Data store children and Model (QAbstractItemModel subclass) synchronization

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Hi everybody and thanks for reading.

I'm working with QAbstractItemModel and QTreeView, and I need some advices to achieve a correct design.

I've been reading the docs and I'm trying to follow this note: http://developer.qt.nokia.com/doc/qt-4.7/model-view-programming.html#note-13 .

I need to represent different instances of some data in a view (with children). I have a collection with the base for the elements. Each instance (row) can have modified values of the base element

@class RosterElement {
friend class RosterModel;
friend class Roster;
public:
RosterElement(RosterElement *_parent = 0);
virtual ~RosterElement();

int childCount() const;
int row() const;
RosterElement* child(int index) const;
RosterElement* parent() const;

void addChild(RosterElement *child);
void removeChild(RosterElement *child);

QString name;
QString key;
uint cost;
uint size;

protected:
RosterElement(short _type, RosterElement *_parent = 0);

private:
const short type;

RosterElement *parentItem;
QList<RosterElement*> children;

};

class RosterModel : public QAbstractItemModel
{
Q_OBJECT

friend class Roster;

public:
RosterModel(QList<RosterElement*> *_list, ColumnHeader *_header, QObject *parent = 0);

QVariant data(const QModelIndex &index, int role) const;
Qt::ItemFlags flags(const QModelIndex &index) const;
QVariant headerData(int section, Qt::Orientation orientation,
                    int role = Qt::DisplayRole) const;
int rowCount(const QModelIndex &parent = QModelIndex()) const;
int columnCount(const QModelIndex &parent = QModelIndex()) const;
QModelIndex index(int row, int column,
                  const QModelIndex &parent = QModelIndex()) const;
QModelIndex parent(const QModelIndex &index) const;

void emitDataChanged(const QModelIndex& topLeft, const QModelIndex& bottomRight);

signals:

public slots:
void onColumnAboutToBeInserted();
void onColumnInserted();
void onColumnsAboutToBeCleared();
void onColumnsCleared();

private:
QList<RosterElement*> *list;
ColumnHeader *header;
};@

Following the advice, I created a class for the actual data store:

@class Roster
{
public:
Roster(ColumnHeader *header);
~Roster();

RosterModel* model();

void addRosterElement(RosterElement *element);
void removeRosterElement(int row);
void clearAll();

int count();
RosterElement* at(int i);
RosterElement* value(int i);

private:
QList<RosterElement*> internalRoster;
RosterModel *rosterModel;
};@

And I use addRosterElement() to add elements to the data store. This model needs to work with children and there is my problem. I need to add/remove children dynamically acording to some checkboxes (per instance), so I should notify the model about it. I can add a method like addChildrenToItem(RosterElement *element) in Roster class, but then I would have to look for the QModelIndex for that row, which means I have to iterate over the whole data store.

So, could you give me an advice about how to achieve this properly?