来自 Firebase auth 或 sharedpreference 的 Flutter 更新变量

Question

我几乎迷路了我已经为此工作了好几天，我有一个 Text() 小部件并在其中传递了一个变量，该变量包含来自 Firebase auth 的用户名。问题是我想检查用户是否登录。如果用户登录，我可以从 Firebase 完成用户名，但在未登录时它会崩溃我已经尝试使用共享首选项和 Firebase 当前用户，但它仍然无法正常工作。 我尝试过的：

    class _HomePageState extends State<HomePage> {

  String username = 'user name';
  String userEmail = 'email address';

  @override
  void initState() {
    super.initState();
    getCurrentUserName().then((value) {
      username = value;
    });
    getLanguage();
  }

  String language;
  var refreshKey = GlobalKey<RefreshIndicatorState>();
  Map data;

  String news;
  String signIn;
  List<Tab> tabs;
  ListView sideBarTabs;

  Future<String> getCurrentUserName() {
    return new Future<String>.delayed(new Duration(milliseconds: 10000),() async {
      //Do a long running task. E.g. Network Call.
      final FirebaseUser currentUser = await _auth.currentUser();
      //assert(user.uid == currentUser.uid);

      username = currentUser.displayName;
      return username;
    });
  }

  Future getLanguage() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    int lang = prefs.getInt('Language');

    setState(() {
      if (lang != 1) {
        language = 'ku';
        news = 'هه‌وا';
        signIn = 'بچۆ ژووره‌وه‌';
        sideBarTabs = ListView(
          children: <Widget>[
            new UserAccountsDrawerHeader(
              accountName: Text(username),
              accountEmail: Text(userEmail),
              currentAccountPicture: GestureDetector(
                child: new CircleAvatar(
                  backgroundColor: Colors.black,
                  child: Icon(Icons.person),
                ),
              ),
              decoration: new BoxDecoration(
                color: Colors.pink,
              ),
            ),
            InkWell(
                onTap: () {
                  var route = new MaterialPageRoute(
                    builder: (BuildContext context) => new HomePage(),
                  );
                  Navigator.of(context).push(route);
                },
                child: ListTile(
                  title: Text(news),
                  leading: Icon(Icons.featured_play_list),
                )),
            InkWell(
                onTap: () {
                  _SignInWithGoogle();
                },
                child: ListTile(
                  title: Text(signIn),
                  leading: Icon(Icons.person),
                )),
          ],
        );
      } else{
        language = 'ar';
        news = 'أخبار';
        signIn = 'تسجيل الدخول';
        sideBarTabs = ListView(
          children: <Widget>[
            new UserAccountsDrawerHeader(
              accountName: Text(username),
              accountEmail: Text(userEmail),
              currentAccountPicture: GestureDetector(
                child: new CircleAvatar(
                  backgroundColor: Colors.black,
                  child: Icon(Icons.person),
                ),
              ),
              decoration: new BoxDecoration(
                color: Colors.pink,
              ),
            ),
            InkWell(
                onTap: () {
                  var route = new MaterialPageRoute(
                    builder: (BuildContext context) => new HomePage(),
                  );
                  Navigator.of(context).push(route);
                },
                child: ListTile(
                  title: Text(news),
                  leading: Icon(Icons.featured_play_list),
                )),
            InkWell(
                onTap: () {
                  _SignInWithGoogle();
                },
                child: ListTile(
                  title: Text(signIn),
                  leading: Icon(Icons.person),
                )),
          ],
        );
      }
    });
  }

  Future<String> _SignInWithGoogle() async {
    final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth =
    await googleUser.authentication;
    final AuthCredential credential = GoogleAuthProvider.getCredential(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );
    final FirebaseUser user = await _auth.signInWithCredential(credential);
    assert(user.email != null);
    assert(user.displayName != null);
    assert(!user.isAnonymous);
    assert(await user.getIdToken() != null);

    final FirebaseUser currentUser = await _auth.currentUser();
    assert(user.uid == currentUser.uid);

    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setString('username', user.displayName);
    prefs.setString('useremail', user.email);
    //prefs.setString('IdToken', await user.getIdToken());
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: DefaultTabController(
        length: 9,
        child: Scaffold(
        appBar: new AppBar(
        bottom: TabBar(
        labelColor: Colors.black,
        isScrollable: true,
        tabs: tabs,
      ),
      iconTheme: new IconThemeData(color: Colors.black),
      backgroundColor: Colors.white,
      title: Text(
        "App Name",
        style: TextStyle(color: Colors.black),
      ),
    ),
    drawer: new Drawer(
    child: sideBarTabs,
    ),

