type '_Map<String, dynamic>' 不是类型 cast 中类型 'User' 的子类型

Question

我一直在尝试使用用户数据模型从 Firestore 读取数据。如果我使用 CollectionReference 类型的变量读取引用集合，并使用自定义构建函数读取 FutureBuilder 中的文档列表，并将其映射到 Map 中，直接在我读取数据的同一个文件中，它工作正常。但是当我尝试使用我创建的用户模型作为用户检索快照数据时，它显示了这个错误。

我试图在用户模型中更改地图的定义但它不起作用，我做错了什么？

我的主页（我称之为读取数据的地方）

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_project_1/screens/home/read_data.dart';
import 'package:firebase_project_1/screens/home/update_profile.dart';
import 'package:flutter/material.dart';
import 'package:get/get.dart';

class Home extends StatefulWidget {
  const Home({super.key});

  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> {
  final user = FirebaseAuth.instance.currentUser!;

  // The list of all document IDs,
  //which have access to each their own personal information
  List<String> documentIDs = [];

  // DocumentReference<Map<String, dynamic>>(Users/8bu245T440NIuQnJhm81)
  // This is the sample output, to get IDs we just do .id

  Future getDocIDs() async {
    await FirebaseFirestore.instance
        .collection('Users')
        .orderBy('rank', descending: false)
        .get()
        .then((snapshot) => {
              snapshot.docs.forEach((document) {
                print(document.reference);
                documentIDs.add(document.reference.id);
              })
            });

    setState(() {});
  }

  @override
  void initState() {
    getDocIDs();
    super.initState();
    documentIDs = [];
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.deepPurple,
        title: Center(
          child: Text(
            textAlign: TextAlign.center,
            'Display dashboard',
            style: TextStyle(
              fontSize: 30,
              color: Colors.tealAccent.shade400,
            ),
          ),
        ),
        actions: [
          GestureDetector(
            onTap: () {
              FirebaseAuth.instance.signOut();
            },
            child: const Padding(
              padding: EdgeInsets.symmetric(horizontal: 10.0),
              child: Icon(
                Icons.logout_sharp,
              ),
            ),
          )
        ],
      ),
      backgroundColor: Colors.deepPurple.shade200,
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            // This has a FutureBuilder as it needs
            // to wait for executiion of getDocIDs function to finish execution
            Expanded(
              child: Padding(
                padding: const EdgeInsets.all(10.0),
                child: ListView.builder(
                  itemCount: documentIDs.length,
                  itemBuilder: (context, index) {
                    return Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: ListTile(
                        shape: BeveledRectangleBorder(
                          borderRadius: BorderRadius.circular(20),
                          side: const BorderSide(
                            width: 2,
                            color: Colors.indigo,
                          ),
                        ),
                        title: ReadData(docIDs: documentIDs[index]),
                        tileColor: Colors.indigo.shade300,
                      ),
                    );
                  },
                ),
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => Get.to(() => UpdateProfile()) ,
        backgroundColor: Colors.tealAccent,
        child: const Icon(Icons.edit),
      ),
    );
  }
}

读取用户数据的我的文件

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_project_1/user_model/user_model.dart';
import 'package:flutter/material.dart';

class ReadData extends StatelessWidget {
  const ReadData({required this.docIDs, super.key});

  final String docIDs;

  @override
  Widget build(BuildContext context) {
    // get the collection
    CollectionReference users = FirebaseFirestore.instance.collection('Users');

    return FutureBuilder<DocumentSnapshot>(
      future: users.doc(docIDs).get(),
      builder: (context, snapshot) {
        //IF connection with the firebase is ensured, then we execute
        if (snapshot.connectionState == ConnectionState.done) {
          //We are trying to map the key and values pairs
          //to a variable called "data" of Type Map
          //Map<String, dynamic> data =
              //snapshot.data!.data() as Map<String, dynamic>;

          if (snapshot.hasData) {
          User data = snapshot.data!.data() as User;

          return Text(
            //'${data['rationType']},' +
              '${data.rationType}, ' +
              ' ' +
              'Rank:' +
              ' ' +
              //'${data['rank']}');

                '${data.rank}');
                }
        }
        return const Text('Loading......');
        //Map<String, dynamic> data = User.fromJson(snapshot.data!.data())

        //Returning the value for key called name
      },
    );
  }
}

用户模型

import 'package:json_annotation/json_annotation.dart';
import 'package:cloud_firestore_odm/cloud_firestore_odm.dart';

@JsonSerializable(explicitToJson: true)
class User {
  User({
    required this.rank,
    required this.appointment,
    required this.rationType,
    required this.status,
    required this.mobileNumber,
    required this.bloodgroup,
    required this.dob,
    required this.ord,
    required this.attendence,
  });

  factory User.fromJson(Map<String, dynamic> json) {
    return User(
      rank: json['rank'],
      appointment: json['appointment'],
      rationType: json['rationType'],
      status: json['status'],
      mobileNumber: json['mobileNumber'],
      bloodgroup: json['bloodgroup'],
      dob: json['dob'],
      ord: json['ord'],
      attendence: json['attendence'],
    );
  }

  final String rank;
  final String appointment;
  final String rationType;
  final String status;
  final String mobileNumber;
  final String bloodgroup;
  final String dob;
  final String ord;
  final String attendence;

  Map<String, Object?> toJson() {
    return {
      'rank'        :  rank,
      'appointment' :  appointment,
      'rationType'  :  rationType,  
      'status'      :  status,  
      'mobileNumber':  mobileNumber,          
      'bloodgroup'  :  bloodgroup,        
      'dob'         :  dob,      
      'ord'         :  ord,  
      'attendence'  :  attendence,
    };
  }
}

Answer 1

尝试如下类型铸造：

 User data =
          User.fromJson(snapshot.data() as Map<String, dynamic>);