颤振“imageUrl 被调用为空”

Question

我遇到了“图像 url 被调用为 null”的问题。我已经定义了ImageUrl，但我不知道问题出在哪里。

我在add_contact.dart中添加了future builder，但是问题没有解决。我不知道我应该在哪里使用 future builder。

here is the image

这是我的代码：

home_page.dart

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:pop/widgets/add_contact.dart';
import 'package:pop/widgets/user_item.dart';
import '../providers/user.dart';

import 'package:provider/provider.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    final products = Provider.of<Users>(context).items;
    return Scaffold(
      appBar: AppBar(
        title: Text('Pop'),
        actions: [
          PopupMenuButton(
            child: Icon(Icons.more_vert, color: Colors.white),
            itemBuilder: (context) => [
              PopupMenuItem(
                child: Text('add account to chat'),
                value: 'add',
              ),
              PopupMenuItem(
                child: Text('logout'),
                value: 'logout',
              ),
            ],
            onSelected: (val) {
              switch (val) {
                case 'logout':
                  FirebaseAuth.instance.signOut();
                  break;
                case 'add':
                  showModalBottomSheet(
                    context: context,
                    builder: (ctx) => AddContact(),
                  );
                  break;
                default:
              }
            },
          ),
        ],
      ),
      body: ListView.builder(
        itemCount: products.length,
        itemBuilder: (ctx, i) => ChangeNotifierProvider.value(
          value: products[i],
          child: UserButton(
            products[i].imageUrl,
            products[i].name,
            products[i].phoneNumber,
          ),
        ),
      ),
    );
  }
}

user.dart

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

class UserItem with ChangeNotifier {
  final String name;
  final String phoneNumber;
  final String imageUrl;
  UserItem({
    @required this.name,
    @required this.phoneNumber,
    @required this.imageUrl,
  });
}

class Users with ChangeNotifier {
  List<UserItem> _items = [];

  List<UserItem> get items {
    return [..._items];
  }

  Future<void> addItem(String phone) async {
    UserItem newItem;
    await FirebaseFirestore.instance
        .collection('users')
        .where('phone_number', isEqualTo: phone)
        .get()
        .then(
          (QuerySnapshot value) => value.docs.forEach(
            (element) {
              newItem = UserItem(
                name: element['username'],
                phoneNumber: element['phone_number'],
                imageUrl: element['image_url'],
              );
            },
          ),
        );
    _items.add(newItem);
    notifyListeners();
  }
}

add_contact.dart

import 'dart:async';

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:intl_phone_number_input/intl_phone_number_input.dart';
import 'package:provider/provider.dart';
import '../providers/user.dart';

class AddContact extends StatefulWidget {
  @override
  _AddContactState createState() => _AddContactState();
}

class _AddContactState extends State<AddContact> {
  PhoneNumber number;
  bool isLoading = false;
  final Stream<DocumentSnapshot> _query = FirebaseFirestore.instance
      .collection('users')
      .doc(FirebaseAuth.instance.currentUser.uid)
      .snapshots();
  @override
  Widget build(BuildContext context) {
    return Form(
      child: Container(
        padding: EdgeInsets.only(
            bottom: MediaQuery.of(context).viewInsets.bottom + 10),
        child: SingleChildScrollView(
          child: Column(
            // mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              StreamBuilder<DocumentSnapshot>(
                stream: _query,
                builder: (context, snapshot) {
                  if (snapshot.connectionState == ConnectionState.waiting) {
                    return CircularProgressIndicator();
                  }
                  return InternationalPhoneNumberInput(
                    initialValue: PhoneNumber(
                      isoCode: snapshot.data['iso_code'],
                    ),
                    onInputChanged: (val) {
                      number = val;
                    },
                  );
                },
              ),
              isLoading
                  ? CircularProgressIndicator()
                  : RaisedButton.icon(
                      color: Colors.amber,
                      onPressed: () {
                        FutureBuilder(
                          future: Provider.of<Users>(context, listen: false)
                              .addItem(number.phoneNumber),
                          builder: (ctx, snapshot) {
                            if (snapshot.connectionState ==
                                ConnectionState.waiting) {
                              isLoading = true;
                            }
                            isLoading = false;
                          },
                        );
                        Navigator.of(context).pop();
                      },
                      label: Text('add contact'),
                      icon: Icon(Icons.add),
                    ),
            ],
          ),
        ),
      ),
    );
  }
}