Why my application is collapsed?

[Robert_is_not_robot]

Hi guys!
I am a freshman for Qt.
Now I want a table to display formulas. There are 4 columns in table. The first column is a QCheckbox. And the others contain a QComboBox. I use a class derived from QStyledItemDelegate and a class derived from QAbstractTableModel to build it. The code of these class is following:

class FormulaListModel : public QAbstractTableModel
{
	typedef struct
	{
		QString op1_name;
		QString op2_name;
		QString op;
		bool isEnable;
	}FORMULA, *PFORMULA;
	Q_OBJECT

public:
	FormulaListModel(QObject *parent);
	~FormulaListModel();

	/*Implement the necessary virtual function of QAbstractListModel*/
	int rowCount(const QModelIndex & parent = QModelIndex()) const;
	int columnCount(const QModelIndex & parent = QModelIndex()) const;
	QVariant data(const QModelIndex & index, int role = Qt::DisplayRole) const;
private:
	QVector<PFORMULA> m_lsFormula;
};
FormulaListModel::FormulaListModel(QObject *parent)
	: QAbstractTableModel(parent)
{
	int i;
	for (i = 0;i < 10;i ++)
	{
		PFORMULA formula = new FORMULA;
		formula->isEnable = true;
		formula->op = "+";
		formula->op1_name = QString("%1").arg(i);
		formula->op2_name = QString("%1").arg(50 - i);
		m_lsFormula.append(formula);
	}
}

FormulaListModel::~FormulaListModel()
{
	foreach(PFORMULA f, m_lsFormula)
	{
		if (f)
		{
			delete f;
		}
	}
	m_lsFormula.clear();
}
int FormulaListModel::rowCount(const QModelIndex & parent) const
{
	return m_lsFormula.count();
}
int FormulaListModel::columnCount(const QModelIndex & parent) const
{
	return 4;
}
QVariant FormulaListModel::data(const QModelIndex & index, int role) const
{
	switch(role)
	{
	case Qt::EditRole:
		{
			int r = index.row();
			int c = index.column();
			PFORMULA pf = m_lsFormula[r];
			switch(c)
			{
			case 0:
				return pf->isEnable;
			case 1:
				return pf->op1_name;
			case 2:
				return pf->op;
			case 3:
				return pf->op2_name;
			}
		}
	case Qt::DisplayRole:
		{
			int c = index.column();
			int r = index.row();
			PFORMULA pf = m_lsFormula[r];
			QStringList lsStr;

			switch(c)
			{
			case 0:
				return "IsUsed";
			case 1:
			case 3:
				lsStr << "1";
				lsStr << "2";
				return lsStr;
			case 2:
				lsStr << "+";
				lsStr << "-";
				return lsStr;
			}
		}
	case Qt::DecorationRole:
		{
			QColor clr(Qt::transparent);
			return clr;
		}
	case Qt::SizeHintRole:
		return QSize(130, 16);
	case Qt::FontRole:
		{
			QFont font;
			font.setBold(true);
			return font;
		}
	case Qt::BackgroundRole:
		{
			QBrush brush(Qt::transparent);
			return brush;
		}
	case Qt::TextAlignmentRole:
		{
			return Qt::AlignHCenter;
		}
	case Qt::CheckStateRole:
		{
			return Qt::Checked;
		}
	case Qt::TextColorRole:
		{
			QColor clr(Qt::black);
			return clr;
		}
	case Qt::ToolTipRole:
		{
			return "Formula List";
		}
	}
}
class FormulaItemDelegate : public QStyledItemDelegate
{
	Q_OBJECT

public:
	FormulaItemDelegate(QObject *parent);
	~FormulaItemDelegate();

	QWidget * createEditor(QWidget * parent, const QStyleOptionViewItem & option, 
		const QModelIndex & index)const;
	void setEditorData(QWidget * editor, const QModelIndex & index) const;
	void updateEditorGeometry(QWidget *editor,
                                      const QStyleOptionViewItem &option,
                                      const QModelIndex &index) const;
	void setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const;
	void paint(QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index) const;
private:
	
};
FormulaItemDelegate::FormulaItemDelegate(QObject *parent)
	: QStyledItemDelegate(parent)
{

