toggleSelection method
Implementation
void toggleSelection(int index) {
final newSelected = Set<int>.from(selected.value);
if (widget.singleSelect) {
if (newSelected.contains(index)) {
newSelected.clear();
} else {
newSelected
..clear()
..add(index);
}
} else {
if (newSelected.contains(index)) {
newSelected.remove(index);
} else {
newSelected.add(index);
}
}
selected.value = newSelected;
}