尝试在空对象引用上调用虚拟方法“…………”

Question

i'm a newbie and i have a project for my thesis but i got some problems. so, i always get this error when i run my project, because of that my app always force close.

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

i don't know where's the problems, or maybe i write the wrong code. please help me! thankyou!

---

public static void loadHome(MyCompleteListener completeListener){

        g_homeList.clear();

        g_firestore.collection("kuis").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 homeListDoc = docList.get("jml_kuis");

                        long homeCount = homeListDoc.getLong("count");

                        for( int i=1; i <= homeCount; i++){

                            String docID = homeListDoc.getString("kuis" + String.valueOf(i) + "_id");
                            QueryDocumentSnapshot homeDoc = docList.get(docID);

                            int numOfTest = homeDoc.getLong("no_kuis").intValue();
                            String homeName = homeDoc.getString("name");
                            g_homeList.add(new HomeViewModel(docID, homeName, numOfTest));

                        }

                        completeListener.OnSuccess();

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

                        completeListener.OnFailure();

                    }
                });


    }

Answer 1

Looks like some of your doc Ids are null. To fix this you might to check the data coming from firebase for the missing id.

To make the code run have add null checks like this:

 for(QueryDocumentSnapshot doc : queryDocumentSnapshots){
   if(doc.getId()!==null){
     docList.put(doc.getId(), doc);
   }
}
                    }