}

FormulaItemDelegate::~FormulaItemDelegate()
{

}
QWidget * FormulaItemDelegate::createEditor(QWidget * parent, const QStyleOptionViewItem & option, 
	const QModelIndex & index)const
{
	QVariant value = index.model()->data(index, Qt::DisplayRole);

	if (index.column() == 0)
	{
		QCheckBox * pBox = new QCheckBox(parent);
		pBox->setText(value.toString());
		return pBox;
	}
	else
	{
		QComboBox * pBox = new QComboBox(parent);
		pBox->addItems(value.toStringList());
		return pBox;
	}
}
void FormulaItemDelegate::setEditorData(QWidget * editor, const QModelIndex & index) const
{
	QVariant value = index.model()->data(index, Qt::EditRole);

	if (index.column() == 0)
	{
		bool checked = value.toBool();

		QCheckBox * pBox = static_cast<QCheckBox *>(editor);
		if (pBox)
		{
			pBox->setChecked(checked);
		}
	}
	else
	{
		QString str = index.model()->data(index, Qt::EditRole).toString();

		QComboBox * pBox = static_cast<QComboBox *>(editor);
		if (pBox)
		{
			pBox->setCurrentIndex(pBox->findText(str));
		}
	}
}
void FormulaItemDelegate::updateEditorGeometry(QWidget *editor,
                                      const QStyleOptionViewItem &option,
                                      const QModelIndex &index) const
{
	QRect rc = option.rect;
	editor->setGeometry(rc);
}
void FormulaItemDelegate::setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const
{
	if (index.column() == 0)
	{
		QCheckBox * pBox = static_cast<QCheckBox *>(editor);
		pBox->update();
		bool checked = pBox->isChecked();

		model->setData(index, checked, Qt::EditRole);
	}
	else
	{
		QComboBox * pBox = static_cast<QComboBox *>(editor);
		pBox->update();
		QString str = pBox->currentText();

		model->setData(index, str, Qt::EditRole);
	}
}
void FormulaItemDelegate::paint(QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index) const
{
	//画控件本身
	int x = option.rect.x();
	int y = option.rect.y();
	painter->setBackgroundMode(Qt::TransparentMode);
	QVariant value = index.model()->data(index, Qt::DisplayRole);
	if (index.column() == 0)
	{
		bool checked = value.toBool();
		QStyleOptionButton style;
		style.rect = QRect(x, y + 8, 12, 12);
		style.state |= QStyle::State_Enabled;
		style.state |= checked ? QStyle::State_On : QStyle::State_Off;
		QApplication::style()->drawControl(QStyle::CE_CheckBox, &style, painter);
	}
	else
	{
		QStyleOptionComplex style;
		style.rect = QRect(x, y + 8, 12, 12);
		style.state = QStyle::State_HasFocus;
		style.state |= QStyle::State_Enabled;
		QApplication::style()->drawComplexControl(QStyle::CC_ComboBox, &style, painter);
	}
}

Then I use the following code to make table:

	m_plsModel = new FormulaListModel(this);
	ui.tvFormulas->setModel(m_plsModel);
	ui.tvFormulas->setShowGrid(false);
	QHeaderView * pHeader = ui.tvFormulas->horizontalHeader();
	pHeader->hide();
	pHeader = ui.tvFormulas->verticalHeader();
	pHeader->hide();
	//列宽
	ui.tvFormulas->setColumnWidth(0, 80);
	ui.tvFormulas->setColumnWidth(1, 150);
	ui.tvFormulas->setColumnWidth(2, 150);
	ui.tvFormulas->setColumnWidth(3, 150);
	m_pFormulaItem = new FormulaItemDelegate(this);
	ui.tvFormulas->setItemDelegate(m_pFormulaItem);

	for (int i = 0;i < m_plsModel->rowCount();i ++)
	{
		for (int j = 0;j < m_plsModel->columnCount();j ++)
		{
			ui.tvFormulas->openPersistentEditor(m_plsModel->index(i, j));
		}
	}
	ui.tvFormulas->updateGeometry();

It's bizarre that when I use these code in a simple testing project, they works perfect. But when I use the same code in my real project, it collapsed when I use mouse wheel to scroll it. I check the code again and again. They are same as each other. The only difference is the environment. My test project is a QDialog application, though my real project is a QMainWindow application. The table is showed in a QDialog poped up. Is this the reason of collapse?
I hope someone could be kind to help me. Thank you!

[Robert_is_not_robot]

This bug had been fixed. The resolve is to add protected function in delegate class named eventFilter. In this member function, QEvent::Wheel should be filtered for QCheckBox because it can't support it. So, bug of collapse is fixed.