updateSections method
adds or removes a section key from the list of open sections and notifies sections to open or close accordingly
Implementation
void updateSections(UniqueKey key) {
openSections.contains(key)
? openSections.remove(key)
: openSections.add(key);
while (openSections.length > maxOpenSections) {
openSections.removeAt(0);
}
controllerIsOpen.sink.add('update list');
}