Question

我遇到了以下问题。当我试图从FirebaseRecyclerAdapter获取值时，我得到null，只键入我能看到的这个。请查看我的代码：

 public abstract class TabFragmentLists extends Fragment {

    private DatabaseReference mDatabase;

    private FirebaseRecyclerAdapter<Post, PostViewHolder> mAdapter;
    private RecyclerView mRecycler;
    private LinearLayoutManager mManager;

    public TabFragmentLists() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView (LayoutInflater inflater, ViewGroup container,
                              Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);
        View rootView = inflater.inflate(R.layout.fragment_tab_lists, container, false);

        mDatabase = FirebaseDatabase.getInstance().getReference();
        mRecycler = (RecyclerView) rootView.findViewById(R.id.messages_list);
        mRecycler.setHasFixedSize(true);

        return rootView;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        // Set up Layout Manager, reverse layout
        mManager = new LinearLayoutManager(getActivity());
        mManager.setReverseLayout(true);
        //mManager.setStackFromEnd(true);

        mRecycler.setLayoutManager(mManager);

        // Set up FirebaseRecyclerAdapter with the Query
        Query postsQuery = getQuery(mDatabase);
        mAdapter = new FirebaseRecyclerAdapter<Post, PostViewHolder>(Post.class, R.layout.item_post,
                PostViewHolder.class, postsQuery) {
            @Override
            protected void populateViewHolder(final PostViewHolder viewHolder, final Post model, final int position) {
                final DatabaseReference postRef = getRef(position);

                // Set click listener for the whole post view
                final String postKey = postRef.getKey();

                viewHolder.bindToPost(model, new View.OnClickListener() {
                    @Override
                    public void onClick(View postView) {
                        Log.e("OnClick","== Bind===");
                    }
                });
            }
        };

        mRecycler.setAdapter(mAdapter);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (mAdapter != null) {
            mAdapter.cleanup();
        }
    }

    public String getUid() {
        return FirebaseAuth.getInstance().getCurrentUser().getUid();
    }

    public abstract Query getQuery(DatabaseReference databaseReference);
}

PostViewHolder

public class PostViewHolder extends RecyclerView.ViewHolder {

    public TextView messsageView;
    public PostViewHolder(View itemView) {
        super(itemView);

        messsageView = (TextView) itemView.findViewById(R.id.post_message);
    }

    public void bindToPost(Post post, View.OnClickListener starClickListener) {
        //null and crash
        Log.e("Post", String.valueOf(post.getMessage())); 
        messsageView.setText(post.getMessage());
    }
}

发布课程

@IgnoreExtraProperties
public class Post {

    public String message;
    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }


    public Post() {
        // Default constructor required for calls to DataSnapshot.getValue(Post.class)
    }

    public Post(String message) {
        this.message = message;
    }

    @Exclude
    public Map<String, Object> toMap() {
        HashMap<String, Object> result = new HashMap<>();
        result.put(PostKeys.kMessage.toString(), message);
        return result;
    }

}

这是DB结构

会欣赏任何提示。感谢

修改

public class TabFragmentPosts extends TabFragmentLists {

    public TabFragmentPosts() {
        // Required empty public constructor
    }

    @Override
    public Query getQuery(DatabaseReference databaseReference) {
        // All my posts
        return databaseReference.child("post");
    }

}

这正是我最终拥有的

E/LIST dataSnapshot: DataSnapshot { key = -KOgO2hC9Fh_vhe1kh1z, value = null }

Answer 1

最后，发现了问题 class Post应该具有相同的变量名称（考虑大写/小写）

@IgnoreExtraProperties

public class Post {

    public String Message; // HERE IS THE PROBLEM WAS

    public Post() {
        // Default constructor required for calls to DataSnapshot.getValue(Post.class)
    }

    public Post(String Message) {
        this.Message = Message;
    }

    @Exclude
    public Map<String, Object> toMap() {
        HashMap<String, Object> result = new HashMap<>();
        result.put("Message", Message);
        return result;
    }
}

感谢所有试图帮助的人！欣赏它！

Answer 2

首先检查安全规则，无论您是否已启用权限...如果未启用权限...在以下链接中查找如何设置权限... https://firebase.google.com/docs/database/security/quickstart

Answer 3

除非我误读了您的代码，否则您似乎错误地设置了您的DatabaseReference - 您目前只是将其指向基础Firebase参考，但您需要将其指向您的＆＃39 ;交＆＃39;路径。

您需要在mDatabase属性中添加.child（＆＃34; post＆＃34;）。

FirebaseRecyclerAdapter获取null值

3 个答案: