Unhandled Exception

[dougbroadwell]

(Reposted with code inserted)

Windows, Qt Creator 1.0.0, Qt 4.5.0

I'm creating a little SQL input form. In the main window constructor, I create a QSqlTableModel and when I try to associate it with a QTableView created in QDesigner I get the runtime error:

Unhandled exception at 0x00f8a5be in Forecast1.exe: 0xC0000005: Access violation reading location 0x00000004

The arrow in the following code is where it is occurring.

void MainWindow::SetupHeaderWidget()
{
    // Set up the ForecastHeader (database) table Model //
 
    HeaderModel = new QSqlTableModel(this);
    HeaderModel->setTable("ForecastHeader");
    HeaderModel->setSort      (Head_ForecastDate_Col,    Qt::AscendingOrder);
    HeaderModel->setHeaderData(Head_Agency_Col,          Qt::Horizontal, "Agency");
    HeaderModel->setHeaderData(Head_ForecastDate_Col,    Qt::Horizontal, "Forecast Date");
    HeaderModel->setHeaderData(Head_ForecastPercent_Col, Qt::Horizontal, "Percent");
    HeaderModel->setHeaderData(Head_Note_Col,            Qt::Horizontal, "Note");
    HeaderModel->select();                      // Suck the data into this model.
 
    // Set up the ForecastHeader (database) table View //
 
--> tvForecastHeader->setModel(HeaderModel);
    tvForecastHeader->setSelectionMode(QAbstractItemView::SingleSelection);
    ...

void MainWindow::SetupHeaderWidget()
{
    // Set up the ForecastHeader (database) table Model //

    HeaderModel = new QSqlTableModel(this);
    HeaderModel->setTable("ForecastHeader");
    HeaderModel->setSort      (Head_ForecastDate_Col,    Qt::AscendingOrder);
    HeaderModel->setHeaderData(Head_Agency_Col,          Qt::Horizontal, "Agency");
    HeaderModel->setHeaderData(Head_ForecastDate_Col,    Qt::Horizontal, "Forecast Date");
    HeaderModel->setHeaderData(Head_ForecastPercent_Col, Qt::Horizontal, "Percent");
    HeaderModel->setHeaderData(Head_Note_Col,            Qt::Horizontal, "Note");
    HeaderModel->select();                      // Suck the data into this model.

    // Set up the ForecastHeader (database) table View //

--> tvForecastHeader->setModel(HeaderModel);
    tvForecastHeader->setSelectionMode(QAbstractItemView::SingleSelection);
    ...

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In running in the debugger traces it to the lines below, at (in qwidget.h line 144):

QWidgetPrivate *pd = parent->d_func();

is where it happens, when I step a message displayed is: ' stopped: "signal received" ' and the debugger will not go beyond the "Q_DECLARE_PRIVATE(QWidget)" line in the last section.

void QWidget::releaseDC(HDC hdc) const
{
    Q_D(const QWidget);
    // If its the widgets own dc, it will be released elsewhere. If
    // its a different HDC we release it and issue a warning if it
    // fails.
--> if (hdc != d->hd && !ReleaseDC(winId(), hdc))
        qErrnoWarning("QWidget::releaseDC(): failed to release HDC");
    }
    #else
        ...
 
 
WId QWidget::winId() const
{
    if (!testAttribute(Qt::WA_WState_Created) || !internalWinId()) {
        QWidget *that = const_cast<QWidget*>(this);
        that->setAttribute(Qt::WA_NativeWindow);
-->     that->d_func()->createWinId();
        return that->data->winid;
    }
    return data->winid;
}
 
 
void QWidgetPrivate::createWinId(WId winid)
{
    Q_Q(QWidget);
    const bool forceNativeWindow = q->testAttribute(Qt::WA_NativeWindow);
    if (!q->testAttribute(Qt::WA_WState_Created) || (forceNativeWindow && !q->internalWinId())) {
        if (!q->isWindow()) {
            QWidget *parent = q->parentWidget();
-->         QWidgetPrivate *pd = parent->d_func();
            if (forceNativeWindow && !q->testAttribute(Qt::WA_DontCreateNativeAncestors))
                parent->setAttribute(Qt::WA_NativeWindow); 
                ...
 
 
class Q_GUI_EXPORT QWidget : public QObject, public QPaintDevice
{
    Q_OBJECT
--> Q_DECLARE_PRIVATE(QWidget)
    Q_PROPERTY(bool modal READ isModal)
    Q_PROPERTY(Qt::WindowModality windowModality READ windowModality WRITE setWindowModality)
    Q_PROPERTY(bool enabled READ isEnabled WRITE setEnabled)

void QWidget::releaseDC(HDC hdc) const
{
    Q_D(const QWidget);
    // If its the widgets own dc, it will be released elsewhere. If
    // its a different HDC we release it and issue a warning if it
    // fails.
--> if (hdc != d->hd && !ReleaseDC(winId(), hdc))
        qErrnoWarning("QWidget::releaseDC(): failed to release HDC");
    }
    #else
        ...


WId QWidget::winId() const
{
    if (!testAttribute(Qt::WA_WState_Created) || !internalWinId()) {
        QWidget *that = const_cast<QWidget*>(this);
        that->setAttribute(Qt::WA_NativeWindow);
-->     that->d_func()->createWinId();
        return that->data->winid;
    }
    return data->winid;
}


void QWidgetPrivate::createWinId(WId winid)
{
    Q_Q(QWidget);
    const bool forceNativeWindow = q->testAttribute(Qt::WA_NativeWindow);
    if (!q->testAttribute(Qt::WA_WState_Created) || (forceNativeWindow && !q->internalWinId())) {
        if (!q->isWindow()) {
            QWidget *parent = q->parentWidget();
-->         QWidgetPrivate *pd = parent->d_func();
            if (forceNativeWindow && !q->testAttribute(Qt::WA_DontCreateNativeAncestors))
                parent->setAttribute(Qt::WA_NativeWindow); 
                ...


class Q_GUI_EXPORT QWidget : public QObject, public QPaintDevice
{
    Q_OBJECT
--> Q_DECLARE_PRIVATE(QWidget)
    Q_PROPERTY(bool modal READ isModal)
    Q_PROPERTY(Qt::WindowModality windowModality READ windowModality WRITE setWindowModality)
    Q_PROPERTY(bool enabled READ isEnabled WRITE setEnabled)

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Thanks,
Doug

[dougbroadwell]

Another Datapoint:

I'm using multiple inheritance to use graphic objects generated from QDesigner, in this case in the file ui_mainwindow.h (I have used the multiple inheritance approach in other projects without experiencing this problem). If I replace the:

tvForecastHeader->setModel(HeaderModel);

tvForecastHeader->setModel(HeaderModel);

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where tvForecastHeader is created in the object defined in ui_mainwindow.h and instantiated in the mainwindow constructor:

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindowClass)
{
    ui->setupUi(this);
...

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindowClass)
{
    ui->setupUi(this);
...

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with a locally created one as in:

DetailView = new QTableView();
DetailView->setModel(HeaderModel);

DetailView = new QTableView();
DetailView->setModel(HeaderModel);

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It doesn't crash. But I can't see what's different from this and the instatiation in MainWindowObject.

?? Doug

[dougbroadwell]

Well, I switched from using the Multiple Inheritance method to the Single Inheritance method and now it works !?!?!

So I'll consider this a fix for now but would sure like to know if I was doing something wrong or if it was a bug.

Regards,
Doug