当 FirebaseAuth 实例启动时，它会在 Flutter 表单上出错

问题描述

这是我的第一个 Flutter 项目，我对某些事情感到困惑。我创建了这个表单，每当我启动 Firebase 实例时，表单就会消失。

如果我删除此代码 final FirebaseAuth _firebaseAuth = FirebaseAuth.instance; 它工作正常，表单将显示但如果取消注释表单消失并返回此错误：

用于空值的空检查运算符

代码：

import 'package:firebase_auth/firebase_auth.dart';
import 'package:Flutter/material.dart';
import 'package:Flutter/cupertino.dart';
import 'dart:core';
import 'package:email_validator/email_validator.dart';

class CreateLogin extends StatefulWidget {

  final Function goToHomePage;
  CreateLogin({this.goToHomePage});

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

class _CreateLoginState extends State<CreateLogin> {
  bool _termsAgreed = false;
  String email,password,confirmPassword;
  bool saveAttempted = false;
  final formKey = GlobalKey<FormState>();
  final FirebaseAuth _firebaseAuth = FirebaseAuth.instance;

  void _createuser({String email,String password}) {
    _firebaseAuth.createuserWithEmailAndPassword(email: email,password: password).then((authResult) {
       print(authResult.user);
     }).catchError((error){
       print(error);
     });
  }

  @override
  Widget build(BuildContext context) {
    return Form(
      key: formKey,child: Container(
        child: Column(
          children: <Widget>[
            Text('SIGN UP',style: TextStyle(color: Colors.white,fontWeight: FontWeight.w600,fontSize: 26.0),),SizedBox(height: 5,TextFormField( autovalidate: saveAttempted,autovalidateMode: AutovalidateMode.always,validator: (emailValue) {
              if(emailValue.isEmpty){
                return "This email field cannot be empty";
              }return null;
            },onChanged: (textVlaue) {
                setState(() {
                  email = textVlaue;
                });
              },decoration: Inputdecoration(errorStyle: TextStyle(color: Colors.white),hintText: 'Enter Email',hintStyle: TextStyle(color: Colors.white.withOpacity(0.6)),border: UnderlineInputBorder(
                borderSide: BorderSide(color: Colors.white),)),style: TextStyle(fontSize: 22,color: Colors.white),validator: (password) {
              if(password.isEmpty){
                return "This email field cannot be empty";
              } if(password.length < 8){
                return "Password must be greater han 8 character";
              } if(EmailValidator.validate(email) != true){
                return "Invalid email";
              }return null;
            },onChanged: (textVlaue) {
                setState(() {
                  password = textVlaue;
                });
              },obscureText: true,hintText: 'Enter Password',validator: (confirmPassword) {
              if(confirmPassword.isEmpty){
                return "This email field cannot be empty";
              } if (confirmPassword != password) {
                return "It must match password";
              }   return null;
            },onChanged: (textVlaue) {
              setState(() {
                confirmPassword = textVlaue;
              });
              },hintText: 'Comfirm Password',Row(
              children: <Widget>[CheckBox(activeColor: Colors.orange,value: _termsAgreed,onChanged: (newValue) {
                setState(() {
                  _termsAgreed = newValue;
                });
              },Text('Terms & Conditions',fontSize: 16.0),)],Row(
              mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[
                InkWell( onTap: (){ widget.goToHomePage(); },child: Text('CANCEL',fontSize: 20,fontWeight: FontWeight.bold),SizedBox(width: 38,InkWell(
                  onTap: () {
                    setState(() {
                      saveAttempted = true;
                    });
                    if(formKey.currentState.validate()) {
                      formKey.currentState.save();
                      // _createuser(email: email,password: password);
                    }
                  },child: Container(
                    padding: EdgeInsets.symmetric(vertical: 16.0,horizontal: 34.0),decoration: Boxdecoration(
                        color: Colors.white,borderRadius: BorderRadius.circular(30.0),child: Text('SAVE',style: TextStyle(color: Colors.red,],Text('Agree to Terms & Conditions',fontSize: 12),);
  }
}

解决方法

检查您是否在项目中正确初始化了 firebase

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}