closeEditor() not always closing QLineEdit

[mclark]

While using my custom QItemDelegate, the QLineEdit editor is not always closing. The closeEditor() signal is emitted but the QLineEdit object remains in the QTableWidgetItem.

I am using 4.2.2 and setting the edit triggers using QAbstractItemView::AllEditTriggers.

This happens when I have multiple rows in the table and I click (speed is irrelevant) on the editable items:

• Click on row 0, column 1
• Click on row 1, column 1
• Click on row 2, column 1
• repeat

Eventually one of the editors in column 1 will get stuck on, even though the closeEditor() signal was emitted. The qDebug() statement shows the contents of the item where the editor should be closed and is displayed even when the editor does not go away. This state does not allow any other editors to appear in the table, effectively stopping the user from editing any other items.

Has anyone else seen this type of behavior? Any ideas how to prevent this?

class DMXTableCellDelegate : public QItemDelegate
{
    Q_OBJECT
 
public:
    DMXTableCellDelegate( QObject* parent = 0 ) : QItemDelegate( parent )
    { m_parent = parent; }
 
    QWidget* createEditor( QWidget* parent, const QStyleOptionViewItem& option,
                           const QModelIndex& index ) const;
 
private slots:
    void commitAndCloseEditor( void );
 
private:
    QObject* m_parent;
 
};
 
QWidget* DMXTableCellDelegate::createEditor( QWidget* parent,
                                             const QStyleOptionViewItem& option,
                                             const QModelIndex& index ) const
{
    if ( index.column() == COL_Name )
    {
        QLineEdit* lineEdit = new QLineEdit( parent );
        lineEdit->setMaxLength( DEVICE_NAME_MAX );
 
        connect( lineEdit, SIGNAL( returnPressed() ),
                 this, SLOT( commitAndCloseEditor() ) );
        connect( lineEdit, SIGNAL( editingFinished() ),
                 this, SLOT( commitAndCloseEditor() ) );
 
        return lineEdit;
    }
    else
        return QItemDelegate::createEditor( parent, option, index );
}
 
void DMXTableCellDelegate::commitAndCloseEditor( void )
{
    QLineEdit* editor = qobject_cast<QLineEdit*>( sender() );
    emit commitData( editor );
    qDebug( "emit closeEditor(): %s", editor->text().toAscii().data() );
    emit closeEditor( editor, QAbstractItemDelegate::EditNextItem );
}

class DMXTableCellDelegate : public QItemDelegate
{
    Q_OBJECT

public:
    DMXTableCellDelegate( QObject* parent = 0 ) : QItemDelegate( parent )
    { m_parent = parent; }

    QWidget* createEditor( QWidget* parent, const QStyleOptionViewItem& option,
                           const QModelIndex& index ) const;

private slots:
    void commitAndCloseEditor( void );

private:
    QObject* m_parent;

};

QWidget* DMXTableCellDelegate::createEditor( QWidget* parent,
                                             const QStyleOptionViewItem& option,
                                             const QModelIndex& index ) const
{
    if ( index.column() == COL_Name )
    {
        QLineEdit* lineEdit = new QLineEdit( parent );
        lineEdit->setMaxLength( DEVICE_NAME_MAX );

        connect( lineEdit, SIGNAL( returnPressed() ),
                 this, SLOT( commitAndCloseEditor() ) );
        connect( lineEdit, SIGNAL( editingFinished() ),
                 this, SLOT( commitAndCloseEditor() ) );

        return lineEdit;
    }
    else
        return QItemDelegate::createEditor( parent, option, index );
}

void DMXTableCellDelegate::commitAndCloseEditor( void )
{
    QLineEdit* editor = qobject_cast<QLineEdit*>( sender() );
    emit commitData( editor );
    qDebug( "emit closeEditor(): %s", editor->text().toAscii().data() );
    emit closeEditor( editor, QAbstractItemDelegate::EditNextItem );
}

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[wysota]

Are you sure you should emit the signal yourself? I'm not sure the signal is meant to be used this way. From what I see you should reimplement QAbstractItemDelegate::setModelData() instead.

[mclark]

Are you sure you should emit the signal yourself? I'm not sure the signal is meant to be used this way. From what I see you should reimplement QAbstractItemDelegate::setModelData() instead.

I believe I'm safe using the code this way because I took it directly from an example in the C++ GUI Programming With Qt 4 book (Chap. 10 Implementing Custom Delegates).

[mclark]

I added the following connection to verify that the QLineEdit object was not being destroyed by the delegate:

connect( lineEdit, SIGNAL( destroyed( QObject* ) ),
         this, SLOT( DEBUG_destroyed( QObject* ) ) );
 
. . .
 
void DMXTableCellDelegate::DEBUG_destroyed( QObject* obj )
{
    qDebug( "destroyed() - 0x%x", obj );
}

connect( lineEdit, SIGNAL( destroyed( QObject* ) ),
         this, SLOT( DEBUG_destroyed( QObject* ) ) );

. . .

void DMXTableCellDelegate::DEBUG_destroyed( QObject* obj )
{
    qDebug( "destroyed() - 0x%x", obj );
}

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The output result was:

emit closeEditor( 0x17118b8 ): Larry Fist
destroyed() - 0x17118b8
emit closeEditor( 0x1716900 ): Thing 2
destroyed() - 0x1716900
emit closeEditor( 0x1706258 ): Thing 1

The destroyed() signals were received by my delegate for each focus change until the last when no destroyed() signal was received. At this point the editor was still active while focus was on another item.

UPDATE:
I placed a qDebug() call in the createEditor() and what I noticed, for 3 table rows, as I slowly clicked through each column 1 item, was that editor objects were created at only two memory locations. As soon as a third memory location was used the editor froze. A closeEditor() was emitted but no destroyed() signal was received. Could this be a clue?

[wysota]

I think your connect statements are incorrect. editingFinished() is emited when return is pressed, so there is no need to connect to returnPressed as well... Maybe that's your problem? Lose one of those connect statements and see if the situation improves.

[mclark]

Lose one of those connect statements and see if the situation improves.

Thanks wysota, you are partially right. By removing the returnPressed() connection other items can now be edited when an editor in an item gets stuck 'on'. But, I still get an editor stuck 'on', the delegate never gets sent the destroyed() signal.

[wysota]

Maybe there is a bug in your version of Qt? Upgrade might fix the problem. Or at least search the task-tracker to see if a similar issue was reported.

[mclark]

Thanks again wysota, I'm putting together a 'simple' application to test my thought that this may be a bug in Qt 4.2.2. I may have to update to 4.3... If I find a solution I'll post it here.

[wysota]

As I said, check the task-tracker. It might save you a lot of time and effort.