Android fragments Firebase+；RecyclerView:RecyclerView在应用程序启动时不显示

我正在使用Android Studio提供的类进行选项卡式活动，该活动使用带有ViewPager的操作栏选项卡。在这个活动中，我试图用Firebase数据库中的数据初始化RecyclerView

问题：在应用程序第一次运行时，RecyclerView为空，如下所示

如果我在emulator中关闭并重新打开应用程序，我的RecyclerView将按其应该的方式填充，如下所示

你知道为什么会这样吗？我有一个理论，但还没有找到解决办法。在尝试阅读该页面后，我得到的印象是，这些片段必须是静态的（我不知道这可能意味着什么，因此，如果有人能对此有所了解，我将不胜感激）。在应用程序第一次运行时，它会初始化RecyclerView。然后添加Firebase数据库中的数据，但由于RecyclerView已经初始化，因此它是空的，并且从未正确更新。我试着打电话通知。。。方法无效

StudentFragment的onCreateView方法：

private View view;
private Context c;
private RecyclerView mRecyclerView;
private LinearLayoutManager manager;
private Firebase mFirebaseRef;
private FirebaseRecyclerAdapter<Student, ViewHolder> firebaseRecyclerAdapter;


public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.fragment_students, container, false);
    mFirebaseRef = new Firebase("<your Firebase link here>");
    c = getContext();

    //Initializes Recycler View and Layout Manager.
    mRecyclerView = (RecyclerView) view.findViewById(R.id.studentRecyclerView);
    manager = new LinearLayoutManager(c);
    mRecyclerView.setHasFixedSize(true);
    firebaseRecyclerAdapter =
            new FirebaseRecyclerAdapter<Student, ViewHolder>(
                    Student.class,
                    R.layout.single_student_recycler,
                    ViewHolder.class,
                    mFirebaseRef
            ) {
                @Override
                protected void populateViewHolder(ViewHolder viewHolder, Student student, int i) {
                    viewHolder.vFirst.setText(student.getFirst());
                    viewHolder.vLast.setText(student.getLast());
                    viewHolder.vDue.setText(Double.toString(student.getCurrentlyDue()));
                    viewHolder.vRadio.setButtonTintList(ColorStateList.valueOf(Color.parseColor(student.getColor())));
                    Log.d(TAG, "populateViewHolder called");
                }
            };

    mRecyclerView.setAdapter(firebaseRecyclerAdapter);
    mRecyclerView.setLayoutManager(manager);


    return view;
}

主屏幕的onCreate方法：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_homescreen);

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.container);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(mViewPager);

}

Firebase上下文设置在另一个应用程序上，该应用程序在主屏幕活动启动后立即启动。任何帮助都将不胜感激

---

编辑：我在FirebaseUI GitHub页面中搜索，这是最有可能出现问题的地方，发现另一个用户也有同样的问题。似乎在FirebaseRecyclerAdapter类中插入NotifyItem之后没有调用onBindViewHolder。现在要解决它…

让我试试，就像你在问题标题上说的那样

RecyclerView在应用程序启动时不显示

那么

初始化回收器视图和布局管理器

应在onStart上声明

@Override
   public void onStart() {
       super.onStart();
       mFirebaseRef = new Firebase("<your Firebase link here>");
       firebaseRecyclerAdapter = ...
       //and so on

@覆盖
public void onStart（）{
super.onStart（）；
mFirebaseRef=新Firebase（“”）；
firebaseRecyclerAdapter=。。。
//等等

希望有帮助

 firebaseRecyclerAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
        @Override
        public void onItemRangeInserted(int positionStart, int itemCount) {
            super.onItemRangeInserted(positionStart, itemCount);
            int friendlyMessageCount = firebaseRecyclerAdapter.getItemCount();
            int lastVisiblePosition =
                    linearLayoutManager.findLastCompletelyVisibleItemPosition();
            // If the recycler view is initially being loaded or the
            // user is at the bottom of the list, scroll to the bottom
            // of the list to show the newly added message.
            if (lastVisiblePosition == -1 ||
                    (positionStart >= (friendlyMessageCount - 1) &&
                            lastVisiblePosition == (positionStart - 1))) {
                linearLayoutManager.scrollToPosition(positionStart);
            }
        }
    });
    recyclerListIdeas.setAdapter(firebaseRecyclerAdapter);

---

**只需添加Recyclerview.AdapterDataObserver（）。对我有用！希望它有帮助：）**

我也有同样的问题，请查看文档：

通过添加数据观察者修复了此问题：

mFirebaseAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
   @Override
   public void onItemRangeInserted(int positionStart, int itemCount) {
   super.onItemRangeInserted(positionStart, itemCount);
   int friendlyMessageCount = mFirebaseAdapter.getItemCount();
   int lastVisiblePosition =
          mLinearLayoutManager.findLastCompletelyVisibleItemPosition();
   // If the recycler view is initially being loaded or the 
   // user is at the bottom of the list, scroll to the bottom 
   // of the list to show the newly added message.
   if (lastVisiblePosition == -1 ||
           (positionStart >= (friendlyMessageCount - 1) &&
                   lastVisiblePosition == (positionStart - 1))) {
       mMessageRecyclerView.scrollToPosition(positionStart);
      }
   }
});

---

在我的例子中，这是由

mRecyclerView.setHasFixedSize（true）引起的

如果您注释掉这行代码，列表将正确加载。我从这次讨论中得到了解决方案：

我正试图做与您相同的事情，但无法实现，以下是我的问题的解释，以防您有时间查看。谢谢！谢谢！这也是我的问题！太好了，我的问题也是如此。

mFirebaseAdapter.registerAdapterDataObserver(new RecyclerView.AdapterDataObserver() {
   @Override
   public void onItemRangeInserted(int positionStart, int itemCount) {
   super.onItemRangeInserted(positionStart, itemCount);
   int friendlyMessageCount = mFirebaseAdapter.getItemCount();
   int lastVisiblePosition =
          mLinearLayoutManager.findLastCompletelyVisibleItemPosition();
   // If the recycler view is initially being loaded or the 
   // user is at the bottom of the list, scroll to the bottom 
   // of the list to show the newly added message.
   if (lastVisiblePosition == -1 ||
           (positionStart >= (friendlyMessageCount - 1) &&
                   lastVisiblePosition == (positionStart - 1))) {
       mMessageRecyclerView.scrollToPosition(positionStart);
      }
   }
});