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Я создаю систему, в которой только определенный пользователь может видеть список проектов. Список проектов будет показан в пользовательском приложении, когда проекты будут назначены им через администрацию с помощью электронной почты пользователя. Я использую flutter и Google firebase

Я пытался использовать оператор If else, но, похоже, не могу этого сделать. У меня есть 2 класса моделей

Класс User_model

 import 'package:firebase_auth/firebase_auth.dart';

class Users{
  final String uid;
  Users({this.uid});
}

class UserModel{
  String uid;
  String email;
  String name;
  String employeeID;
  String phonenumber;
  String position;

  UserModel({this.uid, this.email, this.name, this.employeeID, this.phonenumber, this.position});

  //receiving data from server
  factory UserModel.fromMap(map){
    return UserModel(
      uid: map['uid'],
      email: map['email'],
      name: map['name'],
      employeeID: map['employeeID'],
      phonenumber: map['phonenumber'],
      position: map['position'],
    );
  }

  //sending data to our server
  Map<String, dynamic> toMap(){
    return{
      'uid': uid,
      'email': email,
      'name' : name,
      'employeeID' : employeeID,
      'phonenumber' : phonenumber,
      'position' : position,
    };
  }
}

class UserProject{
  final String projectid;
  final String address;
  final String titleproject;
  final List<String> assignedmember ;

  UserProject({this.projectid, this.address, this.titleproject, this.assignedmember});
}
 

Класс Project_model

 import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';

class Project{
  final String address;
  final String titleproject;
  final List<dynamic> assignedmember;

  Project({this.address, this.titleproject, this.assignedmember});

}
 

Рабочий стол.дротик

 import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:smartconstructionreport/data/project_model.dart';
import 'package:smartconstructionreport/data/user_model.dart';
import 'package:smartconstructionreport/screens/project_screen.dart';
import 'package:smartconstructionreport/theme.dart';
import 'package:smartconstructionreport/widget/ProjectCard.dart';
import 'package:smartconstructionreport/widget/menulist.dart';
import 'package:smartconstructionreport/service/database.dart';
import 'package:provider/provider.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:smartconstructionreport/widget/projectlist.dart';

import 'FloorPlan.dart';

class HomeScreen extends StatefulWidget {
  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  User user = FirebaseAuth.instance.currentUser;
  UserModel loggedInUser = UserModel();

  @override
  void initState(){
    super.initState();
    FirebaseFirestore.instance
    .collection("user")
    .doc(user.uid)
    .get()
    .then((value){
      this.loggedInUser = UserModel.fromMap(value.data());
      setState(() {});
    });
  }

  Widget build(BuildContext context) {
    return StreamProvider<List<Project>>.value(
      value: DatabaseService().projects,
      child: Scaffold(
        drawer: menulist(),
        appBar: AppBar(
          backgroundColor: kPrimaryColor,
          centerTitle: true,
          title: Image.asset('images/scdr logo.png',
          fit: BoxFit.cover,),
        ),
        body: SingleChildScrollView(
          child: Padding(
            padding: kDefaultPadding,
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                SizedBox(
                  height: 30,
                ),
                Text(
                  "Hello ${loggedInUser.name},",
                  style: TextStyle(color: Colors.black,
                      fontSize: 25,
                      fontWeight: FontWeight.w700),
                ),
                SizedBox(
                  height: 5,
                ),
                Text(
                  'Have a great day ahead!',
                  style: TextStyle(color: Colors.black,
                    fontSize: 12,
                  ),
                ),
                SizedBox(
                  height: 5,
                ),
                Text(
                  'Lets start working!',
                  style: TextStyle(color: Colors.black,
                    fontSize: 12,
                  ),
                ),
                SizedBox(
                  height: 30,
                ),
                Text(
                  'Project Lists',
                  style: TextStyle(color: Colors.black,
                      fontSize: 25,
                      fontWeight: FontWeight.w700),
                ),
                SizedBox(
                  height: 18,
                ),
                ProjectList(),
              ],
            ),
          ),
        ),
      ),
    );
  }

}
 

ProjectList.dart
I tried to add If else statement to check if the project contains email assigned to the project. But it return null

 import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:provider/provider.dart';
import 'package:smartconstructionreport/data/project_model.dart';
import 'package:smartconstructionreport/screens/project_screen.dart';

import 'ProjectCard.dart';

class ProjectList extends StatefulWidget {
  @override
  _ProjectListState createState() => _ProjectListState();
}

class _ProjectListState extends State<ProjectList> {
  User user = FirebaseAuth.instance.currentUser;
  Project projectmember = Project();

  @override
  Widget build(BuildContext context) {
    final projects = Provider.of<List<Project>>(context)  ?? [];

    return ListView.builder(
        shrinkWrap: true,
        itemCount: projects.length,
        itemBuilder: (context, index) {
        if (projectmember.assignedmember.contains(user.email)) {
          return ProjectCard(project: projects[index],
            press: () {
              Navigator.push(context, MaterialPageRoute(
                builder: (context) => ProjectScreen(),
              ));
            },
          );
        };
        }
    );
  }
}
 

Проектная карта.дротик

 import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:smartconstructionreport/data/project_model.dart';
import 'package:smartconstructionreport/theme.dart';

class ProjectCard extends StatelessWidget {

  final Function press;
  final Project project;
  ProjectCard({this.project, this.press});

  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    return GestureDetector(
      onTap: press,
      child: Card(
        clipBehavior: Clip.antiAlias,
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(20.0)
        ),
        elevation: 10,
        margin: EdgeInsets.fromLTRB(5.0, 15.0, 5.0, 10.0),
        child: Column(
          children: [
            Stack(
              alignment: Alignment.center,
              children: [
                Padding(
                  padding: const EdgeInsets.all(2.0),
                  child: Text(
                    project.titleproject,
                    style: TextStyle(
                      fontSize: 17,
                      fontWeight: FontWeight.bold,
                    ),
                  ),
                )
              ],
            ),
            Divider(color: Colors.black),
            Padding(
              padding: EdgeInsets.fromLTRB(10.0, 5.0, 5.0, 0.0),
              child: Text(
                project.address,
                style: TextStyle(fontSize: 14),),
            ),
            Row(
              children: [
                Column(
                  children: [
                    TextButton.icon(
                        onPressed: (){},
                        icon: Icon(Icons.person,
                          color: kPrimaryColor,) ,
                        label: Text('Project Manager')),
                  ],
                ),
                SizedBox(width:50),
                Column(
                  children: [
                    TextButton.icon(
                        onPressed: (){},
                        icon: Icon(Icons.location_pin,
                          color: kPrimaryColor,) ,
                        label: Text('MAP')),
                  ],
                )
              ],
            ),
          ],
        ),
      ),
    );
  }
}
 

Ошибка

 ======== Exception caught by widgets library =======================================================
The method 'contains' was called on null.
Receiver: null
Tried calling: contains("rashid@fyp.com")
====================================================================================================