java - Android应用程序在空对象引用上退出 'boolean com.google.firebase.firestore.DocumentSnapshot.exists()'问题

我的应用程序有问题，我真的需要您的帮助。我是Android Studio的新手，我不知道为什么我的应用程序在SignOut上崩溃。我认为是由于Query SnapShot和以下代码行:

我只会说一点英语，所以我为我的英语不好而深感抱歉:)

这是我的HomeFragment的代码

 Query firstQuery =
 firebaseFirestore.collection("Posts").orderBy("timestamp",
 Query.Direction.DESCENDING).limit(3);
         firstQuery.addSnapshotListener(getActivity(), new EventListener<QuerySnapshot>() {
             @Override
             public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
                 if (!documentSnapshots.isEmpty()) {
                     if (isFirstPageFirstLoad) {
                         lastVisible = documentSnapshots.getDocuments().get(documentSnapshots.size() - 1);
                         blog_list.clear();
                     }

                     for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {

                         if (doc.getType() == DocumentChange.Type.ADDED) {

                             String blogPostId = doc.getDocument().getId();
                             BlogPost blogPost = doc.getDocument().toObject(BlogPost.class).withId(blogPostId);

                             if (isFirstPageFirstLoad) {
                                 blog_list.add(blogPost);
                             } else {
                                 blog_list.add(0, blogPost);
                             }
                             blogRecyclerAdapter.notifyDataSetChanged();
                         }
                     }
                     isFirstPageFirstLoad = false;
                 }
             }
         });
     }
     // Inflate the layout for this fragment
     return view;
 }

 public void loadMorePost(){
     if(firebaseAuth.getCurrentUser() != null) {
         final Query nextQuery = firebaseFirestore.collection("Posts")
                 .orderBy("timestamp", Query.Direction.DESCENDING)
                 .startAfter(lastVisible)
                 .limit(3);

         nextQuery.addSnapshotListener(getActivity(), new EventListener<QuerySnapshot>() {
             @Override
             public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
                 if (!documentSnapshots.isEmpty()) {
                     lastVisible = documentSnapshots.getDocuments().get(documentSnapshots.size() - 1);
                     for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {
                         if (doc.getType() == DocumentChange.Type.ADDED) {
                             String blogPostId = doc.getDocument().getId();
                             BlogPost blogPost = doc.getDocument().toObject(BlogPost.class).withId(blogPostId);
                             blog_list.add(blogPost);
                             blogRecyclerAdapter.notifyDataSetChanged();
                         }
                     }
                 }
             }
         });

对于MainActivity，我只能使用它:

private void logOut() {
    mAuth.signOut();
    sendToLogin();
}

BlogRecyclerAdapter.java

    firebaseFirestore.collection("Posts/" + blogPostId + "/Likes").addSnapshotListener( new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
            if(!documentSnapshots.isEmpty()){
                int count = documentSnapshots.size();
                holder.updateLikesCount(count);

            } else {
                holder.updateLikesCount(0);
            }
        }
    });

和我的致命错误:在BlogRecyclerAdapter上，但是如果我删除BlogRecyclerAdapter上的所有代码，我的应用程序仍然崩溃!我认为真正的问题在于HomeFragment!

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: learnorburn.lob_application, PID: 15909
                  java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.google.firebase.firestore.QuerySnapshot.isEmpty()' on a null object reference
                      at learnorburn.lob_application.BlogRecyclerAdapter$2.onEvent(BlogRecyclerAdapter.java:117)
                      at learnorburn.lob_application.BlogRecyclerAdapter$2.onEvent(BlogRecyclerAdapter.java:113)
                      at com.google.firebase.firestore.zzi.onEvent(Unknown Source)
                      at com.google.android.gms.internal.zzevc.zza(Unknown Source)
                      at com.google.android.gms.internal.zzevd.run(Unknown Source)
                      at android.os.Handler.handleCallback(Handler.java:751)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6776)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1510)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1400)

预先感谢您的帮助

最佳答案

您的查询或数据库设置中有错误。检查EventListener的文档。它说:



因此，在您的情况下，如果QuerySnapshot documentSnapshots是null，则意味着FirebaseFirestoreException e不是null。但是，您会吞下此异常。相反，您应该将其记录下来并检查那里写的内容:

Log.e("MyTag", "Firebase exception", e);

关于java - Android应用程序在空对象引用上退出 'boolean com.google.firebase.firestore.DocumentSnapshot.exists()'问题，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/52097674/