updateElement method
Implementation
@override
updateElement(Group element, {int? index}) {
int matchedIndex;
if (index == null) {
matchedIndex = getMatchingIndex(element);
} else {
matchedIndex = index;
}
if (index != -1) {
element.hasJoined = list[matchedIndex].hasJoined;
}
super.updateElement(element, index: matchedIndex);
}