Question

上下文：

我正在用azure广告构建一个简单的登录应用程序，该应用程序可以很好地登录并获取令牌，然后很好地重定向到下一页，但是在重定向之前会引发错误

错误：

在构建器Builder（dirty，依赖项：[MediaQuery]）：类型'Future'不是以下类型的子类型输入“小部件”

相关的引起错误的小部件是：Builder 文件：/// D：/Projects/flutter/aims_mobile/lib/screens/authentication/signin.dart：101：17 引发异常时，这是堆栈：＃0 _SignInState.build。（package：aims_mobile / screens / authentication / signin.dart：133：25）＃1 Builder.build（package：flutter / src / widgets / basic.dart：7185：48）＃2 StatelessElement.build（package：flutter / src / widgets / framework.dart：4749：28）＃3 ComponentElement.performRebuild（package：flutter / src / widgets / framework.dart：4675：15）＃4 Element.rebuild（package：flutter / src / widgets / framework.dart：4369：5）

代码

class _SignInState extends State<SignIn> {
  static const String SCOPE ='';
  static const String TENANT_ID = 'organizations';
  static String authority = "";

  MsalMobile msal;
  bool isSignedIn = false;

  @override
  void initState() {
    super.initState();
    MsalMobile.create('assets/auth_config.json', authority).then((client) {
      setState(() {
        msal = client;
      });
      refreshSignedInStatus();
    });
  }

  /// Updates the signed in state
  refreshSignedInStatus() {
    msal.getSignedIn().then((loggedIn) {
      print('refreshing');
      setState(() {
        isSignedIn = loggedIn;
      });
    });
  }

  /// Signs a user in
  handleSignIn() async {
    await msal.signIn(null, [SCOPE]).then((result) {
      refreshSignedInStatus();
    }).catchError((exception) {
      if (exception is MsalMobileException) {
        logMsalMobileError(exception);
      } else {
        final ex = exception as Exception;
        print('exception occurred');
        print(ex.toString());
      }
    });
  }

  logMsalMobileError(MsalMobileException exception) {
    print('${exception.errorCode}: ${exception.message}');
    if (exception.innerException != null) {
      print(
          'inner exception = ${exception.innerException.errorCode}: ${exception.innerException.message}');
    }
  }

  /// Signs a user out.
  handleSignOut() async {
    try {
      print('signing out');
      await msal.signOut();
      print('signout done');
      refreshSignedInStatus();
    } on MsalMobileException catch (exception) {
      logMsalMobileError(exception);
    }
  }

  /// Gets the current and prior accounts.
  handleGetAccount() async {
    await msal.getAccount().then((result) {
      if (result.currentAccount != null) {
        print('current account id: ${result.currentAccount.id}');
        print('current account id: ${result.currentAccount.username}');
      } else {
        print('no account found');
      }
    }).catchError((exception) {
      if (exception is MsalMobileException) {
        logMsalMobileError(exception);
      } else {
        print('exception occurred');
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: new Scaffold(
      body: Builder(
        builder: (context) => Stack(
          fit: StackFit.expand,
          children: <Widget>[
            Container(
              width: MediaQuery.of(context).size.width,
              height: MediaQuery.of(context).size.height,
              child: Image.asset('assets/landing.webp',
                  fit: BoxFit.fill,
                  color: Color.fromRGBO(255, 255, 255, 0.6),
                  colorBlendMode: BlendMode.modulate),
            ),
            Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                SizedBox(height: 10.0),
                Container(
                  width: 130.0,
                  child: Align(
                      alignment: Alignment.center,
                      child: RaisedButton(
                        shape: RoundedRectangleBorder(
                            borderRadius: new BorderRadius.circular(30.0)),
                        color: Color(0xffffffff),
                        child: Row(
                          mainAxisAlignment: MainAxisAlignment.start,
                          children: <Widget>[
                            isSignedIn
                                ? Future.delayed(Duration.zero, () {
                                    Navigator.of(context).pushReplacement(
                                        MaterialPageRoute(
                                            builder: (context) => NavScreen()));
                                  })
                                : RaisedButton(
                                    child: Text("Sign In"),
                                    onPressed: handleSignIn,
                                  ),
                          ],
                        ),
                      )),
                )
              ],
            ),
          ],
        ),
      ),
    ));
  }
}

我不知道如何解决这个问题

Answer 1

您传递的是函数Future而不是Widget，这会导致此错误。

isSignedIn
      ? Future.delayed(Duration.zero, () {  // <---- This is not a widget
            Navigator.of(context).pushReplacement(
                MaterialPageRoute(
            builder: (context) => NavScreen()));
        })
        : RaisedButton(
        child: Text("Sign In"),
        onPressed: handleSignIn,
    ),

您可以使用Visibility小部件来隐藏/显示“登录”按钮，而使用bool isSignedIn，可以处理导航代码。

Visibility(
  visible: !isSignedIn,
  child: RaisedButton(
    child: Text("Sign In"),
    onPressed: handleSignIn,
  ),
),

您应该在initState的{{1}}方法内处理导航，如下所示：

StatefulWidget

在构建Builder时引发了以下_TypeError（脏，相关性：[MediaQuery]）：类型'Future <Null>'不是类型'Widget'的子类型

1 个答案: