NoSuchMethodError: 在 null 上调用了方法“[]”接收器：空尝试调用：[](“duyuru”)

如何解决NoSuchMethodError: 在 null 上调用了方法“[]”接收器：空尝试调用：[](“duyuru”)

//我的duyuru控制器

class DuyuruController extends GetxController {
  FirebaseFirestore _firebaseFirestore = FirebaseFirestore.instance;
  TextEditingController duyuru = TextEditingController();
  Rx<List<DuyuruModel>> duyurumodel = Rx<List<DuyuruModel>>([]);
  List<DuyuruModel> get newsModelList => duyurumodel.value;
  @override
  void onInit() {
    duyurumodel.bindStream(todoStream(uid));
    super.onInit();
  }

  var uid;
  String collection = "duyuru";

  firestoreduyuruekle(String id) {
    uid = new Uuid().v4().toString();
    _firebaseFirestore.collection(collection).doc(uid).set({
      "kullaniciid": id,"duyuruid": uid,"duyuru": duyuru.text,});

    duyuru.clear();
  }

  Stream<List<DuyuruModel>> todoStream(String uid) {
    return _firebaseFirestore
        .collection(collection)
        .doc(uid)
        .snapshots()
        .map((query) {
      var data = query.data();
      List veriler = data['duyuru'];
      List<DuyuruModel> retVal = [];
      veriler.forEach((element) {
        retVal.add(DuyuruModel.fromMap(element));
      });
      return retVal;
    });
  }
}

// 我的模型

class DuyuruModel {
  static const ID = "duyuruid";
  static const NAME = "duyuru";

  String id;
  String duyuru;

  DuyuruModel({
    this.id,this.duyuru,});

  DuyuruModel.fromMap(DocumentSnapshot documentSnapshot) {
    id = (documentSnapshot.data() as Map)[ID];
    duyuru = (documentSnapshot.data() as Map)[NAME];
  }
}

// 我的用户界面

 class DuyuruWidget extends StatefulWidget {
  @override
  _DuyuruWidgetState createState() => _DuyuruWidgetState();
}

class _DuyuruWidgetState extends State<DuyuruWidget> {
  var deger2 = Get.put<AuthController>(AuthController());
  var deger1 = Get.put<DuyuruController>(DuyuruController());

  @override
  Widget build(BuildContext context) {
    return Obx(() {
      if (deger1.newsModelList == null) {
        return Text('Loading');
      } else if (deger1.newsModelList.isEmpty) {
        return Text('Empty List');
      } else {
        return ListView.builder(
          itemCount: deger1.newsModelList.length,itemBuilder: (context,index) {
            return Text(deger1.newsModelList[index].duyuru);
          },);
      }
    });
  }
}

// addDuyuru

class DuyuruEklemeSayfasi extends StatelessWidget {
  var deger = Get.put(DuyuruController());
  var kontrol = Get.put(AuthController());
  final GlobalKey<FormState> control = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Duyuru Ekle"),),body: Container(
        child: Form(
          key: control,child: Column(
            children: [
              TextFormField(
                validator: (value) {
                  if (value == null && value.isEmpty) {
                    Get.snackbar("Hata","Lütfen Duyuru giriniz");
                  }
                  return;
                },controller: deger.duyuru,decoration: Inputdecoration(
                  hintText: "Duyuru Ekle",ElevatedButton(
                onpressed: () {
                  deger.firestoreduyuruekle(kontrol.usermodel.value.id);
                  Get.to(HomeScreen());
                },child: Text("Duyuruyu Ekle"),],);
  }
}

// Duyuruwidget

class DuyuruWidget extends StatefulWidget {
  @override
  _DuyuruWidgetState createState() => _DuyuruWidgetState();
}

class _DuyuruWidgetState extends State<DuyuruWidget> {
  var deger2 = Get.put<AuthController>(AuthController());
  var deger1 = Get.put<DuyuruController>(DuyuruController());

  @override
  Widget build(BuildContext context) {
    return Obx(() {
      if (deger1.newsModelList == null) {
        return Text('Loading');
      } else if (deger1.newsModelList.isEmpty) {
        return Text('Empty List');
      } else {
        return ListView.builder(
          itemCount: deger1.newsModelList.length,index) {
            return Text(
              deger1.newsModelList[index].duyuru,style: TextStyle(color: Colors.black),);
          },);
      }
    });
  }
}

// 用户控制器

class AuthController extends GetxController {
  FirebaseAuth auth = FirebaseAuth.instance;
  FirebaseFirestore _firebaseFirestore = FirebaseFirestore.instance;

  TextEditingController emailtext = TextEditingController();
  TextEditingController password = TextEditingController();
  Rx<User> user;
  Rx<usermodel> usermodel = usermodel().obs;

  String usercollection = "users";
  String duyurucollection = "duyuru";

  @override
  void onReady() {
    user = Rx<User>(auth.currentUser);
    user.bindStream(auth.userChanges());
    ever(user,setscreen);

    super.onReady();
  }

  setscreen(User user) {
    if (user == null) {
      Get.to(AuthenScreen());
    } else {
      usermodel.bindStream(listentouser());
      Get.to(HomeScreen());
    }
  }

  void signIn() async {
    try {
      await auth
          .signInWithEmailAndPassword(
              email: emailtext.text.trim(),password: password.text.trim())
          .then((result) {
        _clearControllers();
      });
    } catch (e) {
      debugPrint(e.toString());
      Get.snackbar("Sign In Failed","Try again");
    }
  }

  void signUp() async {
    try {
      await auth
          .createuserWithEmailAndPassword(
              email: emailtext.text.trim(),password: password.text.trim())
          .then((result) {
        String _userId = result.user.uid;
        _addUserToFirestore(_userId);
        _clearControllers();
      });
    } catch (e) {
      debugPrint(e.toString());
      Get.snackbar("Sign In Failed","Try again");
    }
  }

  void signOut() async {
    await auth.signOut();
  }

  void _addUserToFirestore(String userId) {
    _firebaseFirestore.collection(usercollection).doc(userId).set({
      "password": password.text.trim(),"id": userId,"email": emailtext.text.trim(),});
  }

  Stream<usermodel> listentouser() {
    return _firebaseFirestore
        .collection(usercollection)
        .doc(user.value.uid)
        .snapshots()
        .map((event) => usermodel.fromSnapshot(event));
  }

  void _clearControllers() {
    emailtext.clear();
    password.clear();
  }
}

我的错误：未处理的异常：NoSuchMethodError：方法“[]”被调用为空值。接收器：空。尝试调用：。即使我检查为空，列表也是空的，你能帮我吗？我无法解决。

我的 firestore duyuru 数据库

我的 Firestore 用户数据库

我收到列表空检查错误，但我的数据库中有公告数据，我正在提取它们，但在屏幕上看不到数据