手势捕获的异常。用于空值的空检查运算符

Question

here is the error message from the console

user_provider

import 'package:flutter/material.dart';
import 'package:social_network/models/user.dart';
import 'package:social_network/resources/auth_method.dart';

class UserProvider with ChangeNotifier {
  User? _user;
  final AuthMethods _authMethods = AuthMethods();

  User get getUser => _user!;

  Future<void> refreshUser() async {
    User? user = await _authMethods.getUserDetails();
    _user = user;
    notifyListeners();
  }
}

add_post_screen

import 'dart:typed_data';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:provider/provider.dart';
import 'package:social_network/providers/user_provider.dart';
import 'package:social_network/resources/firestore_methods.dart';
import 'package:social_network/utils/colors.dart';
import 'package:social_network/utils/utils.dart';

class AddPostScreen extends StatefulWidget {
  const AddPostScreen({Key? key}) : super(key: key);

  @override
  _AddPostScreenState createState() => _AddPostScreenState();
}

class _AddPostScreenState extends State<AddPostScreen> {
  Uint8List? _file;
  bool _isLoading = false;
  final TextEditingController _descriptionController = TextEditingController();

  _selectImage(BuildContext parentContext) async {
    return showDialog(
        context: parentContext,
        builder: (BuildContext context) {
          return SimpleDialog(
            title: const Text('Create a post'),
            children: <Widget>[
              SimpleDialogOption(
                padding: const EdgeInsets.all(20),
                child: const Text('Take a photo'),
                onPressed: () async {
                  Navigator.of(context).pop();
                  Uint8List file = await pickImage(ImageSource.camera);
                  setState(() {
                    _file = file;
                  });
                },
              ),
              SimpleDialogOption(
                padding: const EdgeInsets.all(20),
                child: const Text('Choose from gallery'),
                onPressed: () async {
                  Navigator.of(context).pop();
                  Uint8List file = await pickImage(ImageSource.gallery);
                  setState(() {
                    _file = file;
                  });
                },
              ),
              SimpleDialogOption(
                padding: const EdgeInsets.all(20),
                child: const Text('Cancel'),
                onPressed: () {
                  Navigator.of(context).pop();
                },
              ),
            ],
          );
        });
  }

  void postImage(
    String uid,
    String username,
    String profileImage,
  ) async {
    setState(() {
      _isLoading = true;
    });
    try {
      String res = await FirestoreMethods().uploadPost(
          _descriptionController.text, _file!, uid, username, profileImage);
      if (res == "Succes") {
        setState(() {
          _isLoading = false;
        });
        showSnackBar('Posted!', context);
        clearImage();
      } else {
        showSnackBar(res, context);
      }
    } catch (e) {
      setState(() {
        _isLoading = false;
      });
      showSnackBar(e.toString(), context);
    }
  }

  void clearImage() {
    setState(() {
      _file = null;
    });
  }

  @override
  void dispose() {
    super.dispose();
    _descriptionController.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final UserProvider userProvider = Provider.of<UserProvider>(context);
    return _file == null
        ? Center(
            child: IconButton(
              icon: const Icon(Icons.upload),
              onPressed: () => _selectImage(context),
            ),
          )
        : Scaffold(
            appBar: AppBar(
              backgroundColor: mobileBackgroundColor,
              leading: IconButton(
                icon: const Icon(Icons.arrow_back),
                onPressed: clearImage,
              ),
              title: const Text('Post to'),
              centerTitle: false,
              actions: <Widget>[
                TextButton(
                  onPressed: () => postImage(
                    userProvider.getUser.uid,
                    userProvider.getUser.username,
                    userProvider.getUser.photoUrl,
                  ),
                  child: const Text(
                    'Post',
                    style: TextStyle(
                      color: Colors.redAccent,
                      fontWeight: FontWeight.bold,
                      fontSize: 18,
                    ),
                  ),
                ),
              ],
            ),
            body: Column(
              children: [
                _isLoading
                    ? const LinearProgressIndicator()
                    : const Padding(
                        padding: EdgeInsets.only(top: 0),
                      ),
                const Divider(),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceAround,
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    CircleAvatar(
                      backgroundImage: NetworkImage(
                        'https://images.unsplash.com/photo-1522441815192-d9f04eb0615c?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=654&q=80',

