flutter：类型'(DocumentSnapshot<MyObject>) => MyObject' 不是类型'(DocumentSnapshot<Object>) => MyObject' 的子类型

Question

我很难从 firebase DB 读取（和显示）数据。我收到此警告：类型“(DocumentSnapshot) => GivitUser”不是类型“(DocumentSnapshot) => GivitUser”的子类型

我真的不知道我做错了什么，我尝试从 DocumentSnapshot 转换为 DocumentSnapshot 但没有成功。这是我的 database.dart 文件：

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'package:givit_app/models/givit_user.dart';

class DatabaseService {
  final String uid;
  DatabaseService({@required this.uid});

  final CollectionReference userCollection =
      FirebaseFirestore.instance.collection('Users');

  Future<void> updateGivitUserData(
      String email, String fullName, String password, int phoneNumber) async {
    return await userCollection.doc(uid).set({
      'Email': email,
      'Full Name': fullName,
      'Password': password,
      'Phone Number': phoneNumber,
    });
  }

  Future<GivitUser> getGivitUser(String uid) async {
    return await userCollection.doc(uid).get().then((user) => user.data());
  }

  GivitUser _userDataFromSnapshot(DocumentSnapshot<GivitUser> snapshot) {
    return GivitUser(
      uid: uid,
      email: snapshot.data().email,
      fullName: snapshot.data().fullName,
      phoneNumber: snapshot.data().phoneNumber,
    );
  }

  Stream<GivitUser> get userData {
    return userCollection.doc(uid).snapshots().map(_userDataFromSnapshot);
  }
}

这是我尝试使用 database.dart 文件并显示数据的地方：

  Widget build(BuildContext context) {
    GivitUser user = Provider.of<GivitUser>(context);
    final DatabaseService db = DatabaseService(uid: user.uid);
    return StreamBuilder<GivitUser>(
        stream: db.userData,
        builder: (context, snapshot) {
          if (!snapshot.hasData) {
            return Loading();
          }
          print('after getter');
          print(snapshot.data);
          GivitUser givitUser = snapshot.data;
          return Scaffold(
          ....
          ....
          ....

提前致谢，如有任何帮助，我将不胜感激:)

编辑：错误截图： ERROR SCREENSHOT

Answer 1

这一行 userCollection.doc(uid).snapshots() returns Stream<DocumentSnapshot> 而不是你在 _userDataFromSnapshot 参数中声明的 Stream<DocumentSnapshot<GivitUser>>。

Reference

Stream<DocumentSnapshot> snapshots({bool includeMetadataChanges = false})

您需要更改以下代码块：

    GivitUser _userDataFromSnapshot(DocumentSnapshot<GivitUser> snapshot) {
        //...
      }

对此：

    GivitUser _userDataFromSnapshot(DocumentSnapshot snapshot) {
       //...
      }

snapshot.data() returns 一个 Map<String, dynamic> 对象。因此，您可以像从地图对象中获取数据一样获取数据。

_userDataFromSnapshot方法可以更新为：

    GivitUser _userDataFromSnapshot(DocumentSnapshot snapshot) {
        var snapshotData = snapshot.data() as Map;
        return GivitUser(
           uid: uid,
           email: snapshotData['Email'],
           fullName: snapshotData['Full Name'],
           phoneNumber: snapshotData['Phone Number'],
        );
   }

Answer 2

我确实遇到了这个问题，帮助我的是首先尝试获取集合然后处理这个特定文档，也许尝试更改此代码：

final DatabaseService db = DatabaseService(uid: user.uid);
return StreamBuilder<GivitUser>(
    stream: db.userData,

此代码：

final DatabaseService db = DatabaseService(uid: user.uid);
return StreamBuilder<GivitUser>(
    stream: db.userCollection.doc(db.uid).get(),

就像这个文件说的那样https://firebase.flutter.dev/docs/firestore/usage/#one-time-read

然后您可以像这样进入该字段：

builder: (context, snapshot) {
/...
    Map<String, dynamic> data = snapshot.data.data();

希望对你也有帮助！ :)

flutter：类型'(DocumentSnapshot<MyObject>) => MyObject' 不是类型'(DocumentSnapshot<Object>) => MyObject' 的子类型

flutter: type '(DocumentSnapshot<MyObject>) => MyObject' is not a subtype of type '(DocumentSnapshot<Object>) => MyObject'

firebase

flutter

google-cloud-firestore

stream-builder