java - 未调用 addValueEventListener

Question

我正在尝试使用 Firebase 获取存储在我的数据库中的数据，但未调用 addValueEventListener。下面是我的数据库的样子:

下面是我的规则:

下面是我的代码:

package com.example.user.equichange;

 import android.app.ProgressDialog;
 import android.content.ClipData;
 import android.content.Context;
 import android.net.Uri;
 import android.os.Bundle;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.design.widget.FloatingActionButton;
 import android.support.design.widget.TabLayout;
 import android.support.v4.app.Fragment;
 import android.support.v4.view.ViewPager;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.Toolbar;
 import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.ImageView;
 import android.widget.TextView;

 import com.firebase.client.Firebase;
 import com.firebase.client.FirebaseError;
 import com.firebase.ui.database.FirebaseRecyclerAdapter;
 import com.google.firebase.database.DataSnapshot;
 import com.google.firebase.database.DatabaseError;
 import com.google.firebase.database.DatabaseReference;
 import com.google.firebase.database.FirebaseDatabase;
 import com.google.firebase.database.ValueEventListener;
 import com.google.firebase.storage.StreamDownloadTask;

 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;





public class NoAddOns_Tab_fragment extends Fragment {
RecyclerView recyclerView;
Adapter adapter;
List<ITEM> list;
String TAG = "TAG";

Firebase firebasedb;
DatabaseReference mdatabaseref;

public NoAddOns_Tab_fragment() {

}


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


    return view;
}

@Override
public void onViewCreated( View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);


    recyclerView = (RecyclerView)view.findViewById(R.id.recyclerView_no_Top_ups);
    mdatabaseref = FirebaseDatabase.getInstance().getReference().child("Users");
    Log.d(TAG, "onViewCreated: "+mdatabaseref.getRoot());

    mdatabaseref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Log.d(TAG, "onDataChange: " + dataSnapshot);
            Log.d(TAG,dataSnapshot.getChildren().toString());

            list = new ArrayList<ITEM>();

                for (DataSnapshot dataSnapshot1:dataSnapshot.getChildren()){
                    Log.d(TAG, "onDataChange: In the loop " + dataSnapshot1.toString());


                    ITEM value = dataSnapshot1.getValue(ITEM.class);
                    ITEM itemModel = new ITEM();

                    String Title = value.getTitle();
                    Log.d(TAG, "onDataChange:Title "+ value.getTitle());



                    String Description = value.getDescription();
                    String Amount = value.getAmount();

                    itemModel.setTitle(Title);
                    itemModel.setDescription(Description);
                    itemModel.setAmount(Amount);

                    list.add(itemModel);
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.d(TAG, "onCancelled: Error");

        }
    });

//        Log.d(TAG, "LIST "+ list);


    Adapter adapter = new Adapter(getContext(),list);
    recyclerView.setLayoutManager(new GridLayoutManager(getContext(),2));
    recyclerView.setAdapter(adapter);
}

我的 firebase 已正确设置，因为我可以将数据发送到 Firebase 数据库:

从我的 logcat 你可以看到 Log.d(TAG, "onDataChange: In the loop "+ dataSnapshot1.toString());没有被调用。即使是 log.d(TAG,"On data cange"+ datasnapshot) 也没有被调用，这意味着有问题..有人可以帮我吗

Answer 1

获取值时无需遍历任何内容。 ValueEventListener 会为您完成这项工作。因此，摆脱 for 循环并仅使用 ITEM value = dataSnapshot.getValue(ITEM.class); 应该适合您。快速提问，您是否使用 ITEM 类将数据存储在 Firebase 中？如果是这样，这个解决方案应该有效。否则，您需要使用与设置数据相同的类来从 Firebase 检索数据。