CODEWITHSUNDEEP
javaandroidfirebasegoogle-cloud-firestorenullpointerexception
Nikhil Kathpalia
Nikhil Kathpalia

Reputation: 13

Attempt to invoke virtual method 'boolean com.google.firebase.firestore.DocumentSnapshot.exists()' on a null object reference

I am getting a null pointer reference while using firebase firestore and my app is crashing. Here's my code :

private FirebaseFirestore fstore=FirebaseFirestore.getInstance();

private DocumentReference documentReference=fstore.collection("users").document("17030121084");
@Override
    protected void onStart(){
        super.onStart();
        documentReference.addSnapshotListener(this, new EventListener<DocumentSnapshot>() {
            @Override
            public void onEvent(@Nullable DocumentSnapshot documentSnapshot, @Nullable FirebaseFirestoreException e) {

                if (documentSnapshot.exists()){
                    String semester=documentSnapshot.getString("sem");
                    sem.setText(semester);
                }
            }
        });
    }

The sem here refers to my field in my document 17030121084.

Can someone please suggest a solution for this?

Upvotes: 1

Views: 521

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 598728

If there was an error while trying to read the document, the documentSnapshot variable will be null. So your code needs to check for that.

The simplest way to do so is by adding a simple null check:

public void onEvent(@Nullable DocumentSnapshot documentSnapshot, @Nullable FirebaseFirestoreException e) {
    if (document != null && documentSnapshot.exists()){
        String semester=documentSnapshot.getString("sem");
        sem.setText(semester);
    }
}

But the above code is not handling the error yet. And since clearly document is null in your situation, you'll actually need to know what the error is in order to be able to fix it.

So this is a better approach:

public void onEvent(@Nullable DocumentSnapshot documentSnapshot, @Nullable FirebaseFirestoreException e) {
    if (e != null) {
        Log(TAG, "Listen failed.", e);
        return;
    }

    if (documentSnapshot.exists()){
        String semester=documentSnapshot.getString("sem");
        sem.setText(semester);
    }
}

Note that this code closely matches what's in the documentation on listening for documents, so I highly recommend spending some time there.

Upvotes: 1

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