Garbage collector issue QAbstractListModel

[Pierreldff]

Hi ,
i'm working with qt 4.8.

I have my model in c++ and a ListView in Qml.
I set my model in c++ like this

ListModel : public QAbstractListModel
{
    Q_OBJECT
 
public:
	enum ListModelRole
	{
		rName = Qt::UserRole + 1,
		rId = Qt::UserRole + 1,
	};
	ListModel (QObject *parent = 0);
	virtual ~ListModel ();
 
	virtual		void ClearWorklistModel();
	int			rowCount(const QModelIndex & parent = QModelIndex()) const;
	QVariant	data(const QModelIndex & index, int role = Qt::DisplayRole) const;
	void		SetValues( const vector<pair<string, string>> & iValues );
 
protected :
	vector<pair<string, string>> m_values ;
 
};

ListModel : public QAbstractListModel
{
    Q_OBJECT
	
public:
	enum ListModelRole
	{
		rName = Qt::UserRole + 1,
		rId = Qt::UserRole + 1,
	};
	ListModel (QObject *parent = 0);
	virtual ~ListModel ();

	virtual		void ClearWorklistModel();
	int			rowCount(const QModelIndex & parent = QModelIndex()) const;
	QVariant	data(const QModelIndex & index, int role = Qt::DisplayRole) const;
	void		SetValues( const vector<pair<string, string>> & iValues );

protected :
	vector<pair<string, string>> m_values ;

};

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ListModel::ListModel( QObject *pParent/*NULL*/ )
:	QAbstractListModel(pParent)
{
	QHash<int, QByteArray> roles;
	roles[rName				] = "rName";				
	roles[rId				] = "rId";		
	setRoleNames( roles );
}	
int 
ListModel::rowCount( const QModelIndex & parent ) const
{
	return m_values.size();
}
void 
ListModel::ClearWorklistModel()
{
    beginRemoveRows( startRefreshIndex, 0, m_values.size()-1 );
	this->removeRows( 0, m_values.size()-1 );
    endRemoveRows();
	m_values.clear();
}
 
void		
ListModel::SetValues( const vector<pair<string, string>> & iValues )
{
	this->ClearWorklistModel();
	this->beginResetModel();
	m_values = iValues ;
	this->endResetModel();
}
 
QVariant 
ListModel::data( const QModelIndex & index, int role ) const
{
	// check conditions
	if (index.row() < 0 || (size_t)index.row() > m_values.size() )
	{
		return QVariant();
	}
	QVariant value ;
	switch( role )
	{
		case rName :
			value = m_values.at( index.row() ).first.c_str() ;
			break;
		case rId :
			value = m_values.at( index.row() ).second.c_str() ;
			break;
	}
	return value ;
}

ListModel::ListModel( QObject *pParent/*NULL*/ )
:	QAbstractListModel(pParent)
{
	QHash<int, QByteArray> roles;
	roles[rName				] = "rName";				
	roles[rId				] = "rId";		
	setRoleNames( roles );
}	
int 
ListModel::rowCount( const QModelIndex & parent ) const
{
	return m_values.size();
}
void 
ListModel::ClearWorklistModel()
{
    beginRemoveRows( startRefreshIndex, 0, m_values.size()-1 );
	this->removeRows( 0, m_values.size()-1 );
    endRemoveRows();
	m_values.clear();
}

void		
ListModel::SetValues( const vector<pair<string, string>> & iValues )
{
	this->ClearWorklistModel();
	this->beginResetModel();
	m_values = iValues ;
	this->endResetModel();
}

QVariant 
ListModel::data( const QModelIndex & index, int role ) const
{
	// check conditions
	if (index.row() < 0 || (size_t)index.row() > m_values.size() )
	{
		return QVariant();
	}
	QVariant value ;
	switch( role )
	{
		case rName :
			value = m_values.at( index.row() ).first.c_str() ;
			break;
		case rId :
			value = m_values.at( index.row() ).second.c_str() ;
			break;
	}
	return value ;
}

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and my ListView

ListView
{
    id : myListView
    objectName : "myWorklistView"
 
    model: myModel
    delegate: Item
    {
		Text
		{
			test : rName + " _ " + rId 
		}
		Image
		{
			source: "ClientThumbnail.png"
		}
	}
}

ListView
{
    id : myListView
    objectName : "myWorklistView"

    model: myModel
    delegate: Item
    {
		Text
		{
			test : rName + " _ " + rId 
		}
		Image
		{
			source: "ClientThumbnail.png"
		}
	}
}

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So in my program i create a QDeclarativeView and then i set the model like

QDeclarativeView *pDeclarativeListView = new QDeclarativeView( QUrl("myqmlFile.qml") );
QDeclarativeContext * pDeclarativeCtxt = pDeclarativeListView->rootContext();
pDeclarativeCtxt->setContextProperty( "myModel", &currentWorkListModel );

QDeclarativeView *pDeclarativeListView = new QDeclarativeView( QUrl("myqmlFile.qml") );
QDeclarativeContext * pDeclarativeCtxt = pDeclarativeListView->rootContext();
pDeclarativeCtxt->setContextProperty( "myModel", &currentWorkListModel );

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At last i want to refresh my ListView i call SetValues but each time i set new Values i have some memory consumption. I notice when i delete my DeclarativeView the memory consumption is fine.

I imagine there is some Garbage Collector in QML that handle QDeclarativeItems created but how can I tell to QML that i want that items which are no longer available in my ListView have to be deleted.

Thanks in advance

Pierre

[Pierreldff]

Ok i found how to say to delete the clean up items. I have to tell to the QApplication to Delete Deferred Items so i send post message to the app.

[wysota]

The items will be deleted automatically when the time comes, no need to do anything.

[anda_skoa]

also: your SetValues needless calls ClearWorkListModel(), it resets anyway.

Your ClearWorkListModel() could also just do a reset.

Cheers,
_

[Pierreldff]

Ok,
but the issue was that i could fill up my model for instance an hundread time, and then the program crash because items were not deleted and program can't allocate more memory. With calling this QCoreApplication::sendPostedEvents(0, QEvent:eferredDelete);, i do not have this issue anymore. My memory is fine.

Thank you for your time

[wysota]

Deferred delete happens automatically whenever the application processes its events so there should be no need for such calls. If you do require it, then it means something related to event processing in your application is seriously broken. Are you calling QApplication::exec() in your main function?

[Pierreldff]

Effectively the event processing seems to be broken... Because in some case my items are well deleted. Exec is effectively called.

[wysota]

Are you blocking the event loop in any way? Do you have some long running while or for loop somewhere in your code related to using the model?