rememberValueNotifier<T> method

ValueNotifier<T> rememberValueNotifier<T>({ T? value, T factory()?, T factory2(Lifecycle)?, FutureOr<void> onDispose(ValueNotifier<T>)?, bool listen = false, Object? key, })

快速生成一个可用的类型 ValueNotifier

• 确定是否需要更新对象只有 type 和 key
• value， factory， factory2 确定如何初始化的创建一个 ValueNotifier 必须有一个不能为空 不作为更新key
• listen 当前的 Context 自动监听生成的 ValueNotifier 不作为更新key 只有首次有效 后续变化无效

Implementation

ValueNotifier<T> rememberValueNotifier<T>({
  T? value,
  T Function()? factory,
  T Function(Lifecycle)? factory2,
  FutureOr<void> Function(ValueNotifier<T>)? onDispose,
  bool listen = false,
  Object? key,
}) =>
    remember<ValueNotifier<T>>(
      factory2: (l) {
        assert(value != null || factory != null || factory2 != null,
            'value and factory and factory2 cannot be null at the same time');
        value ??= factory?.call();
        value ??= factory2?.call(l);
        final r =
            CancellableValueNotifier(value as T, l.makeLiveCancellable());
        if (listen && this is Element) {
          final rContext = WeakReference(this);
          r.addCListener(l.makeLiveCancellable(), () {
            final element = rContext.target as Element?;
            if (element != null) {
              element.markNeedsBuild();
            }
          });
        }
        return r;
      },
      onDispose: (d) {
        d.dispose();
        onDispose?.call(d);
      },
      key: FlexibleKey(value, factory, factory2, key),
    );