this, SLOT(on_item_changed(const QModelIndex&)));
connect(tree_view_, SIGNAL(activated(const QModelIndex&)),
this, SLOT(on_item_activated(const QModelIndex&)));
this, SLOT(on_item_changed(const QModelIndex&)));
connect(tree_view_, SIGNAL(activated(const QModelIndex&)),
this, SLOT(on_item_activated(const QModelIndex&)));