Split a QAbstarctListModel into sub models - qt

Question

I have a list of custom objects that I need to split across multiple pages of a SwipeView.
Right now, I implement a QAbstractListModel to provide the data to my QML view through custom roles.
But when I have more then a given number of object, I need to split my model in multiple chunks that will be displayed on different pages of a SwipeView.
If my model has 20 object, my SwipeView will have 2 pages with 12 Items in the first one and the 8 remainings in the second page for example but the number of items is, of course, dynamic.
I know that I can use a QSortProxyFilter or a DelegateModel to filter my model on a criteria but I don't know how I can use them to create groups usable as submodels for the content of the pages of the SwipeView. Because of course, I cannot just change the filter when the page change because that wouldn't make the items visible when swiping from one page to the other.
Thanks for any hint or idea on how to achieve this.

Answer 1

Why don't you include a model into another model? You can return the model to QML via QVariant::fromValue. See my example:
models.h
class ChildItem{
public:
ChildItem() {}
};
class ChildModel: public QAbstractListModel{
Q_OBJECT
public:
explicit ChildModel(QObject *parent = nullptr);
void addItem(const ChildItem &item);
int rowCount(const QModelIndex &parent = QModelIndex()) const;
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
signals:
void itemAdded();
protected:
QHash<int,QByteArray> roleNames() const;
private:
QVector<ChildItem> m_items;
};
class ModelItem{
public:
ModelItem() {}
ChildModel *childModel() const;
private:
ChildModel *m_childModel;
};
class MainModel: public QAbstractListModel{
Q_OBJECT
public:
explicit MainModel(QObject *parent = nullptr);
void addItem(const ModelItem &item);
int rowCount(const QModelIndex &parent = QModelIndex()) const;
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
signals:
void itemAdded();
protected:
QHash<int,QByteArray> roleNames() const;
private:
QVector<ModelItem> m_items;
};
models.cpp
ChildModel *ModelItem::childModel() const{
return m_childModel;
}
QVariant MainModel::data(const QModelIndex & index, int role) const {
if (index.row() < 0 || index.row() >= (int)m_items.size())
return QVariant();
const MainModel &item = m_items[index.row()];
switch (role) {
case MainModelRoles::ChildModel:{
return QVariant::fromValue(item.childModel());
}
default: {
break;
}
}
return QVariant();
}
QHash<int, QByteArray> MainModel::roleNames() const {
QHash<int, QByteArray> roles;
roles[MainModelRoles::ChildModel] = "child_model";
return roles;
}
From within QML you can present model role name as a new model for another element. For example:
StackLayout which is your main element, includes Repeater.
Repeater model is MainModel class instance.
Repeater delegate includes ListView
ListView takes ChildModel as a model for itself (child_model reference)
So you can contain any amount of different models inside main model and expose them to QML as model property. Is this what you're looking for?