java - 从 Firebase 检索数据到 fragment 上嵌入的 RecyclerView

Question

我试图在嵌入 fragment 的 RecyclerView 上显示此列表的名称(以蓝色突出显示):

我想像这样给他们看我一开始就试过这个:

public void onStart() {
        super.onStart();
        Query query= FriendRef.child(Current_User);
        FirebaseRecyclerOptions<get_setDataUser> options= new FirebaseRecyclerOptions.Builder<get_setDataUser>()
                .setQuery(query, get_setDataUser.class)
                .build();
            FirebaseRecyclerAdapter adapter =
                    new FirebaseRecyclerAdapter<get_setDataUser, FriendViewHolder>(options) {
                @NonNull
                @Override
                public FriendViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.user_single_layout,parent,false);
                    FriendViewHolder holder = new FriendViewHolder(view);
                    return holder;}
                @Override
                protected void onBindViewHolder(@NonNull final FriendViewHolder friendViewHolder, int position, @NonNull get_setDataUser get_setDataUser) {
                    String users = getRef(position).getKey();
                    UserRef.child(users).addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                            String name = dataSnapshot.child("name").getValue().toString();
                            String status = dataSnapshot.child("status").getValue().toString();
                            friendViewHolder.username.setText(name);
                            friendViewHolder.userStatus.setText(status);

                        }

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

                        }
                    });

                }
            };
            FriendList.setAdapter(adapter);
            adapter.startListening();

    }

它给了我那个错误:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.firebaseauthentication, PID: 15545
    com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.firebaseauthentication.get_setDataUser
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(com.google.firebase:firebase-database@@16.0.4:423)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@16.0.4:214)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(com.google.firebase:firebase-database@@16.0.4:79)
        at com.google.firebase.database.DataSnapshot.getValue(com.google.firebase:firebase-database@@16.0.4:212)
        at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:29)
        at com.firebase.ui.database.ClassSnapshotParser.parseSnapshot(ClassSnapshotParser.java:15)
        at com.firebase.ui.common.BaseCachingSnapshotParser.parseSnapshot(BaseCachingSnapshotParser.java:35)
        at com.firebase.ui.common.BaseObservableSnapshotArray.get(BaseObservableSnapshotArray.java:52)
        at com.firebase.ui.database.FirebaseRecyclerAdapter.getItem(FirebaseRecyclerAdapter.java:106)
        at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:122)
        at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7065)
        at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7107)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2303)
        at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1627)
        at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
        at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
        at androidx.recyclerview.widget.RecyclerView.consumePendingUpdateOperations(RecyclerView.java:1897)
        at androidx.recyclerview.widget.RecyclerView$1.run(RecyclerView.java:414)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
        at android.view.Choreographer.doCallbacks(Choreographer.java:686)
        at android.view.Choreographer.doFrame(Choreographer.java:618)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

所以我尝试在 Arraylist 中获取 UserIDs 列表，然后将其显示在 RecyclerView 上，但它无法正常工作，那么我该如何让它工作:

public void onStart() { 
        super.onStart();
        Query query= FriendRef;
        FirebaseRecyclerOptions options= new FirebaseRecyclerOptions.Builder<get_setDataUser>()
                .setQuery(query, get_setDataUser.class)
                .build();
            FirebaseRecyclerAdapter adapter = 
                    new FirebaseRecyclerAdapter<get_setDataUser, FriendViewHolder>(options) {
                @NonNull
                @Override
                public FriendViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.user_single_layout,parent,false);
                    FriendViewHolder holder = new FriendViewHolder(view);
                    return holder;}
                @Override
                protected void onBindViewHolder(@NonNull final FriendViewHolder friendViewHolder, int position, @NonNull get_setDataUser get_setDataUser) {

                    Users = new ArrayList<String>();
                    FriendRef.child(Current_User).addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                            for(DataSnapshot ds:dataSnapshot.getChildren()){ 
                                Users.add(ds.getKey()); }
                        }
                        @Override
                        public void onCancelled(@NonNull DatabaseError databaseError) {
                            Log.w("DataSnapshot","Not reading data");
                        }
                    });
                    for (int i= 0 ; i<Users.size();i++){
                       String Frind= Users.get(i);
                    UserRef.child(Frind).addValueEventListener(new ValueEventListener() {
                         @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                            String name = dataSnapshot.child("name").getValue().toString();
                            String status = dataSnapshot.child("status").getValue().toString();
                            friendViewHolder.username.setText(name);
                            friendViewHolder.userStatus.setText(status);
                        }
                        @Override
                        public void onCancelled(@NonNull DatabaseError databaseError) {

                        }
                    });
                  }
                }
            };
            FriendList.setAdapter(adapter);
            adapter.startListening();

    }

FriendViewHolder:

public static class FriendViewHolder extends RecyclerView.ViewHolder{
            TextView username,userStatus;
        public FriendViewHolder(@NonNull View itemView) {
            super(itemView);
            username=itemView.findViewById(R.id.user_single_name);
            userStatus=itemView.findViewById(R.id.user_single_status);

        }
    } 

OnCreat:

public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        FriendsFragView = inflater.inflate(R.layout.fragment_friends, container, false);
        FriendList = FriendsFragView.findViewById(R.id.FriendList);
        FriendList.setHasFixedSize(true);
        FriendList.setLayoutManager(new LinearLayoutManager(getContext()));

        auth = FirebaseAuth.getInstance();
        Current_User= auth.getCurrentUser().getUid();

        UserRef = FirebaseDatabase.getInstance().getReference().child("Users");
        FriendRef = FirebaseDatabase.getInstance().getReference().child("Friends");

        UserRef.keepSynced(true);
        FriendRef.keepSynced(true);
        return FriendsFragView;
    }

get_setDataUser 类:

public class get_setDataUser {
    String name;
    String status;

    public get_setDataUser() {
    }

    public get_setDataUser(String name, String status) {
        this.name = name;
        this.status = status;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public String getName() {
        return name;
    }

    public String getStatus() {
        return status;
    }
}

Answer 1

无法将 String 类型的对象转换为 get_setDataUser 类型。你 friend 的 child 是一个字符串。你用蓝线表示。您必须像这样更改您的选项和适配器:

 FirebaseRecyclerOptions<String> options= new FirebaseRecyclerOptions.Builder<String>()
            .setQuery(query, String.class)
            .build();
        FirebaseRecyclerAdapter adapter =
                new FirebaseRecyclerAdapter<String, FriendViewHolder>(options) {
            @NonNull
            @Override
            public FriendViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
                View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.user_single_layout,parent,false);
                FriendViewHolder holder = new FriendViewHolder(view);
                return holder;}
            @Override
            protected void onBindViewHolder(@NonNull final FriendViewHolder friendViewHolder, int position, @NonNull String userid) {
                UserRef.child(userid).addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                      // if you want you can convert dataSnapshot to get_setDataUser here
                      // get_setDataUser user = dataSnapshot.getValue(get_setDataUser.class);
                      //  friendViewHolder.username.setText(user.getName());
                      //   friendViewHolder.userStatus.setText(user.getStatus());
                        String name = dataSnapshot.child("name").getValue().toString();
                        String status = dataSnapshot.child("status").getValue().toString();
                        friendViewHolder.username.setText(name);
                        friendViewHolder.userStatus.setText(status);

                    }

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

                    }
                });

            }
        };
        FriendList.setAdapter(adapter);