用户列表为空

Question

我正在尝试从 RealTime-Database 检索包含名字和姓氏的用户列表，但没有显示任何内容。

class UsersActivity 显示来自 database.I 的所有用户尝试了很多教程，但似乎没有任何效果。

public class UsersActivity extends AppCompatActivity {
    private RecyclerView userslist;
    private DatabaseReference ref;
    private List<Users> mUsers;

    @Override
    protected void onCreate (Bundle savedInstanceState) {
        super.onCreate ( savedInstanceState );
        setContentView ( R.layout.activity_users );
        ref = FirebaseDatabase.getInstance ().getReference ().child ( "FirstName" );

        userslist = (RecyclerView) findViewById ( R.id.users_list );

        userslist.setHasFixedSize ( true );
        userslist.setLayoutManager ( new LinearLayoutManager ( this ) );


    }
    public void readUsers(){
        FirebaseUser firebaseUser= FirebaseAuth.getInstance ().getCurrentUser ();
        DatabaseReference reference=FirebaseDatabase.getInstance ().getReference ("spors-budy-en866");
        reference.addValueEventListener ( new ValueEventListener () {
            @Override
            public void onDataChange (@NonNull DataSnapshot dataSnapshot) {

            }

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

            }
        } )
    }

    @Override
    protected void onStart () {
        super.onStart ();
        FirebaseRecyclerOptions<Users> options = new FirebaseRecyclerOptions.Builder<Users> ()
                .setQuery ( ref, Users.class )
                .build ();
        FirebaseRecyclerAdapter<Users, FindFriendViewHolder> adapter = new FirebaseRecyclerAdapter<Users, FindFriendViewHolder> ( options ) {
            @Override
            protected void onBindViewHolder (@NonNull FindFriendViewHolder findFriendViewHolder, int i, @NonNull Users users) {
                findFriendViewHolder.userName.setText ( users.getName () );

            }

            @NonNull
            @Override
            public FindFriendViewHolder onCreateViewHolder (@NonNull ViewGroup parent, int viewType) {
                View view = LayoutInflater.from ( parent.getContext () ).inflate ( R.layout.users_template, parent, false );
                FindFriendViewHolder viewHolder = new FindFriendViewHolder ( view );
                return viewHolder;
            }
        };
        userslist.setAdapter ( adapter );
        adapter.startListening ();
    }

    public static class FindFriendViewHolder extends RecyclerView.ViewHolder {
        TextView userName;
        ImageView profileImage;

        public FindFriendViewHolder (@NonNull View itemView) {
            super ( itemView );
            userName = itemView.findViewById ( R.id.username1 );
            profileImage = itemView.findViewById ( R.id.profilepicture );

        }


    }
}

我的数据库规则：

{
  "rules": {
    ".read": "true",
      ".write":"true",
    "users":{
    "$user_id":{
       ".read": "auth.uid === $user_id",
       ".write": "auth.uid === $user_id"

    }
  }
}
}

我希望向 databse.But 的所有用户显示 activity 是空的。

Answer 1

您正在设置：

ref = FirebaseDatabase.getInstance().getReference().child("FirstName");

然后使用它来初始化 FirebaseUI 适配器：

FirebaseRecyclerOptions<Users> options = new FirebaseRecyclerOptions.Builder<Users> ()
        .setQuery(ref, Users.class )

虽然我不知道您的数据模型，但您似乎不太可能在 /FirstName 下有一个用户列表，这是使用 FirebaseUI 适配器显示这些用户所需要的。

更有可能将 ref 初始化为：

ref = FirebaseDatabase.getInstance().getReference("users")

Answer 2

1-   ref=firebaseDatabase.getReference("FirstName");
2-   ref.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
  //**HERE WHERE YOU SHOULD FETCH THE DATA FROM YOUR DATABASE**



           String value=dataSnapshot.getValue(String.class);

            list.add(value);

            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                 list.clear();
                String value=dataSnapshot.getValue(String.class);

                list.add(value);
            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

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

            }
        });

最后你的数据库应该是这样的：希望对你有用

用户列表为空

Users list empty

android

firebase-realtime-database

firebaseui