on method
持久化监听
Implementation
void on(String name, EventListener listener, {int? limit}) {
// 默认 limit 0 = 没有次数限制
final container = _EventContainer(listener, limit ?? -1);
if (_containers.containsKey(name)) {
_containers[name]!.add(container);
} else {
_containers[name] = [container];
}
}