Flutter Firestore 流错误 "as required by the closure's context."

Question

我收到以下错误，不知道为什么 The return type 'List<DogModel>' isn't a 'DogModel', as required by the closure's context.

这是我获取流的 Firestore 服务文件

Stream<DogModel> getDogs(String uid) {
return dogCollection.where('userId', isEqualTo: uid).snapshots().map(
      (snapshot) => snapshot.docs
          .map((document) => DogModel.fromFire(document))
          .toList(),
    );

}

这是我的模型

part 'dog_model.g.dart';

enum DogGender {
  male,
  female,
}
enum DogWeight {
  kg,
  lbs,
}

enum DogStatus {
  active,
  training,
  injured,
  retired,
}

@JsonSerializable(explicitToJson: true)
class DogModel {
  String? dogImage;
  String dogName;
  DogBreed? breedInfo;
  @JsonKey(fromJson: dateTimeFromTimestamp, toJson: dateTimeAsIs)
  DateTime? dogBirthday;
  double? dogWeight;
  DogWeight? weightType;
  DogGender? dogGender;
  List<String>? dogType;
  DogStatus? dogStatus;
  bool? registered;
  String? dogChipId;
  @JsonKey(fromJson: dateTimeFromTimestamp, toJson: dateTimeAsIs)
  DateTime? createdAt;
  DogStats? dogStats;
  @JsonKey(ignore: true)
  String? id;
  String? userId;

  DogModel({
    required this.dogImage,
    required this.dogName,
    required this.breedInfo,
    required this.dogBirthday,
    required this.dogWeight,
    required this.weightType,
    required this.dogGender,
    required this.dogType,
    required this.dogStatus,
    required this.registered,
    this.dogStats,
    this.dogChipId,
    this.createdAt,
    this.userId,
    this.id,
  });

  factory DogModel.fromFire(QueryDocumentSnapshot snapshot) {
    return DogModel.fromJson(snapshot as Map<String, dynamic>);
  }

  // JsonSerializable constructor
  factory DogModel.fromJson(Map<String, dynamic> json) =>
      _$DogModelFromJson(json);

  // Serialization
  Map<String, dynamic> toJson() => _$DogModelToJson(this);
}

如果我这样做 Stream<Object> 没问题

Answer 1

getDogs 函数体返回 List<DogModel> 但函数定义是 Stream<DogModel>。因此将定义更改为 Stream<List<DogModel>> 如下：

// fix this   ↓
Stream<List<DogModel>> getDogs(String uid) {
return dogCollection.where('userId', isEqualTo: uid).snapshots().map(
      (snapshot) => snapshot.docs
          .map((document) => DogModel.fromFire(document))
          .toList(), // <~~~~ you're returning a list here 
    );

Answer 2

您已将 return 类型的方法 getDogs() 定义为 Stream<DogModel> 而您的方法 return 是 Stream<List<DogModel>>，即 return List 个 DogModel 秒。所以你的 getDogs() 方法声明应该是这样的：

Stream<<List<DogModel>> getDogs(String uid) {
  ...
}

Flutter Firestore 流错误 "as required by the closure's context."

Flutter Firestore Stream error "as required by the closure's context."

firebase

flutter

google-cloud-firestore

provider