Extending QFileSystemModel by a bool variable - qt

Question

I would like to extend the QFileSystemModel. I would like to have a custom role IsSelectedRole where I can store whether a bool value which stores whether a file got selected in a QML TreeView. More precisely, I don't know how to set the setData and data function of my QFileSystemModel derived class, like where to store the data. I guess making my own tree of bool variables should work, but I hope that there is an easier way.

Answer 1

Qt already has a model that stores item selections: QItemSelectionModel. This model is used by the widget views as well as the QML views. All that's left for you to do is to overlay the data from that model on top of the data from QFileSystemModel, in a viewmodel.
You definitely shouldn't be deriving from QFileSystemModel. The viewmodel maintains the state for a single view only, and should be a proxy that overlays your role on top of the underlying model.
The proxy doesn't have to assume anything about the underlying model, and can work on any model, not just the QFileSystemModel.
For example:
// https://github.com/KubaO/stackoverflown/tree/master/questions/filesystem-model-select-50132273
#include <QtWidgets>
#include <algorithm>
class SelectionProxy : public QIdentityProxyModel {
Q_OBJECT
Q_PROPERTY(QItemSelectionModel* selectionModel
READ selectionModel WRITE setSelectionModel NOTIFY selectionModelChanged)
Q_PROPERTY(QVector<int> roles READ roles WRITE setRoles)
using self_t = SelectionProxy;
using base_t = QIdentityProxyModel;
using model_t = QItemSelectionModel;
QPointer<QItemSelectionModel> m_model;
QVector<QMetaObject::Connection> m_modelConnections;
QVector<int> m_roles{IsSelectedRole};
QModelIndex topLeft() const {
return sourceModel()->index(0, 0);
}
QModelIndex bottomRight() const {
return sourceModel()->index(sourceModel()->rowCount()-1, sourceModel()->columnCount()-1);
}
void onSelectionChanged(const QItemSelection &selected, const QItemSelection &deselected) {
auto sel = selected;
sel.merge(deselected, QItemSelectionModel::Select);
for (auto &range : qAsConst(sel)) {
auto topLeft = mapFromSource(range.topLeft());
auto bottomRight = mapFromSource(range.bottomRight());
emit dataChanged(topLeft, bottomRight, m_roles);
}
}
void onModelChanged(QAbstractItemModel *model) {
setSourceModel(model);
}
bool check(const QModelIndex &index, int role) const {
return index.isValid() && m_model && m_roles.contains(role);
}
public:
static constexpr int IsSelectedRole = Qt::UserRole + 44;
SelectionProxy(QObject *parent = {}) : QIdentityProxyModel(parent) {}
QItemSelectionModel *selectionModel() const { return m_model; }
virtual void setSelectionModel(QItemSelectionModel *model) {
if (model == m_model) return;
for (auto &conn : m_modelConnections)
disconnect(conn);
m_model = model;
m_modelConnections = {
connect(m_model, &model_t::selectionChanged, this, &self_t::onSelectionChanged),
connect(m_model, &model_t::modelChanged, this, &self_t::onModelChanged) };
setSourceModel(model->model());
emit selectionModelChanged(m_model);
}
Q_SIGNAL void selectionModelChanged(QItemSelectionModel *);
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override {
if (!check(index, role))
return base_t::data(index, role);
return m_model->isSelected(mapToSource(index));
}
bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override {
if (!check(index, role))
return base_t::setData(index, value, role);
using Sel = QItemSelectionModel;
m_model->select(mapToSource(index), value.toBool() ? Sel::SelectCurrent : (Sel::Deselect | Sel::Current));
return true;
}
QVector<int> roles() const { return m_roles; }
void setRoles(QVector<int> roles) {
std::sort(roles.begin(), roles.end());
if (roles == m_roles)
return;
std::swap(roles, m_roles);
if (!m_model)
return;
QVector<int> allRoles;
std::merge(roles.begin(), roles.end(), m_roles.begin(), m_roles.end(), std::back_inserter(allRoles));
emit dataChanged(topLeft(), bottomRight(), allRoles);
}
void setRole(int role) {
setRoles({role});
}
};
#include "main.moc"
A simple demonstrator sets up two views of the filesystem model; the bottom view shows true/false indicating the selection status of the first view.
int main(int argc, char **argv) {
QApplication app{argc, argv};
QWidget win;
QVBoxLayout layout{&win};
QTreeView left, right;
layout.addWidget(&left);
layout.addWidget(&right);
QFileSystemModel model;
SelectionProxy selProxy;
model.setRootPath(QStandardPaths::writableLocation(QStandardPaths::HomeLocation));
auto rootPathIndex = model.index(model.rootPath());
left.setModel(&model);
left.setSelectionMode(QAbstractItemView::MultiSelection);
left.setRootIndex(rootPathIndex);
selProxy.setRole(Qt::DisplayRole);
selProxy.setSelectionModel(left.selectionModel());
right.setModel(&selProxy);
right.setRootIndex(selProxy.mapFromSource(rootPathIndex));
for (int col : {1,2,3})
right.hideColumn(col);
win.show();
return app.exec();
}