并具有共享偏好：

class _HomePageState extends State<HomePage> {

  String username = 'user name';
  String userEmail = 'email address';

  @override
  void initState() {
    super.initState();
    getCurrentUserName().then((value) {
      username = value;
    });
    getLanguage();
  }

  String language;
  var refreshKey = GlobalKey<RefreshIndicatorState>();
  Map data;

  String news;
  String signIn;
  List<Tab> tabs;
  ListView sideBarTabs;

  Future<String> getCurrentUserName() {
    return new Future<String>(() async{
      //Do a long running task. E.g. Network Call.
      SharedPreferences prefs = await SharedPreferences.getInstance();

      username = prefs.getString('username');
      return username;
    });
  }

  Future getLanguage() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    int lang = prefs.getInt('Language');

    setState(() {
      if (lang != 1) {
        language = 'ku';

        news = 'هه‌وا';
        signIn = 'بچۆ ژووره‌وه‌';

        sideBarTabs = ListView(
          children: <Widget>[
            new UserAccountsDrawerHeader(
              accountName: Text(username),
              accountEmail: Text(userEmail),
              currentAccountPicture: GestureDetector(
                child: new CircleAvatar(
                  backgroundColor: Colors.black,
                  child: Icon(Icons.person),
                ),
              ),
              decoration: new BoxDecoration(
                color: Colors.pink,
              ),
            ),
            InkWell(
                onTap: () {
                  var route = new MaterialPageRoute(
                    builder: (BuildContext context) => new HomePage(),
                  );
                  Navigator.of(context).push(route);
                },
                child: ListTile(
                  title: Text(news),
                  leading: Icon(Icons.featured_play_list),
                )),
            InkWell(
                onTap: () {
                  _SignInWithGoogle();
                },
                child: ListTile(
                  title: Text(signIn),
                  leading: Icon(Icons.person),
                )),
          ],
        );
      } else{
        language = 'ar';
        news = 'أخبار';
        signIn = 'تسجيل الدخول';
        sideBarTabs = ListView(
          children: <Widget>[
            new UserAccountsDrawerHeader(
              accountName: Text(username),
              accountEmail: Text(userEmail),
              currentAccountPicture: GestureDetector(
                child: new CircleAvatar(
                  backgroundColor: Colors.black,
                  child: Icon(Icons.person),
                ),
              ),
              decoration: new BoxDecoration(
                color: Colors.pink,
              ),
            ),
            InkWell(
                onTap: () {
                  var route = new MaterialPageRoute(
                    builder: (BuildContext context) => new HomePage(),
                  );
                  Navigator.of(context).push(route);
                },
                child: ListTile(
                  title: Text(news),
                  leading: Icon(Icons.featured_play_list),
                )),
            InkWell(
                onTap: () {
                  _SignInWithGoogle();
                },
                child: ListTile(
                  title: Text(signIn),
                  leading: Icon(Icons.person),
                )),
          ],
        );
      }
    });
  }

  Future<String> _SignInWithGoogle() async {
    final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth =
    await googleUser.authentication;
    final AuthCredential credential = GoogleAuthProvider.getCredential(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );
    final FirebaseUser user = await _auth.signInWithCredential(credential);
    assert(user.email != null);
    assert(user.displayName != null);
    assert(!user.isAnonymous);
    assert(await user.getIdToken() != null);

    final FirebaseUser currentUser = await _auth.currentUser();
    assert(user.uid == currentUser.uid);

    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setString('username', user.displayName);
    prefs.setString('useremail', user.email);
    //prefs.setString('IdToken', await user.getIdToken());
  }


  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: DefaultTabController(
        length: 9,
        child: Scaffold(
        appBar: new AppBar(
        bottom: TabBar(
        labelColor: Colors.black,
        isScrollable: true,
        tabs: tabs,
      ),
      iconTheme: new IconThemeData(color: Colors.black),
      backgroundColor: Colors.white,
      title: Text(
        "App Name",
        style: TextStyle(color: Colors.black),
      ),
    ),
    drawer: new Drawer(
    child: sideBarTabs,
    ),

还有：

class _HomePageState extends State<HomePage> {

  String username = 'user name';
  String userEmail = 'email address';

  @override
  void initState() {
    super.initState();
    getCurrentUser();
    getLanguage();
  }

  String language;
  var refreshKey = GlobalKey<RefreshIndicatorState>();
  Map data;

  String news;
  String signIn;
  List<Tab> tabs;
  ListView sideBarTabs;

