只有滚动时才会加载带有Firebase数据的Recycler视图

Question

我正在使用Firebase并使用android.support.v7.widget.RecyclerView。问题是onStart视图加载为空，数据仅在滚动后填充。知道为什么吗？

代码：

RecyclerView （我正在设置一个空的适配器onStart以避免“RecyclerView：没有连接适配器;跳过布局”）：

 mLayoutManager = new LinearLayoutManager(getActivity());
 mLayoutManager.setReverseLayout(true);
 mLayoutManager.setStackFromEnd(true);
 mRecyclerView.setLayoutManager(mLayoutManager);
 mRecyclerView.setHasFixedSize(true);

 mRecyclerView.getRecycledViewPool().setMaxRecycledViews(1,0);                                     
 mRecyclerView.setAdapter(new RecyclerView.Adapter() {
        @Override
        public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            return null;
        }

        @Override
        public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {

        }

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

Firebase数据提取：

databaseReference.child("/News").orderByChild("createdAt").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(final DataSnapshot dataSnapshot) {

        for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {

            final News news = postSnapshot.getValue(News.class);
            final PostListClass postListClass = new PostListClass();
            //add fac id admin
            if (news.getFaculteId().equals(userFaculteId) || news.getFaculteId().equals("Admin")) {
                postListClass.setPostId(postSnapshot.getKey());
                postListClass.setPostTitle(news.getHeadlines());
                postListClass.setPostDescription(news.getDetails());

                databaseReference.child("/users").child(news.getAuthor()).addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot usersSnapShot) {
                        User user = usersSnapShot.getValue(User.class);

                        postListClass.setPostOwnerId(usersSnapShot.getKey());
                        postListClass.setPostOwnerName(user.getPrenom() + " " + user.getNom());
                        postListClass.setPostOwnerPromo(user.getPromotion());

                        try {
                            Calendar cal = Calendar.getInstance(Locale.ENGLISH);
                            cal.setTimeInMillis(news.getCreatedAt() * 1000);
                            SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy");
                            Date date = sdf.parse(DateFormat.format("dd-MM-yyyy", cal).toString());
                            String day = (String) android.text.format.DateFormat.format("dd", date);
                            String month = (String) android.text.format.DateFormat.format("MMM", date);
                            postListClass.setPostDate(day + " " + month);
                        } catch (java.text.ParseException e) {
                            e.printStackTrace();
                        }
                        storageRef.child("users/" + news.getAuthor() + ".jpg").getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
                            @Override
                            public void onSuccess(Uri uri) {
                                postListClass.setPostOwnerImageUrl(String.valueOf(uri));
                            }
                        }).addOnFailureListener(new OnFailureListener() {
                            @Override
                            public void onFailure(@NonNull Exception exception) {
                                // Handle any errors

                                if (exception.getClass().isInstance(StorageException.class)) {
                                    postListClass.setPostOwnerImageUrl("NullImage");

                                }

                            }
                        });

                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {
                    }
                });

                databaseReference.child("/News").child(postSnapshot.getKey()).child("/Comments").addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        postListClass.setPostComments(String.valueOf(dataSnapshot.getChildrenCount()));

                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });

                storageRef.child("News/" + postSnapshot.getKey() + ".png").getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
                    @Override
                    public void onSuccess(Uri uri) {
                        postListClass.setPostImageUrl(String.valueOf(uri));

                    }
                }).addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception exception) {

                        postListClass.setPostImageUrl("NullImage");

                    }
                });

                postListClasses.add(postListClass);


            }

        }

       postsAdapter = new PostsAdapter(getContext(), postListClasses);
        mRecyclerView.setAdapter(postsAdapter);

    }


    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

所以这是应用启动时的结果（三个字段缺少数据）：

滚动后（缺少数据填写）：

Answer 1

数据是从Firebase异步加载的。因此，当您将适配器附加到列表时，还没有数据。

一旦数据从服务器进入，您需要提醒其列表。您可以致电adapter.notifyDataSetChanged()。