为咖啡馆应用程序添加评分功能的

为了允许用户对餐馆进行评分，需要使用Flutter中的Cloud Firestore - 一个云存储解决方案。在Firestore中创建一个'cafe'集合，并在该集合中创建一个'documents'文件夹，用于存储和检索餐馆的详细信息和评分。

首先，需要在应用程序中创建一个'cafe'类，其中包含餐馆的名称、位置、描述等信息，以及最新的评分数组：

class Cafe {
  String name;
  String location;
  String description;
  List ratings;

  Cafe({this.name, this.location, this.description, this.ratings});

  factory Cafe.fromFirestore(DocumentSnapshot snapshot) {
    return Cafe(
      name: snapshot.data["name"],
      location: snapshot.data["location"],
      description: snapshot.data["description"],
      ratings: List.from(snapshot.data["ratings"]),
    );
  }

  Map toFirestore() {
    return {
      "name": name,
      "location": location,
      "description": description,
      "ratings": ratings,
    };
  }
}

接下来，创建一个'RateCafe' widget，用于显示可以评分的餐馆列表。在此widget中，使用Firestore进行数据获取、添加和更新操作。

class RateCafe extends StatefulWidget {
  @override
  _RateCafeState createState() => _RateCafeState();
}

class _RateCafeState extends State {
  final GlobalKey _formKey = GlobalKey();
  final TextEditingController _ratingController = TextEditingController();

  List cafes = [];

  final _firestore = Firestore.instance;

  @override
  void initState() {
    super.initState();
    // 获取餐馆列表
    _getListOfCafes();
  }

  void _getListOfCafes() async {
    QuerySnapshot snapshot =
        await _firestore.collection("cafes").getDocuments();
    setState(() {
      cafes = snapshot.documents
          .map((doc) => Cafe.fromFirestore(doc))
          .toList();
    });
  }

  void _addRating(int index) async {
    Cafe cafe = cafes[index];
    double rating = double.parse(_ratingController.text);
    cafe.ratings.add(rating);
    await _firestore
        .collection("cafes")
        .document(index.toString())
        .setData(cafe.toFirestore());
    setState(() {});
    _ratingController.clear();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("评分餐馆"),
      ),
      body: SingleChildScrollView(
        child: Column(
          children: cafes
              .asMap()
              .entries
              .map(
                (entry) => ListTile(
                  title: Text(entry.value.name),
                  subtitle: Text(entry.value.description),
                  trailing: Form(
                    key: _formKey,
                    child: Column(
                      children: [
                        TextFormField(
                          controller: _ratingController,
                          keyboardType: TextInputType.numberWithOptions(
                              decimal: true, signed: false),
                          decoration: InputDecoration(
                            labelText: "您的评分",
                          ),
                          validator: (value) {
                            if (value.isEmpty) {
                              return "评分不能为空";
                            }
                            if (double.parse(value) < 0