回收者视图未在Android Studio中显示一张卡片视图

我试图通过回收者视图在片段的卡视图中显示阵列列表。阵列列表包含要在片段的五个卡视图上显示的五个值。但是它只显示四个.fragment的代码如下所示：

public class AddMemberFragment extends Fragment {

private RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;
private RecyclerView.LayoutManager mLayoutManager;
private View view ;
FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference mRootRef = FirebaseDatabase.getInstance().getReference();
String userId;
String n_team ;
private ArrayList<Friend> friends;


public AddMemberFragment() {
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.addnewfriend_fragment, container, false);
    return view;
}

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

    userId = firebaseUser.getUid();
    ManageTeamTabbedActivity activity = (ManageTeamTabbedActivity) getActivity();
    n_team = activity.getMyData();
    mRecyclerView = (RecyclerView) getView().findViewById(R.id.addNewFriend);
    mLayoutManager = new LinearLayoutManager(getActivity());
    mRecyclerView.setLayoutManager(mLayoutManager);


    mRootRef.child("users").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            ArrayList<Friend> friendArrayList = new ArrayList<>();
            for (DataSnapshot userSnapshot : dataSnapshot.getChildren()) {
                Log.d("demo", "USERID " + FirebaseAuth.getInstance().getCurrentUser().getUid());
                Friend friend = new Friend();
                friend.setId(userSnapshot.getKey());
                friend.setFriendName((String) userSnapshot.child("profiles").child("fname").getValue());  //Implement it
                friendArrayList.add(friend);
            }
            friends = friendArrayList;
            mAdapter = new AddFriendAdapter(getActivity(), friends, n_team);
            mRecyclerView.setAdapter(mAdapter);


        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

适配器代码如下所示。

public class AddFriendAdapter extends RecyclerView.Adapter<AddFriendAdapter.RecyclerViewHolder>{

private ArrayList<Friend> mData;
private Context mContext;
private FirebaseAuth auth;
private String u_team ;

public AddFriendAdapter(Context mContext, ArrayList<Friend> friendList , String u_team) {
    this.mData = friendList;
    this.mContext = mContext;
    this.u_team= u_team;
}

@Override
public RecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.addnewfriend_layout, parent, false);
    AddFriendAdapter.RecyclerViewHolder viewHolder = new AddFriendAdapter.RecyclerViewHolder(view);
    return viewHolder;
}

@Override
public void onBindViewHolder(RecyclerViewHolder holder, final int position) {
    final Friend frnd =(Friend) mData.get(position);

    holder.friendName.setText(frnd.getFriendName());
    holder.addFriend.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            frnd.setStatus("sent");
            final DatabaseReference mRootRef = FirebaseDatabase.getInstance().getReference();
            final FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
            final String UID = firebaseUser.getUid();
            mRootRef.child("users").addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    mRootRef.child("users").child(UID).child("Your Teams").child("requests").child(frnd.getId()).setValue(frnd);
                    Friend temp = new Friend();
                    temp.setId(firebaseUser.getUid());
                    temp.setFriendName(firebaseUser.getDisplayName());
                    temp.setStatus("received");
                    mRootRef.child("users").child(frnd.getId()).child("Your Teams ").child("requests").child(firebaseUser.getUid()).setValue(temp);
                    mData.remove(frnd);
                    notifyDataSetChanged();
                }

                @Override

                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }
    });
}

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

public class RecyclerViewHolder extends RecyclerView.ViewHolder {
    TextView friendName;
    ImageButton addFriend;

    public RecyclerViewHolder(View itemView) {
        super(itemView);
        friendName = (TextView)itemView.findViewById(R.id.textViewFriendName);
        addFriend = (ImageButton) itemView.findViewById(R.id.imagebuttonFriendAdd);
    }
}

模拟器的屏幕截图也已随附，其中“添加新成员”片段中有四个卡视图。

我很累自己调试它，发现数组列表中的条目与预期的一样是五个。

还附带了数据库图片供参考。如图所示，它也有五个ID要显示，但“回收者”视图显示四个ID。