HowTo restore QTreeView last expanded state?

These two function by using a loop should do that for you:

QModelIndexList QAbstractItemModel::persistentIndexList () const
bool isExpanded ( const QModelIndex & index ) const

First, thanks to Razi for persistentIndexList and isExpanded way.

Second, here is the code which works for me just fine :-)

dialog.h file:

class Dialog : public QDialog
{
    Q_OBJECT;

    TreeModel *model;
    TreeView *view;

public:
    Dialog(QWidget *parent = 0);
    ~Dialog(void);

    void reload(void);

protected:
    void createGUI(void);
    void closeEvent(QCloseEvent *);
    void saveState(void);
    void restoreState(void);
};

dialog.cpp file:

Dialog::Dialog(QWidget *parent)
{
    createGUI();
    reload();
}

Dialog::~Dialog(void) {};

void Dialog::reload(void)
{
    restoreState();
}

void Dialog::createGUI(void)
{
    QFile file(":/Resources/default.txt");
    file.open(QIODevice::ReadOnly);
    model = new TreeModel(file.readAll());
    file.close();

    view = new TreeView(this);
    view->setModel(model);

    QVBoxLayout *mainVLayout = new QVBoxLayout;
    mainVLayout->addWidget(view);

    setLayout(mainVLayout);
}

void Dialog::closeEvent(QCloseEvent *event_)
{
    saveState();
}

void Dialog::saveState(void)
{
    QStringList List;

    // prepare list
    // PS: getPersistentIndexList() function is a simple `return this->persistentIndexList()` from TreeModel model class
    foreach (QModelIndex index, model->getPersistentIndexList())
    {
        if (view->isExpanded(index))
        {
            List << index.data(Qt::DisplayRole).toString();
        }
    }

    // save list
    QSettings settings("settings.ini", QSettings::IniFormat);
    settings.beginGroup("MainWindow");
    settings.setValue("ExpandedItems", QVariant::fromValue(List));
    settings.endGroup();
}

void Dialog::restoreState(void)
{
    QStringList List;

    // get list
    QSettings settings("settings.ini", QSettings::IniFormat);
    settings.beginGroup("MainWindow");
    List = settings.value("ExpandedItems").toStringList();
    settings.endGroup();

    foreach (QString item, List)
    {
        // search `item` text in model
        QModelIndexList Items = model->match(model->index(0, 0), Qt::DisplayRole, QVariant::fromValue(item));
        if (!Items.isEmpty())
        {
            // Information: with this code, expands ONLY first level in QTreeView
            view->setExpanded(Items.first(), true);
        }
    }
}

Have a nice day!)

---

PS: this example based on C:\Qt\4.6.3\examples\itemviews\simpletreemodel code.

Here is a general approach that should work with any QTreeView based widget, that uses some sort of ID system to identify elements (I am assuming the ID is an int, which is stored inside the Qt::UserRole):

void MyWidget::saveExpandedState()
{
    for(int row = 0; row < tree_view_->model()->rowCount(); ++row)
        saveExpandedOnLevel(tree_view_->model()->index(row,0));
}

void Widget::restoreExpandedState()
{
    tree_view_->setUpdatesEnabled(false);

    for(int row = 0; row < tree_view_->model()->rowCount(); ++row)
        restoreExpandedOnLevel(tree_view_->model()->index(row,0));

    tree_view_->setUpdatesEnabled(true);
}

void MyWidget::saveExpandedOnLevel(const QModelIndex& index)
{
    if(tree_view_->isExpanded(index)) {
        if(index.isValid())
            expanded_ids_.insert(index.data(Qt::UserRole).toInt());
        for(int row = 0; row < tree_view_->model()->rowCount(index); ++row)
            saveExpandedOnLevel(index.child(row,0));
    }
}

void MyWidget::restoreExpandedOnLevel(const QModelIndex& index)
{
    if(expanded_ids_.contains(index.data(Qt::UserRole).toInt())) {
        tree_view_->setExpanded(index, true);
        for(int row = 0; row < tree_view_->model()->rowCount(index); ++row)
            restoreExpandedOnLevel(index.child(row,0));
    }
}

Instead of MyWidget::saveExpandedState() and MyWidget::saveExpandedState() one could also directly call MyWidget::saveExpandedOnLevel(tree_view_->rootIndex()) and MyWidget::restoreExpandedOnLevel(tree_view_->rootIndex()). I only used the above implementation because the for loop will be called anyway and MyWidget::saveExpandedState() and MyWidget::saveExpandedState() looked cleaner with my SIGNAL and SLOT design.

Thanks to Razi and mosg I was able to get this working. I made it restore the expanded state recursively so I thought I would share that part.

void applyExpandState_sub(QStringList& expandedItems,
                          QTreeView* treeView,
                          QAbstractItemModel* model,
                          QModelIndex startIndex)
{
    foreach (QString item, expandedItems) 
    {
        QModelIndexList matches = model->match( startIndex, Qt::UserRole, item );
        foreach (QModelIndex index, matches) 
        {
            treeView->setExpanded( index, true );
            applyExpandState_sub(expandedItems, 
                                 treeView,
                                 model,
                                 model->index( 0, 0, index ) );
        }
    }
}

Then use like:

void myclass::applyExpandState() 
{
    m_treeView->setUpdatesEnabled(false);

    applyExpandState_sub( m_expandedItems,
                          m_treeView,
                          m_model,
                          m_model->index( 0, 0, QModelIndex() ) );

    m_treeView->setUpdatesEnabled(true);
}

I am using the Qt::UserRole here because multiple items in my model can have the same display name which would mess up the expand state restoration, so the UserRole provides a unique identifier for each item to avoid that problem.