java.lang.NullPointerException: Attempt to invoke virtual method to call the data from firebase

Question

I am trying to get the database collection from Firestore but getting two errors first warning is:

Do not place Android context classes in static fields

Second, when I call the database, it shows:

java.lang.NullPointerException: Attempt to invoke virtual method

I found so many similar questions, but it does not help me so I asked new question

public static List<BookModel> bookList = new ArrayList<>();
    public static FirebaseFirestore g_firestore;
    public static void  LoadBook(MyCompleteListener completeListener){
        bookList.clear();
        g_firestore.collection("BOOKS").get()
            .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                @Override
                public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                    Map<String, QueryDocumentSnapshot> docList = new ArrayMap<>();
                    for (QueryDocumentSnapshot doc: queryDocumentSnapshots ){
                        docList.put(doc.getId(),doc);

                    }
                    QueryDocumentSnapshot bookListDoc = docList.get("Categories");


                    assert bookListDoc != null;
                    Long bookCount = bookListDoc.getLong("COUNT");
                    for (int i=1; 1<= bookCount ;i++){
                        String bookID =  bookListDoc.getString("BOOK"+String.valueOf(i)+"_ID");
                        QueryDocumentSnapshot bookDoc = docList.get(bookID);
                        assert bookDoc != null;
                        int noOfBook = Objects.requireNonNull(bookDoc.getLong("NO_OF_BOOK")).intValue();
                        String bookName = bookDoc.getString("NAME");
                        String bookType = bookDoc.getString("TYPE");

                        bookList.add(new BookModel( bookID,bookName,bookType,noOfBook));

                    }
                    completeListener.onSuccess();

                }
            }).addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {

                }
            });
    }
}

java.lang.RuntimeException: Unable to start activity
java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.firestore.CollectionReference com.google.firebase.firestore.FirebaseFirestore.collection(java.lang.String)' on a null object reference` at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3782)

` java.lang.RuntimeException: Unable to start activity java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.firestore.CollectionReference com.google.firebase.firestore.FirebaseFirestore.collection(java.lang.String)' on a null object reference` at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3782) — Sarthak Tiwari
– Sarthak Tiwari, Commented Feb 25, 2024 at 11:01

Alex Mamo · Accepted Answer · 2024-02-25 11:47:28Z

0

You are getting the this error:

java.lang.RuntimeException: Unable to start activity java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.firestore.CollectionReference com.google.firebase.firestore.FirebaseFirestore.collection(java.lang.String)' on a null object reference

Because of the following line of code:

g_firestore.collection("BOOKS").get().addOnSuccessListener(/* ... /*)

This means that g_firestore is null. Why? Because you didn't initialize it in the first place. To solve this, please change this line:

public static FirebaseFirestore g_firestore;

To:

public static FirebaseFirestore g_firestore = FirebaseFirestore.getInstance();

answered Feb 25, 2024 at 11:47

Alex Mamo

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5 Comments

Sarthak Tiwari Over a year ago

but i getting this

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Long com.google.firebase.firestore.QueryDocumentSnapshot.getLong(java.lang.String)' on a null object reference

dan1st Over a year ago

Looks like docList.get("Categories") returns null - Why should it not do that?

Alex Mamo Over a year ago

@SarthakTiwari That seems to be another NPE. So the fact that you are getting another error, means that the initial error disappeared and this is good news :) but this sounds like a new issue which basically should be considered another question. So, please post a new question, here on StackOverflow, using its own MCVE, so I and other Firebase developers can help you.

Alex Mamo Over a year ago

Did my answer help? Can I help you with other information regarding the initial issue?

Sarthak Tiwari Over a year ago

yes it help but i am getting still issue that

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