Error Im getting is - Null Function(DataSnapshot) can;t be assigned to the parameter type 'Futu-CodePudding

Error Im getting is - Null Function(DataSnapshot) can;t be assigned to the parameter type 'FutureOr Function(DatabaseEvent)'Im trying to retrieve data from firebase but it is not happening.

    import 'package:flutter/material.dart';
    import 'package:firebase_database/firebase_database.dart';
    import 'package:firebase_core/firebase_core.dart';
    import 'package:firebase_auth/firebase_auth.dart';
    
    class HomePage extends StatefulWidget {
      @override
      _HomePageState createState() => _HomePageState();
    }
    
    class _HomePageState extends State<HomePage> {
    
      final textcontroller = TextEditingController();
      final databaseRef = FirebaseDatabase.instance.reference();
      final Future<FirebaseApp> _future = Firebase.initializeApp();
      //FirebaseAuth auth = FirebaseAuth.instance;
    
    
    
    
      void addData(String data) {
        databaseRef.child("Valve").set({Flow : 'ON'});
      }
      void addData2(String data) {
        databaseRef.child("Valve").set({Flow : 'OFF'});
      }
    
    
    
      void ReadData_once() {
        databaseRef.child("FirebaseIOT").child("LatestReading").once().then((DataSnapshot Snapshot) {
          print();
    
        });//this is the error
      }
    
      void printFirebase(){
        databaseRef.once().then((DataSnapshotsnapshot) {
    
          print('Data : ');
        });
      }//this is where error is coming

CodePudding user response：

Instead of DataSnapshot, you should put DatabaseEvent within the then

So this part

databaseRef.child("FirebaseIOT").child("LatestReading").once().then((DataSnapshot Snapshot) {print('test')}

should be

databaseRef.child("FirebaseIOT").child("LatestReading").once().then((DatabaseEvent event) {print('test')}

CodePudding user response：

I am not a dart/flutter programmer but i know that you have to initialize app before any other modules you want to use from firebase library.

So try to switch this lines:

final Future<FirebaseApp> _future = Firebase.initializeApp();
final databaseRef = FirebaseDatabase.instance.reference();

And i'm pretty sure initializeApp() needs firebase config object so you should initialize like this: firebase.initializeApp(firebaseConfig).

I don't know what is this: Future<FirebaseApp> why you force to get initialization result to be this future generic object ?