Firebase Query 不适用于 Flutter，如何解决？

Question

我正在尝试向我的 Flutter 应用程序添加搜索功能，代码中一切正常，没有显示错误，但是当我在应用程序屏幕上搜索用户名时没有显示结果，但有时它会引发错误，提示“失败断言：第 269 行 pos 10: 'data != null' 相关的导致错误的小部件是 FutureBuilder" 尤其是当我使用大写字母并且文本中有空格时。

我附上了 search.dart 和 user.dart 文件的代码。请帮帮我，我被困在这里了。

search.dart 文件

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'package:flutter_svg/flutter_svg.dart';
import 'package:social_share/models/user.dart';
import 'package:social_share/pages/home.dart';
import 'package:social_share/widgets/progress.dart';

class Search extends StatefulWidget {
  @override
  _SearchState createState() => _SearchState();
}

class _SearchState extends State<Search> {
  TextEditingController searchController = TextEditingController();
  Future<QuerySnapshot> searchResultsFuture;

  handleSearch(String query) {
    Future<QuerySnapshot> users = usersRef
        .where("displayName", isGreaterThanOrEqualTo: query)
        .getDocuments();
    setState(() {
      searchResultsFuture = users;
    });
  }

  clearSearch() {
    searchController.clear();
  }

  AppBar buildSearchField() {
    return AppBar(
      backgroundColor: Colors.white,
      title: TextFormField(
        controller: searchController,
        decoration: InputDecoration(
          hintText: "Search for a user...",
          filled: true,
          prefixIcon: Icon(
            Icons.account_box,
            size: 28.0,
          ),
          suffixIcon: IconButton(
            icon: Icon(Icons.clear),
            onPressed: clearSearch,
          ),
        ),
        onFieldSubmitted: handleSearch,
      ),
    );
  }

  Container buildNoContent() {
    final Orientation orientation = MediaQuery.of(context).orientation;
    return Container(
      child: Center(
        child: ListView(
          shrinkWrap: true,
          children: <Widget>[
            SvgPicture.asset(
              'assets/images/search.svg',
              height: orientation == Orientation.portrait ? 300.0 : 200.0,
            ),
            Text(
              "Find Users",
              textAlign: TextAlign.center,
              style: TextStyle(
                color: Colors.white,
                fontStyle: FontStyle.italic,
                fontWeight: FontWeight.w600,
                fontSize: 60.0,
              ),
            ),
          ],
        ),
      ),
    );
  }

  buildSearchResults() {
    return FutureBuilder(
      future: searchResultsFuture,
      builder: (context, snapshot) {
        if (!snapshot.hasData) {
          return circularProgress();
        }
        List<Text> searchResults = [];
        snapshot.data.documents.forEach((doc) {
          User user = User.fromDocument(doc);
          searchResults.add(Text(user.username , style: TextStyle(color: Colors.black, fontSize: 20.0),));
        });
        return ListView(
          children: searchResults,
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Theme.of(context).primaryColor.withOpacity(0.8),
      appBar: buildSearchField(),
      body:
          searchResultsFuture == null ? buildNoContent() : buildSearchResults(),
    );
  }
}

class UserResult extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text("User Result");
  }
}

user.dart 文件

import 'package:cloud_firestore/cloud_firestore.dart';

class User {
  final String id;
  final String username;
  final String email;
  final String photoUrl;
  final String displayName;
  final String bio;


  //Constructor
  User({
    this.id,
    this.username,
    this.email,
    this.photoUrl,
    this.displayName,
    this.bio,
  });

  factory User.fromDocument(DocumentSnapshot doc){
    return User(
      id: doc['id'],
      email: doc['email'],
      username: doc['username'],
      photoUrl: doc['photoUrl'],
      displayName: doc['displayName'],
      bio: doc['bio'],
    );
  }
}

Firebase 数据库数据截图

Firebase Users Data Screenshot

Answer 1

如果看起来如果实际数据为空，你会得到一个错误。

尝试：

if(!snapshot.hasData || snapshot.data?.documents == null)

代替：

if (!snapshot.hasData)

参考 - https://github.com/flutter/flutter/issues/22199

Answer 2

已解决

在我将 if 语句更改为以下行之后，它正在工作。

if(!snapshot.hasData || snapshot.data.documents == null)