I am trying to get multiple nested data from firebase but getting this hashmap error

Question

   ListView listView;
   FirebaseDatabase firebaseDatabase;
   DatabaseReference databaseReference;
   ArrayList<String> arrayList = new ArrayList<>();
   ArrayAdapter<String> arrayAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    firebaseDatabase = FirebaseDatabase.getInstance();
    databaseReference = firebaseDatabase.getReference("Users");


    listView = (ListView) findViewById(R.id.listview);

       Toast.makeText(this, "ok", Toast.LENGTH_SHORT).show();
        databaseReference.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            Log.i( "he","Reference : " + databaseReference.toString() );
            String value = dataSnapshot.getValue(String.class);
            arrayList.add(value);
            arrayAdapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, arrayList);
            listView.setAdapter(arrayAdapter);

        }

This is the error I'am getting:

com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String at com.google.android.gms.internal.firebase_database.zzkt.zzb(Unknown Source) at com.google.android.gms.internal.firebase_database.zzkt.zza(Unknown Source) at com.google.firebase.database.DataSnapshot.getValue(Unknown Source) at com.example.test.MainActivity$1.onChildAdded(MainActivity.java:86) at com.google.android.gms.internal.firebase_database.zzbt.zza(Unknown Source) at com.google.android.gms.internal.firebase_database.zzgx.zzdr(Unknown Source) at com.google.android.gms.internal.firebase_database.zzhd.run(Unknown Source) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Looks like the thing that you think is a String is actually a Map instead. — Doug Stevenson
Please add your database structure and please also responde with @. — Alex Mamo

Boris Ruzanov Boris Ruzanov · Accepted Answer · 2019-06-10T20:07:56

In this line

String value = dataSnapshot.getValue(String.class);

You are trying to extract value. Trying to make a string value on left side so on right side of = also suppose to be string. To make that in getValue you need to use your class pojo. And only AFTER that extract value. For example

User user = dataSnapshot.getValue(User.class);
String finalValue = user.getSomeString();

I am trying to get multiple nested data from firebase but getting this hashmap error

1 Answers