未使用ChangeNotifier设置用户？

Question

我正在使用块模式进行状态管理，当我使用WPUserInfoResponse方法访问用户数据来设置currentuser时，在我登录并试图访问用户页面上的currentuser时，我仍然得到null。

不断收到错误

   The following NoSuchMethodError was thrown building UserPage(dirty, dependencies: 
   [InheritedProvider<Wordpress>], state: _UserPageState#df273):
   The getter 'username' was called on null.
   Receiver: null
   Tried calling: username
   The relevant error-causing widget was:
   UserPage file:///F:/Flutter/mindmover/lib/providers/wordpress.dart:82:31

Wordpress changenotifier，其中有login和getuser方法，当用户登录到登录页面时会调用它们。我已经检查过currentuser，它不是空的。

enum LoginState { loggedin, signedout }
enum RoleState { admin, mentor, user }
enum ErrorState { invalidParams, serverIssue }

class Wordpress extends ChangeNotifier {
  String userTokenId;
  int errorMessage = 1;
  WPUserInfo.Data currentuser;

  LoginState loginState = LoginState.signedout;

  get isLoggedIn => loginState == LoginState.loggedin;
  get isSignOut => loginState == LoginState.signedout;
  get errorMessageState => errorMessage;
  WPUserInfo.Data get currentUserModel => currentuser;

  dynamic lindawk =
      WPJsonAPI.instance.initWith(baseUrl: "https://www.XXXX.dk");

  Future login(String username, String password, context) async {
    print(username.toString() + password.toString());

    WPUserLoginResponse wpUserLoginResponse = await WPJsonAPI.instance.api(
      (request) {
        return request.wpLogin(
            username: username,
            password: password,
            authType: WPAuthType.WpUsername);
      },
    );

    if (wpUserLoginResponse != null) {
      userTokenId = wpUserLoginResponse.data.userToken;
      loginState = LoginState.loggedin;

      getUser(userTokenId, context);
    } else {
      print("invalid login details");
      errorMessage += 2;
    }
  }

  getUser(String userTokenId, context) async {
    WPUserInfo.WPUserInfoResponse wpUserInfoResponse =
        await WPJsonAPI.instance.api(
      (request) {
        notifyListeners();
        return request.wpGetUserInfo(userTokenId);
      },
    );

    if (wpUserInfoResponse != null) {
      print(wpUserInfoResponse.data.username);
      currentuser = wpUserInfoResponse.data;
      notifyListeners();
      onValidUser(currentuser, context);
    } else {
      wpUserInfoResponse.message.toString();
      errorMessage = 2;
      print("something went wrong");
      //errorMessage = "Something whent wrong";
    }
  }

  void onValidUser(WPUserInfo.Data user, context) {
    print(currentuser);
    Navigator.pushReplacement(
      context,
      MaterialPageRoute(
        builder: (context) => UserPage(
          user: user,
        ),
      ),
    );
  }
}

在wordpress class I user multiple provider中，player类可以正常工作，但MyApp类不能。

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider<Player>.value(
          value: Player(),
        ),
        ChangeNotifierProvider<Wordpress>(
          create: (_) { return Wordpress(); },
          child: AppBottomNavigationBar(),
        )
      ],

在用户页面上，我调用了wordpress类，但是username的值总是空的？

@override
  Widget build(BuildContext context) {
  Wordpress wordpress = Provider.of<Wordpress>(context);

    return Scaffold(
      appBar: AppBar(
        actions: <Widget>[
          FlatButton(
            onPressed: () => {
              Navigator.pushReplacement(
                context,
                MaterialPageRoute(
                  builder: (_) => AppBottomNavigationBar(),
                ),
              ),
            },
            child: Icon(Icons.add_circle_outline),
          ),
        ],
      ),
      body: Container(
        child: Column(
          children: <Widget>[
            FlatButton(
              onPressed: null,
              child: Text(wordpress.currentUserModel.username),
            ),
          ],
        ),
      ),
    );
}

Answer 1

也许把类型给提供者会给你一个实际的Wordpress类，你在调用它之前有没有检查过你的Wordpress类中的currentUserModel是否是非空的？

@override
Widget build(BuildContext context) {
Wordpress wordpress = Provider.of<Wordpress>(context); //Give the type of value the provider should search in the tree

return Scaffold(
  appBar: AppBar(
    actions: <Widget>[
      FlatButton(
        onPressed: () => {
          Navigator.pushReplacement(
            context,
            MaterialPageRoute(
              builder: (_) => AppBottomNavigationBar(),
            ),
          ),
        },
        child: Icon(Icons.add_circle_outline),
      ),
    ],
  ),
  body: Container(
    child: Column(
      children: <Widget>[
        FlatButton(
          onPressed: null,
          child: Text(wordpress.currentUserModel.username), // without the type maybe provider can't give back the class and return null, null.currentUserModel.username gives the error
        ),
      ],
    ),
  ),
);
}