  Future<void> getCurrentUser() async{
    SharedPreferences prefs = await SharedPreferences.getInstance();

    setState(() {
      if (_auth.currentUser() != null) {
        username = prefs.getString('username');
        userEmail = prefs.getString('useremail');
      } else{
        username = 'App name';
        userEmail = 'test@app.com';
      }
    });
  }

  Future getLanguage() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    int lang = prefs.getInt('Language');

    setState(() {
      if (lang != 1) {
        language = 'ku';
        news = 'هه‌وا';
        signIn = 'بچۆ ژووره‌وه‌';
        sideBarTabs = ListView(
          children: <Widget>[
            new UserAccountsDrawerHeader(
              accountName: Text(username),
              accountEmail: Text(userEmail),
              currentAccountPicture: GestureDetector(
                child: new CircleAvatar(
                  backgroundColor: Colors.black,
                  child: Icon(Icons.person),
                ),
              ),
              decoration: new BoxDecoration(
                color: Colors.pink,
              ),
            ),
            InkWell(
                onTap: () {
                  var route = new MaterialPageRoute(
                    builder: (BuildContext context) => new HomePage(),
                  );
                  Navigator.of(context).push(route);
                },
                child: ListTile(
                  title: Text(news),
                  leading: Icon(Icons.featured_play_list),
                )),
            InkWell(
                onTap: () {
                  _SignInWithGoogle();
                },
                child: ListTile(
                  title: Text(signIn),
                  leading: Icon(Icons.person),
                )),
          ],
        );
      } else{
        language = 'ar';
        news = 'أخبار';
        signIn = 'تسجيل الدخول';
        sideBarTabs = ListView(
          children: <Widget>[
            new UserAccountsDrawerHeader(
              accountName: Text(username),
              accountEmail: Text(userEmail),
              currentAccountPicture: GestureDetector(
                child: new CircleAvatar(
                  backgroundColor: Colors.black,
                  child: Icon(Icons.person),
                ),
              ),
              decoration: new BoxDecoration(
                color: Colors.pink,
              ),
            ),
            InkWell(
                onTap: () {
                  var route = new MaterialPageRoute(
                    builder: (BuildContext context) => new HomePage(),
                  );
                  Navigator.of(context).push(route);
                },
                child: ListTile(
                  title: Text(news),
                  leading: Icon(Icons.featured_play_list),
                )),
            InkWell(
                onTap: () {
                  _SignInWithGoogle();
                },
                child: ListTile(
                  title: Text(signIn),
                  leading: Icon(Icons.person),
                )),
          ],
        );
      }
    });

  }

  Future<String> _SignInWithGoogle() async {
    final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth =
    await googleUser.authentication;
    final AuthCredential credential = GoogleAuthProvider.getCredential(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );
    final FirebaseUser user = await _auth.signInWithCredential(credential);
    assert(user.email != null);
    assert(user.displayName != null);
    assert(!user.isAnonymous);
    assert(await user.getIdToken() != null);

    final FirebaseUser currentUser = await _auth.currentUser();
    assert(user.uid == currentUser.uid);

    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setString('username', user.displayName);
    prefs.setString('useremail', user.email);
    //prefs.setString('IdToken', await user.getIdToken());
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: DefaultTabController(
        length: 9,
        child: Scaffold(
        appBar: new AppBar(
        bottom: TabBar(
        labelColor: Colors.black,
        isScrollable: true,
        tabs: tabs,
      ),
      iconTheme: new IconThemeData(color: Colors.black),
      backgroundColor: Colors.white,
      title: Text(
        "App Name",
        style: TextStyle(color: Colors.black),
      ),
    ),
    drawer: new Drawer(
    child: sideBarTabs,
    ),

我知道我的代码有点复杂，因为我的标签是动态的，这就是问题所在，但我需要它。问题是应用程序运行时的用户名变量，而应用程序名称即使用户登录与否，或者在我上面的一些代码中，当用户登录时显示名称或用户尚未登录，应用程序崩溃。

Answer 1

您的代码不可读，但如果您需要知道是否有用户已登录，然后构建您的 UI 元素，您应该使用 FutureBuilder 来完成此操作。

一个sn-p是：

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<FirebaseUser>(
      future: FirebaseAuth.instance.currentUser(),
      builder: (BuildContext context, AsyncSnapshot<FirebaseUser> snapshot){
        if (snapshot.hasData){
          //then there is user logged, so you return your layout here..
          var user = snapshot.data; // this returns you logged firebase user

          return MyWidgetForLoggedUsers( user );
        }

        // so there is no user logged
        return Container(
          child: Text("There is no user active"),
        );

      },
    );
  }

在构建器中，您可以使用snapshot.connectionState 进行更精细的控制。其他选项是使用具有相同原理的 StreamBuilder