TreeView of QFileSystemModel: Remember selection after sorting

maxwell31

The problem seems to be that the selected indices in QItemSelectionModel do not get updated if I do a sorting of my model. But is there really no functionality in QT which takes care of this?

VRonin

connect a slot to QAbstractItemModel::layoutAboutToBeChanged where you access the QItemSelectionModel::selection(), iterate over all the indexes() and save them in a list of QPersistentModelIndexes

Then create another slot to QAbstractItemModel::layoutChanged, clear the current selection, iterate over your saved indexes and re-select them

maxwell31

@VRonin Thank you for your answer. I think you are right, this is probably how it should be done. Now I am wondering about the following: I store the persistent indices in a

  QList<QPersistentModelIndex> _selectedIndices;

I set it via a Q_INVOKABLE function

Q_INVOKABLE void setSelected(QModelIndexList list) {
    _selectedIndices.clear();
    for(int i=0;i<list.count();i++) {
        _selectedIndices.append(QPersistentModelIndex(list[i]));
    }
}

Now I wonder about how to return it to QML so I don't get type problems

maxwell31

Ok, I should simply use a QVariantList instead of a QList<QPersistentModelIndex>. However, when I want to do the selection again in QML:

            for(var item in selectionList) {
                selection.select(item);
            }

I get the following error:

  qrc:/FileSystem.qml:136: Error: Unable to determine callable overload.  Candidates are:
select(QItemSelection,QItemSelectionModel::SelectionFlags)
select(QModelIndex,QItemSelectionModel::SelectionFlags)

Why does it not recognice that the QVariant holds a QModelindex? But maybe I should do it all on the c++ side. However, I wonder how I get the QItemSelectionModel in my model, or how I can connect the QFileSystemModel and the QItemSelectionModel.

JonB

@maxwell31
Assuming QML compiler is no different than a prog lang compiler like C++, why should it? Each item in a QVariantList is a QVariant. They don't do code analysis :) You will need one of the cast<> constructs, or similar, I presume.

maxwell31

@JonB: Do you know how this can be done in QML? (I am calling the method from QML).

maxwell31

Hm, actually yes, I can use the conversion functions from QVariant.

Regarding my above error: The problem was I did not supply ItemSelectionModel.Select as the second argument

maxwell31

@VRonin : You suggested I should access QItemSelectionModel in c++, how can this be done, if the QItemSelectionModel has only been attached to the view and not the model?

VRonin

@maxwell31 I was thinking of something like:

class SelectionSaver : public QObject
Q_OBJECT
Q_DISABLE_COPY(SelectionSaver)
public:
explicit SelectionSaver(QObject* parent = nullptr) : QObject(parent){}
private:
QVector<QPersistentModelIndex> m_indexList;
public Q_SLOTS:
void storeSelection(const QModelIndexList& sel){
m_indexList.clear();
m_indexList.reserve(sel.size());
for(auto&& idx : sel)
m_indexList.append(idx);
}
void restoreSelection(QItemSelectionModel* selModel){
QItemSelection newSelection;
for(auto&& idx : qAsConst(m_indexList))
newSelection.select(idx,idx);
selModel->select(newSelection,QItemSelectionModel::ClearAndSelect);
m_indexList.clear();
}
};

Then from QML you call storeSelection passing TreeView.selection. selectedIndexes and then call restoreSelection passing TreeView.selection

maxwell31

@VRonin Thanks a lot! I did not now that one can simply pass pointers of the objects from QML. However, for some reason it is not working yet. I will report on this tomorrow.

maxwell31

Yes, it works now. However, in restoreSelection you need to do

          selModel->clearSelection();

before selModel->select. Not sure why, but otherwise the new selection is not shown.