stream<T> static method
转为 Stream
Implementation
static Stream<T> stream<T>(dynamic target) {
final controller = StreamController<T>.broadcast();
final notifier = obtain<T>(target);
// 推送当前值
if (notifier.value != null) controller.add(notifier.value);
void listener(dynamic value) => controller.add(value as T);
addListener(target, listener);
controller.onCancel = () => _listeners[target]?.remove(listener);
return controller.stream;
}