Recycler View 不显示数据

Question

Recycler 视图不读取或显示来自 firebase 数据库的数据，这两天我想我想请你帮忙。 问题肯定不在 Firebase 数据库中，因为数据写入成功，但输出有问题。在我看来，问题出在 onStart，或者更确切地说是在将适配器连接到 Recycler 视图中

    public class HomeActivity extends RootActivity {
      FirebaseAuth mAuth;
      private FloatingActionButton fab;
      private MaterialCardView PostCard;
      private MaterialToolbar topAppBar;
      private NavigationView nav_view;
      private LottieAnimationView serach;
      private TextView userName, userLogin;
      private RecyclerView PostRV;
      private DrawerLayout drawerLayout;
      Context context;
      PostAdapter adapter;
      private ImageView userPick;
      DatabaseReference db;
      FirebaseDatabase firebaseDatabase;
      FirebaseStorage fs;
      StorageReference sr;
      FirebaseUser currentUser;
      List<Post> postList;


      @Override
      protected void onStart() {
          super.onStart();
          db.addValueEventListener(new ValueEventListener() {
              @Override
              public void onDataChange(@NonNull @NotNull DataSnapshot snapshot) {
                  postList = new ArrayList<>();
                  for (DataSnapshot postsnap : snapshot.getChildren()) {
                      Post post = postsnap.getValue(Post.class);
                      postList.add(post);
                  }

                  adapter = new PostAdapter(context, postList);
                  PostRV.setAdapter(adapter);
              }


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

              }
          });
      }
      

      @Override
      protected void onCreate(@Nullable Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_home);


          PostRV = (RecyclerView)

                  findViewById(R.id.PostRV);

          nav_view = (NavigationView)

                  findViewById(R.id.nav_view);

          drawerLayout = (DrawerLayout)

                  findViewById(R.id.drawerLayout);

          fab = (FloatingActionButton)

                  findViewById(R.id.fab);

          topAppBar = (MaterialToolbar)

                  findViewById(R.id.topAppBar);


          PostRV.setLayoutManager(new

                  LinearLayoutManager(HomeActivity.this));
          firebaseDatabase = FirebaseDatabase.getInstance();
          db = firebaseDatabase.getReference("Posts");







          topAppBar.setNavigationOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  drawerLayout.openDrawer(GravityCompat.START);
              }
          });


          mAuth = FirebaseAuth.getInstance();
          currentUser = mAuth.getCurrentUser();


          FirebaseStorage fr = FirebaseStorage.getInstance();


          mAuth = FirebaseAuth.getInstance();
          currentUser = mAuth.getCurrentUser();
          View hl = nav_view.getHeaderView(0);
          TextView userName = hl.findViewById(R.id.userName);
          TextView userLogin = hl.findViewById(R.id.userLogin);
          ImageView userPick = hl.findViewById(R.id.userPick);


          fab.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  Intent intent = new Intent(HomeActivity.this, AddActivity.class);
                  startActivity(intent);
              }
          });
      }
  }

后适配器

public  class  PostAdapter extends RecyclerView.Adapter<PostAdapter.MyViewHolder>{


Context mContext;
List<Post> mData;
public PostAdapter(Context mContext, List<Post> mData) {
    this.mContext = mContext;
    this.mData = mData;
}

@NonNull
@NotNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull @NotNull ViewGroup parent, int viewType) {
    View row = LayoutInflater.from(mContext).inflate(R.layout.row_signle_post,parent,false);

    return new MyViewHolder(row);
}

@Override
public void onBindViewHolder(@NonNull @NotNull MyViewHolder holder, int position) {
    holder.tvTitle.setText(mData.get(position).getTitle());
    holder.tvTitle.setText(mData.get(position).getUsername());
    Glide.with(mContext).load(mData.get(position).getUserPick()).into(holder.imgUserPick);
    Glide.with(mContext).load(mData.get(position).getPostImage()).into(holder.imgPost);

; }

@Override
public int getItemCount() {
    return 0;
}


public class MyViewHolder extends RecyclerView.ViewHolder {

    TextView tvTitle;
    TextView tvName;
    ImageView imgPost;
    TextView tag;
    CircleImageView imgUserPick;


    public MyViewHolder(@NonNull @NotNull View itemView) {
        super(itemView);


        tvTitle = itemView.findViewById(R.id.title);
        tvName = itemView.findViewById(R.id.username);
        tag = itemView.findViewById(R.id.tag);
        imgPost = itemView.findViewById(R.id.imgPost);
        imgUserPick = itemView.findViewById(R.id.userPick);





    }
}

后模型

ublic class Post {
private String title;
private String username;
private String postImage;
private String tag;
private String userId;
private String userPick;
private String description;
private String location;
private String wallet;
private Object time_stamp;


private String postKey;



public Post(String title, String username, String postImage, String tag, String userId, String userPick, String description, String location, String wallet) {
    this.username = username;
    this.title = title;
    this.tag = tag;
    this.userId = userId;
    this.userPick = userPick;
    this.description = description;
    this.wallet = wallet;
    this.postImage = postImage;
    this.location = location;
    this.time_stamp = DocumentTransform.FieldTransform.ServerValue.REQUEST_TIME;



}

public Post() {
}


public String getPostKey() {
    return postKey;
}

public void setPostKey(String postKey) {
    this.postKey = postKey;
}

public String getTitle() {
    return title;
}

public String getUsername() {
    return username;
}

public String getPostImage() {
    return postImage;
}

public String getTag() {
    return tag;
}

public String getUserId() {
    return userId;
}

public String getUserPick() {
    return userPick;
}



public String getDescription() {
    return description;
}

public String getLocation() {
    return location;
}

public String getWallet() {
    return wallet;
}


public Object getTime_stamp() {
    return time_stamp;
}

public void setTitle(String title) {
    this.title = title;
}

public void setUsername(String username) {
    this.username = username;
}

public void setPostImage(String postImage) {
    this.postImage = postImage;
}

public void setTag(String tag) {
    this.tag = tag;
}

public void setUserId(String userId) {
    this.userId = userId;
}

public void setUserPick(String userPick) {
    this.userPick = userPick;
}

public void setDescription(String description) {
    this.description = description;
}

public void setLocation(String location) {
    this.location = location;
}

public void setWallet(String wallet) {
    this.wallet = wallet;
}

public void setTime_stamp(Object time_stamp) {
    this.time_stamp = time_stamp;
}

}

Answer 1

adapter = new PostAdapter(context, postList);
              PostRV.setAdapter(adapter);
//check size of postList using log.i

//在recyclerview适配器中设置项目计数为mData.size()

@Override
public int getItemCount() {
    return mData.Size();
}