KViewStateSerializer Class

Detailed Description

Implement the indexFromConfigString and indexToConfigString methods to handle the model in the view whose state is being saved. These implementations can be quite trivial:

QModelIndex DynamicTreeStateSaver::indexFromConfigString(const QAbstractItemModel* model,
                                                         const QString& key) const
{
    QModelIndexList list = model->match(model->index(0, 0),
                                        DynamicTreeModel::DynamicTreeModelId,
                                        key.toInt(), 1, Qt::MatchRecursive);
    if (list.isEmpty()) {
        return QModelIndex();
    }
    return list.first();
}

QString DynamicTreeStateSaver::indexToConfigString(const QModelIndex& index) const
{
    return index.data(DynamicTreeModel::DynamicTreeModelId).toString();
}

It is possible to restore the state of a QTreeView (that is, the expanded state and selected state of all indexes as well as the horizontal and vertical scroll state) by using setView.

If there is no tree view state to restore (for example if using QML), the selection state of a QItemSelectionModel can be saved or restored instead.

The state of any QAbstractScrollArea can also be saved and restored.

A KViewStateSerializer should be created on the stack when saving and on the heap when restoring. The model may be populated dynamically between several event loops, so it may not be immediate for the indexes that should be selected to be in the model. The saver should *not* be persisted as a member. The saver will destroy itself when it has completed the restoration specified in the config group, or a small amount of time has elapsed.

MyWidget::MyWidget(Qobject *parent)
  : QWidget(parent)
{
    ...

    m_view = new QTreeView(splitter);
    m_view->setModel(model);

    connect(model, &QAbstractItemModel::modelAboutToBeReset, this, [this]() { saveState(); });
    connect(model, &QAbstractItemModel::modelReset, [this]() { restoreState(); });
    connect(qApp, &QApplication::aboutToQuit, this, [this]() { saveState(); });

    restoreState();
}

void StateSaverWidget::saveState()
{
    ConcreteStateSaver saver;
    saver.setView(m_view);

    KConfigGroup cfg(KSharedConfig::openConfig(), "ExampleViewState");
    saver.saveState(cfg);
    cfg.sync();
}

void StateSaverWidget::restoreState()
{
    // Will delete itself.
    ConcreteTreeStateSaver *saver = new ConcreteStateSaver();
    saver->setView(m_view);
    KConfigGroup cfg(KSharedConfig::openConfig(), "ExampleViewState");
    saver->restoreState(cfg);
}

After creating a saver, the state can be saved using a KConfigGroup.

It is also possible to save and restore state directly by using the restoreSelection, restoreExpanded etc methods. Note that the implementation of these methods should return strings that the indexFromConfigString implementation can handle.

class DynamicTreeStateSaver : public KViewStateSerializer
{
    Q_OBJECT
public:
  // ...

    void selectItems(const QList<qint64> &items)
    {
        QStringList itemStrings;
        for (qint64 item : items) {
            itemStrings << QString::number(item);
        }
        restoreSelection(itemStrings);
    }

    void expandItems(const QList<qint64> &items)
    {
        QStringList itemStrings;
        for (qint64 item : items) {
            itemStrings << QString::number(item);
        }
        restoreSelection(itemStrings);
    }
};

Note that a single instance of this class should be used with only one widget. That is don't do this:

saver->setView(treeView1);
saver->setSelectionModel(treeView2->selectionModel());
saver->setScrollArea(treeView3);

To save the state of 3 different widgets, use three savers, even if they operate on the same root model.

saver1->setView(treeView1);
saver2->setSelectionModel(treeView2->selectionModel());
saver3->setScrollArea(treeView3);

It is recommended to restore the state on application startup and after the model has been reset, and to save the state on application close and before the model has been reset.