Flutter State-01

参考

王叔 FLutter 状态管理篇

语雀的个人草稿笔记

自定义 Provider

class CustomProvider<T extends Listenable> extends StatefulWidget {
  final T Function() create;
  final Widget child;
  const CustomProvider({Key? key, required this.child, required this.create}) : super(key: key);

  @override
  State<CustomProvider> createState() => _CustomState<T>();

  static T of<T>(BuildContext context,{bool listen = true}) {
    if(listen) {
      return context.dependOnInheritedWidgetOfExactType<CustomInheritedWidget<T>>()!.model;
    } else {
      return (context.getElementForInheritedWidgetOfExactType<CustomInheritedWidget<T>>()!.widget as CustomInheritedWidget).model;
    }

  }
}

class _CustomState<T extends Listenable> extends State<CustomProvider<T>> {

  late T model;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    model = widget.create();
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: model,
      builder: (BuildContext context, Widget? child) {
        return CustomInheritedWidget(model: model,
            child: widget.child);
      },
    );
  }
}


class CustomInheritedWidget<T> extends InheritedWidget {
  final T model;

  const CustomInheritedWidget({super.key, required this.model,required super.child});

  static CustomInheritedWidget of<T>(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<CustomInheritedWidget<T>>()!;
  }

  @override
  bool updateShouldNotify(covariant InheritedWidget oldWidget) {
    print("update");
    return true;
  }
}

/// extension如果没有取名字只能在本文件中使用，属于私有扩展。起名字可以供其他外部使用
extension Consumer on BuildContext {
  T watch<T>() => CustomProvider.of(this);
  T read<T>() => CustomProvider.of(this,listen: false);
}