Firebase - (DataSnapshot with multiple child nodes) - NullPointerException

Question

Goal: I am trying to pull data from Firebase and insert the values into Strings from nested nodes (in Android.)

Note: It's FINE for the first variable/key-value pair(mNum) but gets NullPointer for the others

Research: Firebase docs, Youtube, Stackoverflow about this specific question including: How to get child of child value from firebase in android?

How this applies to others: Trouble finding information on getting Firebase database information when DB has multiple nestings

Error:

java.lang.NullPointerException: println needs a message
                                                                                at android.util.Log.println_native(Native Method)
                                                                                at android.util.Log.i(Log.java:211)
                                                                                at com.netgalaxystudios.timeclock.RegisterSubscriptionActivity$1.onDataChange(RegisterSubscriptionActivity.java:80)

The error points to this line: Log.i("micro name", micro);

Database: Picture of Firebase DB that is being used

RegisterSubscriptionActivity.java:

public class RegisterSubscriptionActivity extends Activity {

    private DatabaseReference mDatabase;
    private DatabaseReference mDatabaseMicro;

    ArrayList subscriptionInfo;

    //Subscription (String) values
    String micro, small, medium, large, enterprise;
    String mNum, sNum, medNum, lNum, eNum;
    String mPrice, sPrice, medPrice, lPrice, ePrice;


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

        subscriptionInfo = new ArrayList<>();


        //GET INSTANCE OF FIREBASE DB & GRAB SUBSCRIPTION DATA
        mDatabase = FirebaseDatabase.getInstance().getReference("Subscription");
        mDatabaseMicro = mDatabase.child("Micro");
        mDatabaseMicro.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) { //literally a "snapshot" of the data
                //dataSnapshot.

                for(DataSnapshot subscriptionDataSnapshot : dataSnapshot.getChildren()) {

                    if (subscriptionDataSnapshot.getKey().equals("mNum")) {
                        mNum= subscriptionDataSnapshot.getValue().toString();
                    }
                    if(subscriptionDataSnapshot.getKey().equals("mPrice")) {
                        mPrice = subscriptionDataSnapshot.getValue().toString();
                    }
                    if(subscriptionDataSnapshot.getKey().equals("micro")) {
                        micro = subscriptionDataSnapshot.getValue().toString();
                    }

                    Log.i("micro number", mNum);
                    //Log.i("micro price", mPrice);
                    Log.i("micro name", micro);

                    String subscriptions = subscriptionDataSnapshot.getValue(String.class); //Each time it gets the key/value pair per node
                    subscriptionInfo.add(subscriptions);


                }

score 1 · Answer 1 · answered Dec 02 '17 at 06:54

To get the data under Micro node, please use the following code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference microRef = rootRef.child("Subscription").child("Micro");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String mNum = ds.child("mNum").getValue(String.class);
            String mPrice = ds.child("mPrice").getValue(String.class);
            String micro = ds.child("micro").getValue(String.class);
            Log.d("TAG", mNum + " / " + mPrice + " / " + micro);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
microRef.addListenerForSingleValueEvent(eventListener);

Your outout will be:

10 Employees / 25 / Micro

its working but if i have multiple subscription node and every node has a micro child node then how to get it? — Makvin, Nov 27 '18 at 11:43
@Makvin Your question is beyond the scope of this question. Please ask another question that explains the problem so me or other users can help you. — Alex Mamo, Nov 27 '18 at 11:46

score 0 · Accepted Answer · answered Nov 30 '17 at 19:22

0

Did you mean to put those log statements outside the for loop? The first time through loop it will match on "mNum" but micro will still be null.

answered Nov 30 '17 at 19:22

John O'Reilly

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Firebase - (DataSnapshot with multiple child nodes) - NullPointerException

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