java.lang.NullPointerException：

Question

执行我的应用程序时，我收到以下错误：

java.lang.NullPointerException：无法为 child() 中的参数“pathString”传递 null

但我之前没有收到这个错误。有人可以帮助我吗？

请看错误控制台，以及上面的java代码

消息片段.java

MessagesFragment 中的第一个错误，错误发生在 MessagesDbRef 中，但 firebase 不为空。

public class MessagesFragment extends Fragment {

    private static final String TAG = MessagesFragment.class.getSimpleName();

    private FirebaseAuth mAuth;

    private FirebaseUser user;

    private DatabaseReference userDbRef;

    private DatabaseReference messagesDbRef;

    private DatabaseReference conversationsDbRef;

    private FirebaseRecyclerAdapter firebaseRecyclerAdapter;

    private RecyclerView recyclerViewConversations;

    private Context context;

    ImageView imgViewNoMessages;

    TextView txtNoMessages;

    private String currentUserId;

    public MessagesFragment() {

    }

    @Override

    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        View messagesView = inflater.inflate(R.layout.fragment_messages, container, false);

        imgViewNoMessages = (ImageView) messagesView.findViewById(R.id.image_no_messages);

        txtNoMessages = (TextView) messagesView.findViewById(R.id.text_no_messages);

        this.context = getContext();

        mAuth = FirebaseAuth.getInstance();

        user = mAuth.getCurrentUser();

        if (user != null) {

            currentUserId = user.getUid();

        }

        recyclerViewConversations = (RecyclerView) messagesView.findViewById(R.id.rv_conversations);

        userDbRef = FirebaseDatabase.getInstance().getReference().child("Users");

        userDbRef.keepSynced(true);

        conversationsDbRef = FirebaseDatabase.getInstance().getReference().child("Chat").child(currentUserId);

        conversationsDbRef.keepSynced( true );

        messagesDbRef = FirebaseDatabase.getInstance().getReference().child("Messages").child(currentUserId);

        messagesDbRef.keepSynced(true);

    }

Answer 1

您似乎没有共享类的所有代码。所以我只有猜测；if (user != null) {   currentUserId = user.getUid(); }这些行表示如果用户为空，则 currentUserId 将为空。    conversationsDbRef = FirebaseDatabase.getInstance().getReference().child("Chat").child(currentUserId);在这一行看来，传递的参数currentUserId为 null 并且该 null 是 NullPointerException 的原因