继承FirebaseRecyclerAdapter时报DataSnapshot无法转换为Posts类怎么解决

我在进行Android开发时，需要为RecyclerView创建适配器，因此继承FirebaseRecyclerAdapter类实现逻辑，但运行时抛出异常。我在网上找到的同类示例均采用该继承方式，不确定是自身代码存在问题还是该继承方式已不再支持，恳请各位帮忙排查解决，非常感谢。

适配器代码 #

public class PostAdapterTest extends FirebaseRecyclerAdapter <Posts, PostAdapterTest.postsViewHolder> {
    private BottomSheetDialog bottomSheetDialog;
    private Context mContext;
    private Boolean downloadOrOpen = false;
    private boolean buttonStatus = true;
    private DatabaseReference likesRef = FirebaseDatabase.getInstance().getReference("Likes");
    private FirebaseUser mFirebaseUser = FirebaseAuth.getInstance().getCurrentUser();

    private String difficulty = null;

    private int likesCounter;
    private ReadWritePermissions mReadWritePermissions;

    public PostAdapterTest(@NonNull FirebaseRecyclerOptions<Posts> postsFirebaseRecyclerOptions,  ReadWritePermissions mReadWritePermissions, Context mContext)
    {
        super(postsFirebaseRecyclerOptions);
        this.mContext = mContext;
        this.mReadWritePermissions = mReadWritePermissions;
    }

    @Override
    protected void onBindViewHolder(@NonNull PostAdapterTest.postsViewHolder holder, int position, @NonNull Posts model) {
        final String postKey = getRef(position).getKey();
        String postUid = model.getPostId();

        holder.nickname.setText(model.getNickname());
        holder.country.setText(model.getCountry());
        holder.title.setText(model.getCountry());
        holder.days.setText(model.getDays());
        holder.kilometers.setText(model.getKilometers());
        holder.description.setText(model.getDescription());

        difficulty = model.getDifficulty();

        holder.map.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Uri mapUri = Uri.parse(model.getMap());
                mapOptions(mapUri);
            }
        });

        holder.comments.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                CommentsFragment commentsFragment = new CommentsFragment();
                Bundle args = new Bundle();
                args.putString("postId", postUid);

                commentsFragment.setArguments(args);

                FragmentTransaction fragmentTransaction = ((FragmentActivity)mContext).getSupportFragmentManager().beginTransaction();
                fragmentTransaction.replace(R.id.frame_container, commentsFragment);
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();

            }
        });

        holder.setLikeButtonStatus(postKey);

        holder.likes.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                buttonStatus = true;

                likesRef.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {
                        if(buttonStatus == true)
                        {
                            if(snapshot.child(postKey).hasChild(mFirebaseUser.getUid()))
                            {
                                likesRef.child(postKey).child(mFirebaseUser.getUid()).removeValue();
                                buttonStatus = false;
                            }else
                            {
                                likesRef.child(postKey).child(mFirebaseUser.getUid()).setValue(true);
                                buttonStatus = false;
                            }
                        }
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError error) {

                    }
                });

                switch (difficulty)
                {
                    case "Easy":
                        holder.difficulty.setImageResource(R.drawable.ic_easy);
                        break;

                    case "Difficult":
                        holder.difficulty.setImageResource(R.drawable.ic_difficult);
                        break;

                    case "Hard":
                        holder.difficulty.setImageResource(R.drawable.ic_hard);
                        break;
                }

                ArrayList<Slider> sliderArrayList = new ArrayList<>();

                Picasso.get().load(model.getAvatarUri()).into(holder.avatarUri);
            }
        });
    }

    @NonNull
    @Override
    public PostAdapterTest.postsViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.posts, parent, false);
        return new PostAdapterTest.postsViewHolder(view);
    }

    class postsViewHolder extends RecyclerView.ViewHolder
    {
        public CircleImageView avatarUri;
        public TextView nickname, country, title, days, likesNum, kilometers,description, fileSize, fileName;
        public SliderView mSliderView;
        public ImageView comments, save, difficulty;
        public ImageButton likes;
        public ImageButton more;
        public LinearLayout map;

        public postsViewHolder(@NonNull View itemView) {
            super(itemView);

            avatarUri = itemView.findViewById(R.id.posts_profile_picture);
            nickname = itemView.findViewById(R.id.posts_nickname);
            country = itemView.findViewById(R.id.posts_country);
            title = itemView.findViewById(R.id.posts_title);
            days = itemView.findViewById(R.id.posts_days);
            difficulty = itemView.findViewById(R.id.posts_difficulty);
            mSliderView = itemView.findViewById(R.id.posts_images);
            likes = itemView.findViewById(R.id.posts_likes);
            comments = itemView.findViewById(R.id.posts_comments);
            save = itemView.findViewById(R.id.posts_save);
            likesNum = itemView.findViewById(R.id.posts_likes_number);
            description = itemView.findViewById(R.id.posts_description);
            more = itemView.findViewById(R.id.posts_more);
            kilometers = itemView.findViewById(R.id.posts_distance);
            fileSize = itemView.findViewById(R.id.posts_uploaded_file_size);
            fileName = itemView.findViewById(R.id.posts_uploaded_file_name);
            map = itemView.findViewById(R.id.posts_map_layout);
        }

        public void setLikeButtonStatus(final String key)
        {
            mFirebaseUser = FirebaseAuth.getInstance().getCurrentUser();

            likesRef.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {
                    likesCounter = (int)snapshot.child(key).getChildrenCount();
                    if(snapshot.child(key).hasChild(mFirebaseUser.getUid()))
                    {
                        likes.setImageResource(R.drawable.ic_liked_red);
                        likesNum.setText(likesCounter + " Likes");
                    }else if(likesCounter == 0)
                    {
                        likes.setImageResource(R.drawable.ic_unliked_red);
                        likesNum.setText("");
                    }else
                    {
                        likes.setImageResource(R.drawable.ic_unliked_red);
                        likesNum.setText(likesCounter + " Likes");
                    }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError error) {

                }
            });
        }
    }

    private void mapOptions(Uri mapUri)
    {
       
    }
}

Logcat错误信息 #

Process: com.company.android.myapplication, PID: 8349
java.lang.ClassCastException: com.google.firebase.database.DataSnapshot cannot be cast to com.company.android.myapplication.Posts
    at com.company.android.myapplication.test.PostAdapterTest.onBindViewHolder(PostAdapterTest.java:44)
    at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:149)
    at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7254)
    at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7337)
    at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6194)
    at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6460)
    at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6300)
    at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6296)
    at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2330)
    at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
    at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
    at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4309)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4012)
    at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)

解决方案 #

该错误和FirebaseRecyclerAdapter的继承方式无关，核心原因是FirebaseUI无法将数据库返回的DataSnapshot转换成自定义的Posts类，按以下步骤排查即可：

1. 检查Posts类的结构：必须包含公共无参构造方法，所有需要映射的字段要么是公共属性，要么有对应的get/set方法，字段名要和数据库中的字段名完全一致，大小写也不能错，如果字段名不匹配需要添加@PropertyName注解显式指定对应的数据库字段名。
2. 检查FirebaseRecyclerOptions的初始化代码：确认你设置的Query指向的数据库节点下，每个子节点的结构都和Posts类完全匹配，不要误指向了包含其他数据结构的上层节点。
3. 定位具体转换问题：可以临时在构建Options时手动获取对应位置的DataSnapshot，调用snapshot.getValue(Posts.class)并添加try-catch，捕获转换异常后查看具体的字段不匹配提示，快速定位问题。

内容的提问来源于stack exchange，提问作者allim