Firebase 调用异常

Question

我正在尝试使用 Firebase 制作简单的登录逻辑，但无法摆脱此错误：

Exception has occurred.
DartError: Bad state: Cannot fire new event. Controller is already firing an event

这是我的代码：

import 'package:firebase_database/firebase_database.dart';
import 'package:flutter/material.dart';
import 'package:identity_retro/models/user_model.dart';
import 'package:uuid/uuid.dart';

class DatabaseOperations {
  static final FirebaseDatabase database = FirebaseDatabase.instance;
  DatabaseReference ref = FirebaseDatabase.instance.ref();

  Future<UserModel?> getUserByEmail(String username) async {
    var response = await ref
        .child('users')
        .orderByChild('username')
        .equalTo(username)
        .once();

    if (!response.snapshot.exists) {
      return null;
    }

    var userMap = Map<String, dynamic>.from(response.snapshot.value as Map);
    var user =
        UserModel.fromJson(userMap);

    return user;
  }

  Future<UserModel?> getUserById(String id) async {
    var response =
        await ref.child('users').orderByChild('id').equalTo(id).once();

    if (!response.snapshot.exists) {
      return null;
    }

    var user =
        UserModel.fromJson(response.snapshot.value as Map<String, dynamic>);

    return user;
  }

  Future<bool> addUser(UserModel user, BuildContext context) async {
    if (await getUserByEmail(user.username!) != null)
    {
      if (context.mounted) {
        await showDialog(
            context: context,
            builder: (BuildContext context) {
              return AlertDialog(
                title: const Text('Error'),
                content: const Text('User already exists'),
                actions: <Widget>[
                  TextButton(
                    onPressed: () {
                      Navigator.of(context).pop();
                    },
                    child: const Text('OK'),
                  ),
                ],
              );
            });
      }

      return false;
    }

    var id = Uuid().v4();

    await ref.child('users/$id').set({'username': user.username, 'password': user.password});

    return await getUserById(id) != null;
  }
}

当用户不存在并且尝试在这一行中创建新用户时，在积极的情况下会发生异常：

await ref.child('users/$id').set({'username': user.username, 'password': user.password});

Stacktrace 指向database_reference_web.dart 文件第51 行。这是一个set 方法

但值得一提的是，尽管用户最终还是创建了错误

Answer 1

似乎您尝试在流/控制器仍在处理先前的事件时更新或读取数据

试试这个代码

Future<bool> addUser(UserModel user, BuildContext context) async {
  // Check if the user already exists by username
  if (await getUserByEmail(user.username!) != null) {
    if (context.mounted) {
      // Display an error dialog if the user exists
      await showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: const Text('Error'),
            content: const Text('User already exists'),
            actions: <Widget>[
              TextButton(
                onPressed: () {
                  Navigator.of(context).pop();
                },
                child: const Text('OK'),
              ),
            ],
          );
        },
      );
    }
    return false;
  }

  // Generate a unique ID for the user
  var id = Uuid().v4();

  // Add the user to the Firebase database
  await ref.child('users/$id').set({
    'id': id, // Ensure that you store the ID in the user object
    'username': user.username,
    'password': user.password,
  });

  // Retrieve the user by ID to confirm the insertion
  var addedUser = await getUserById(id);
  return addedUser != null;
}

如果仍然遇到任何问题，请尝试实现 try catch 并使用断点进行调试