    //   userProvider.getUser.photoUrl,
                      ),
                    ),
                    SizedBox(
                      width: MediaQuery.of(context).size.width * 0.4,
                      child: TextField(
                        controller: _descriptionController,
                        decoration: const InputDecoration(
                          hintText: 'Write a caption...',
                          border: InputBorder.none,
                        ),
                        maxLines: 8,
                      ),
                    ),
                    SizedBox(
                      height: 45,
                      width: 45,
                      child: AspectRatio(
                        aspectRatio: 487 / 451,
                        child: Container(
                          decoration: BoxDecoration(
                            image: DecorationImage(
                              image: MemoryImage(_file!),
                              fit: BoxFit.fill,
                              alignment: FractionalOffset.topCenter,
                            ),
                          ),
                        ),
                      ),
                    ),
                    const Divider(),
                  ],
                )
              ],
            ));
  }
}

auth_methods.dart

import 'dart:typed_data';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:social_network/models/user.dart' as model;
import 'package:social_network/resources/storage_methods.dart';

class AuthMethods {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;

  Future<model.User?> getUserDetails() async {
    User currentUser = _auth.currentUser!;

    DocumentSnapshot documentSnapshot =
        await _firestore.collection('user').doc(currentUser.uid).get();

    return model.User.fromSnap(documentSnapshot);
  }

  //sign up the user
  Future<String> signUpUser({
    required String email,
    required String password,
    required String username,
    required String bio,
    required Uint8List? file,
  }) async {
    String res = "Some error occurred";
    try {
      if (email.isNotEmpty ||
          password.isNotEmpty ||
          username.isNotEmpty ||
          bio.isNotEmpty ||
          file != null) {
        //register the user
        UserCredential cred = await _auth.createUserWithEmailAndPassword(
            email: email, password: password);

        String photoUrl = await StorageMethods()
            .uploadImageToStorage('profilePictures', file!, false);

        //adding user to our database

        model.User _user = model.User(
          bio: bio,
          username: username,
          uid: cred.user!.uid,
          email: email,
          photoUrl: photoUrl,
          following: [],
          followers: [],
        );

        await _firestore.collection("users").doc(cred.user!.uid).set(
              _user.toJson(),
            );
        res = "Succes";
      } else {
        res = "Please enter all the fields";
      }
    } catch (err) {
      res = err.toString();
    }
    return res;
  }

// logging the user
  Future<String> loginUser(
      {required String email, required String password}) async {
    String res = "Some error occured";
    try {
      if (email.isNotEmpty || password.isNotEmpty) {
        await _auth.signInWithEmailAndPassword(
            email: email, password: password);
        res = "Succes";
      } else {
        res = "Please enter all the fields required";
      }
    } catch (err) {
      res = err.toString();
    }
    return res;
  }
}

你好。我将尝试制作一个发布按钮，当我尝试上传照片并按下发布按钮时，我收到此错误。

您对此错误有任何解决方案吗？非常感谢！

错误信息：

在 474 毫秒内重新启动应用程序。 [VERBOSE-2:ui_dart_state.cc(198)] 未处理的异常：类型“Null”不是类型转换中“Map”类型的子类型

════════手势捕捉到异常═════════════════════════════␕══ ════════ 用于空值的空检查运算符 ══════════════════════════════════════════════════ ══════════════════════════════ [VERBOSE-2:profiler_metrics_ios.mm(203)] 检索线程信息时出错：(os/kern) 对象终止

Answer 1

我相信你的问题在

onPressed: () => postImage(
                userProvider.getUser.uid,
                userProvider.getUser.username,
                userProvider.getUser.photoUrl,
              ),

在调用方法之前确保用户不为空， 发布更多代码会更有帮助_authMethods.getUserDetails();这个方法里面有什么？

---

更新：

Future<model.User?> getUserDetails() async {
    User currentUser = _auth.currentUser!;

    DocumentSnapshot documentSnapshot =
    await _firestore.collection('user').doc(currentUser.uid).get();

    //add the following lines
    print('documentSnapshot: $documentSnapshot');
    if(documentSnapshot == null) return null;

    return model.User.fromSnap(documentSnapshot);
}