focusInto method
void
focusInto()
→ key: expand a collapsed folder, else step into the first child.
Implementation
void focusInto() {
final id = focused;
if (id == null) return;
final n = node(id);
if (n == null) return;
if (n.isFolder && n.hasChildren && !_expanded.contains(id)) {
_expanded.add(id);
notifyListeners();
} else if (n.hasChildren) {
_focused = n.children.first.id;
notifyListeners();
}
}