off method
Implementation
void off({String? name, EventCallBack? cb}) {
if(name == null)
events = {};
else if(events.containsKey(name)) {
if(cb == null)
events.remove(name);
else {
int i = 0;
for(var ev in events[name]!) {
if(ev.cb == cb) {
events[name]!.removeAt(i);
break;
}
i++;
}
}
}
}