( pEvent->type() == QEvent::KeyPress )
    {
        QKeyEvent* pKeyEvent = static_cast<QKeyEvent*>( pEvent );
        int nKey = pKeyEvent->key();
        . . .
    }
}
 
 
void TableCellKeyHandler::customEvent( TableEvent* pEvent )
{
    TableEvent* pTableEvent = static_cast<TableEvent*>( pEvent );
 
    if ( pEvent->type() == EVENT_NAME_CHANGE )
    {
        // do validation of Name here
        pEvent->accept();
    }
    else
 
        pEvent->ignore();
}

bool TableKeyHandler::eventFilter( QObject* obj, QEvent* pEvent )
{
    if ( pEvent->type() == QEvent::KeyPress )
    {
        QKeyEvent* pKeyEvent = static_cast<QKeyEvent*>( pEvent );
        int nKey = pKeyEvent->key();
        . . .
    }
}


void TableCellKeyHandler::customEvent( TableEvent* pEvent )
{
    TableEvent* pTableEvent = static_cast<TableEvent*>( pEvent );

    if ( pEvent->type() == EVENT_NAME_CHANGE )
    {
        // do validation of Name here
        pEvent->accept();
    }
    else

        pEvent->ignore();
}

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And this is how I'm attempting to post a custom event:

void DMXTableCellDelegate::setModelData( QWidget* editor, QAbstractItemModel* model,
                                         const QModelIndex& index ) const
{
    if ( index.column() == COL_Name )
    {
        QLineEdit* lineEdit = qobject_cast<QLineEdit*>( editor );
 
        // Validate the Name string
        if ( (lineEdit != NULL) || !lineEdit->text().isEmpty() )
        {
            QString sOrigName = index.data( Qt::EditRole ).toString();
            TableEvent* pEvent = new TableEvent( EVENT_NAME_CHANGE, sOrigName );
            QObject* pObj = qobject_cast<QObject*>(m_parent);
            static_cast<DMXTable*>( m_parent )->m_parent->m_pApp->postEvent( pObj, pEvent );
        }
    }
    . . .
}

void DMXTableCellDelegate::setModelData( QWidget* editor, QAbstractItemModel* model,
                                         const QModelIndex& index ) const
{
    if ( index.column() == COL_Name )
    {
        QLineEdit* lineEdit = qobject_cast<QLineEdit*>( editor );

        // Validate the Name string
        if ( (lineEdit != NULL) || !lineEdit->text().isEmpty() )
        {
            QString sOrigName = index.data( Qt::EditRole ).toString();
            TableEvent* pEvent = new TableEvent( EVENT_NAME_CHANGE, sOrigName );
            QObject* pObj = qobject_cast<QObject*>(m_parent);
            static_cast<DMXTable*>( m_parent )->m_parent->m_pApp->postEvent( pObj, pEvent );
        }
    }
    . . .
}

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[edice]

Hello there!

I know this is an ancient thread, but don't you hate it when a thread is full of questions and not answers?

I have seen a crash similar to what you describe, but might not be exactly the same.
The problem is due to the QMessageBox holding up the commit sequence, AND the model being reset at the same time.

When you call QMessageBox::warning(), it will NOT return from the warning() call until the user has pressed OK on the warning box that appears.

To make this happen, QMessageBox runs its own QT-event-processor loop within ::warning(), and that processes the gui drawing calls (to make the dialog appear and be interactive) AS WELL AS distributes and processes other events in the system.

In my case, one of those posted events was updating the data in the table,
which called model->reset(),
which reset the editor,
which called editor->deleteLater(),
and then the DeleteLater event was processed, my editor was deleted.
The trap is set.

When the OK in QMessageBox is pressed, delegate->setModelData() can finally return.
The very next call (in qabstractitemview.cpp) is editor->installEventFilter().
So it calls a method on a stale and invalid pointer. FAIL.

So my solution was to avoid opening a QMessageBox during setModelData().
Instead, if there are error messages to display, I post a message to the tableview / dialog / something else
and they can display the error message.

Takeaway message: setModelData() should not start a new event loop.