我在飞镖中遇到一个错误，需要你的帮助

Question

我有一个应用程序，我创建了一个登录和注销页面。。。当我点击我的应用程序的注销按钮时，我会得到这样的错误"；对空值使用的空校验运算符"*当我指出错误时，它告诉我[1]：https://i.stack.imgur.com/n0uJ8.pngentrez

导入"dart:async"；导入"dart:convert"；导入"dart:async"；导入"dart:convert"；导入"dart:math"；导入"package:flutter/material.dart"；导入"package:http://dart"；导入'package:logger/logger.dart'；

import '../db/db_auth_shared_preference.dart';
import '../network/app_urls.dart';
import '../models/auth.dart';
enum Status {
notLoggedIn,
loggedIn,
authenticating,
loggedOut,
notReet,
reseted,
resetting
}
//Help display the logs
var logger = Logger();
class AuthProvider with ChangeNotifier {
Auth? _auth;
Auth get auth => _auth!;
void setAuth(Auth auth) {
_auth = auth;
notifyListeners();
}
bool isAuth() {
if (_auth == null || auth.token == '') {
return false;
}
return true;
}
// Time before the token expires
Timer? _authTimer;
DateTime? _expiryDate;
String? username;
String? password;
// Set the status of the user to Not Logged In at the start     of the app
Status _status = Status.notLoggedIn;
Status get status => _status;
// Change the status of the user
set status(Status value) {
_status = value;
notifyListeners();
}
// Log In the user
Future<Map<String, dynamic>> login(String email, String password) async {
Map<String, Object> results;
final Map<String, dynamic> loginData = {
'email': email,
'password': password
};
status = Status.authenticating;
logger.d("--- Authentication ---");
try {
Response response = await post(
Uri.parse(
"${AppUrl.login}?    username=${loginData['email']}&password=${loginData['password']}"    

)，)；

logger.d('Login response : ${response.statusCode}');
// The Request Succeded
if (response.statusCode == 200) {
final Map<String, dynamic> responseData =
json.decode(utf8.decode(response.bodyBytes));
var requestStatus = responseData["status"];
if (requestStatus != 0) {
status = Status.notLoggedIn;
results = {'status': false, 'message': "La Connexion a échoué"};
} else {
// Get the status code of the request
Map<String, dynamic> authData =    responseData["utilisateurJson"];
logger.d(authData);
_expiryDate = DateTime.now().add(const Duration(seconds: 3500));
//store user shared pref
Auth authUser = Auth.fromMap(authData,
timeToExpire: _expiryDate,
username: loginData['email'],
password: loginData['password']);
_expiryDate = authUser.expiryDate;
logger.wtf(_expiryDate);
//clear session data
AuthPreferences().removeAuth();
//store User session
AuthPreferences().saveAuth(authUser);
setAuth(authUser);
status = Status.loggedIn;
username = loginData["email"];
password = loginData["password"];
results = {
'status': true,
'message': 'Successful login',
'auth': authUser,
};
autoLogOut();
}
} else {
status = Status.notLoggedIn;
results = {'status': false, 'message': 'La Connexion a échoué'};
}
return results;
} catch (e) {
logger.e(e);
status = Status.notLoggedIn;
results = {
'status': false,
'message': "La Connexion avec le serveur a échoué"
};
return results;
}   }
void autoLogOut() {
if (_authTimer != null) {
_authTimer!.cancel();
}
final timeToExpiry =        _expiryDate!.difference(DateTime.now()).inSeconds;
_authTimer = Timer(Duration(seconds: timeToExpiry),
() async => await login(username!, password!));
}
// Log Out the User
void logOut() {
logger.d("--- User Logging Out ---");
AuthPreferences().removeAuth();
status = Status.loggedOut;
_expiryDate = null;
_auth = null;
logger.d("--- User Logged Out ---");
}
Future<Auth?> tryAutoLogin() async {
final authSession = await AuthPreferences().getAuth();
if (authSession == null) {
return null;
}
logger.d("The expiry time is : ${authSession.expiryDate}");
if (authSession.expiryDate.isBefore(DateTime.now())) {
login(authSession.username, authSession.password);
return authSession;
}
_expiryDate = authSession.expiryDate;
setAuth(authSession);
logger.d("SETTING THE USER");
autoLogOut();
return authSession;
}
}

Answer 1

错误解释：Bang运算符(！(表示在flutter中，当您使用此运算符时，您完全可以确定变量在任何情况下都不会为null

有两种解决方法-

1. 如果有条件，则使用确认变量不为null
2. 如果运算符为null，则使用null感知或喜欢

Auth get auth => _auth ?? Auth();

由于您没有提供任何错误日志；基于所附的图像，作为第29行上的光标，_auth变量为null。因此，在使用!之前，请确保您的变量不是null。