Changing a Qt AbstractListModel without using in-place editing - c++

Question

I currently have a QtAbstractListModel subcliass (shortened for clarity):
class HolidayTask;
class HolidayTaskModel: public QAbstractListModel
{
Q_OBJECT
public:
explicit HolidayTaskModel(QObject *parent = 0);
~HolidayTaskModel();
int rowCount(const QModelIndex& parent = QModelIndex()) const;
QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const;
Qt::ItemFlags flags(const QModelIndex& index) const;
bool insertRows(int row, int count, const QModelIndex& parent = QModelIndex());
bool removeRows(int row, int count, const QModelIndex& parent = QModelIndex());
bool setData(const QModelIndex& index, const QVariant& value,
int role = Qt::EditRole);
private:
QVector<HolidayTask*> m_items;
};
Where HolidayTask is the items I'm containing. I'm trying to figure out what needs to be reimplemented for this use case:
The model is modifiable, but not with in place editing in the view: another widget (not a *View subclass) will do the editing, outside from the view this model will be shown in;
It needs to implement not only appending (that would be easy) but also inserting and reordering.
In the case of appending, it would be very easy to make an appendTask function that calls beginInsertRows and endInsertRows, however at least inserting and/or removing is not as trivial.
Most of the code examples I've found around deal with in-place editing (createEditor, etc.), which, as I've wrote above, is not what I'm needing. What should I be implementing to modify this model to accomplish this task? Alternatively, are there any code examples that show this modus operandi?

Answer 1

If you don't need to edit your model data using views, you don't need to implement insertRows, removeRows and setData. Instead, you should create your own modifying functions, e.g. add_task(HolidayTask* task), set_task(int row, HolidayTask* task) and remove_task(int row). In these functions you need to change m_items value to reflect data changes. (Besides, your should switch from QVector to QList if you need insertions and deletions from the middle of the list to be fast). Additionally, you should notify views about the changes:
Call beginRemoveRows before removing a row and endRemoveRows after that.
Call beginInsertRows before inserting a row and endInsertRows after that.
Call emit dataChanged(...) after changing data.

Answer 2

Inserting is like appending, just with a row != m_items.size():
void HolidayTaskModel::addTask(HolidayTask* task)
{
const int row = ...find position...
beginInsertRows(QModelIndex(), row, row);
m_items.insert(row, task);
endInsertRows();
}
Remove a task:
void HolidayTaskModel::removeTask(HolidayTask* task)
{
const int row = m_items.indexOf(task);
if (row == -1)
return;
beginRemoveRows(QModelIndex(), row, row);
delete m_items[row]; //only if the item is owned by the model
m_items.remove(row);
endRemoveRows();
}
For reordering, it depends on your exact use case, for moving single items use beginMoveRows()/endMoveRows(), for sorting reimplement sort() or, often easier, leave the items in the base model unsorted and let a QSortFilterProxyModel proxy do the sorting.