addListenerForSingleValueEvent未执行

Question

addListenerForSingleValueEvent根本没有执行。在运行调试器时，它不从数据库中获取数据。我甚至尝试过addValueEventListener，但没有用。

我已经添加了片段代码，我试图在其中执行此操作。

package com.example.visan.peds;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

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


public class Landing_mother extends Fragment {

    private List<Ailment> ailments;

    private RecyclerView recyclerView;
    LinearLayoutManager layoutManager;
    private RecyclerView.Adapter adapter;

    public Landing_mother(){}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

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

        ailments=new ArrayList<>();

        recyclerView =(RecyclerView)view.findViewById(R.id.recyclerView1);
        recyclerView.setHasFixedSize(true);

        layoutManager=new LinearLayoutManager(getActivity());
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);

        getData();

        adapter=new LandingAdapter(ailments,getActivity());

        recyclerView.setAdapter(adapter);
        return view;
    }

    private void getData(){
        FirebaseDatabase db=FirebaseDatabase.getInstance();
        DatabaseReference ref=db.getReference().child("Mother");

        if(ref!=null){
            ref.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    if (dataSnapshot.exists()){
                        Ailment ailment=new Ailment();
                        for (int i=0;i<dataSnapshot.getChildrenCount();i++){
                            String img=dataSnapshot.child(Integer.toString(i)).child("img").getValue(String.class);
                            ailment.setImage_url(img);
                            String name=dataSnapshot.child(Integer.toString(i)).child("name").getValue(String.class);
                            ailment.setName(name);
                            ailments.add(ailment);
                        }
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }else {
            Toast.makeText(getActivity(),"Reference not obtained",Toast.LENGTH_SHORT).show();
        }
    }
}

Answer 1

请注意，onDataChange不是主流程的一部分。您调用getData（）并假设立即从数据库中检索值，然后设置适配器。但实际上，onDataChange可能会在稍后解雇。尝试在onDataChange方法中使用setadapter或notifydatasethaschanged。