How do you save and restore the state of QTreeView?

[deleted385]

It does this by default:

Initially, I'd one table TestTable and the QTreeView was expanded. When I added the NewTable, it collapsed. I expanded it again and executed 3 more statements and it collapsed again. Then I expanded some nodes and executed rollback and it collapsed! That, probably, is because I remove all rows and add new nodes. When I execute statement(s), this function is called:

void ObjectsView::onNoSelect(const QString &query){
    bool isDDL = query.toUpper().contains("CREATE") || query.contains("ALTER") || query.contains("DROP");
    if(!isDDL) return;
    this->query->clear();
    this->query->prepare("SELECT * FROM sqlite_master");
    this->query->exec();
    makeTree();
}

and the makeTree removes all rows and add new like this:

void ObjectsView::makeTree()
{
    QStandardItemModel *model;
    if(tree->model()){
        tree->model()->removeRows(0, tree->model()->rowCount());
        model = qobject_cast<QStandardItemModel*>(tree->model());
    }
    else{
        model = new QStandardItemModel(tree);
        model->setColumnCount(2);
        tree->setModel(model);
        tree->header()->setSectionResizeMode(0, QHeaderView::Stretch);
    }
    QStandardItem *rootNode;
    while (query->next()) {
       ...
        auto child = new QStandardItem(text);
        rootNode->appendRow(child);
        ...
    }
    // here in another foreach loop I add nodes in child node.
}

How to save the states of previous tree and apply those states in new tree? Names that are common in both old and new tree, I want those to get the state (expanded/collapsed) from previous tree.

[JonB]

@Emon-Haque
QTreeView, like other widgets, are not amenable to "serializing"/saving. It is normal to save the state of the model it is using, and restore that.

Since I think that, say, the expanded/contracted state is a QTreeView-only thing, not in the model, you would need to traverse the current tree saving whatever for all of those and then re-apply as appropriate to nodes in the new tree.

You can get further information by Googling qtreeview save state. Note e.g. https://forum.qt.io/topic/58592/saving-expanded-state-of-qtreeview/2, where our @Chris-Kawa mentions:

One way to approach the problem would be to keep expansion state as part of your model data under a custom role. You would then implement in your model setData() for that role to store the state and data() to retrieve it and query/apply whenever you need to.

See also https://stackoverflow.com/questions/3253301/howto-restore-qtreeview-last-expanded-state for a more detailed discussion, and perhaps some recursive code which would show you what needs doing/help you.

[deleted385]

@JonB, look at that:

void ObjectsView::makeTree()
{
    QStandardItemModel *model;
    QMap<QString, QStringList*> expanded;
    if(tree->model()){
        for (int row = 0; row < tree->model()->rowCount(); row++) {
            auto index = tree->model()->index(row, 0);
            if(!tree->isExpanded(index)) continue;
            auto node = tree->model()->data(index).toString();
            auto trimmed = node.left(node.indexOf(' '));
            auto list = new QStringList;
            expanded.insert(trimmed, list);
            for (int child = 0; child < tree->model()->rowCount(index); child++) {
                auto childIndex = tree->model()->index(child, 0, index);
                if(!tree->isExpanded(childIndex)) continue;
                node = tree->model()->data(childIndex).toString();
                trimmed = node.left(node.indexOf(' '));
                list->append(trimmed);
            }
        }
        tree->model()->removeRows(0, tree->model()->rowCount());
        model = qobject_cast<QStandardItemModel*>(tree->model());
    }
    ....
    // rest of the code
    ....
    for (int row = 0; row < tree->model()->rowCount(); row++) {
        auto index = tree->model()->index(row, 0);
        auto node = tree->model()->data(index).toString();
        auto trimmed = node.left(node.indexOf(' '));
        if(!expanded.keys().contains(trimmed)) continue;
        tree->setExpanded(index, true);
        if(expanded.value(trimmed)->size()){
            auto list = expanded.value(trimmed);
            for (int child = 0; child < tree->model()->rowCount(index); child++) {
                auto childIndex = tree->model()->index(child, 0, index);
                node = tree->model()->data(childIndex).toString();
                trimmed = node.left(node.indexOf(' '));
                if(list->contains(trimmed)) tree->setExpanded(childIndex, true);
            }
        }
    }
    qDeleteAll(expanded.values());
}

and somehow it works:

Any suggestion for improvement?