无法从Firebase检索数据到列表视图

Question

I am unable to retrieve real time data from firebase, i followed many sites but nothing solves my problem. They were mostly on recycler view, But i want to retrieve my data onto a list view.. Ders no error but my list view is blank when i am running it in emulator. Moreover i cannot use firebase ui because it creates some problems in card view dependency used in my project.. Please help--

package com.serverphone.healthyfoods;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CheckedTextView;
import android.widget.ListView;

import com.firebase.client.ChildEventListener;
import com.firebase.client.DataSnapshot;
import com.firebase.client.Firebase;
import com.firebase.client.FirebaseError;

import java.util.ArrayList;

public class AlaCarte extends AppCompatActivity {

    ListView lv;
    String arr[]=new String[]{"Paneer Butter Masala","Chicken Butter Masala","Chicken Biriyani"};
    ArrayList al=new ArrayList();
    ArrayList food=new ArrayList();
    Button btn;


    Firebase mref;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_ala_carte);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("Alacarte!!");

        mref=new Firebase("https://healthy-foods-270de.firebaseio.com/Food items");

        lv=(ListView)findViewById(R.id.listView);
        btn=(Button)findViewById(R.id.button8);
        final ArrayAdapter<String> aa=new ArrayAdapter<String>(AlaCarte.this,android.R.layout.simple_list_item_multiple_choice,food);
        lv.setAdapter(aa);
        mref.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {

                //String key=dataSnapshot.getKey();
                //String value=dataSnapshot.getValue(String.class);
                //String item=key+"-->"+value;
                String value=dataSnapshot.getValue(String.class);
                food.add(value);
                aa.notifyDataSetChanged();

            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String s) {

            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

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

            }

            @Override
            public void onCancelled(FirebaseError firebaseError) {

            }
        });

        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                CheckedTextView checkedTextView = ((CheckedTextView) view);
                //checkedTextView.setChecked(!checkedTextView.isChecked());
                if (checkedTextView.isChecked()) {
                    checkedTextView.setChecked(false);
                    al.remove(adapterView.getItemAtPosition(i));
                } else {
                    checkedTextView.setChecked(true);
                    al.add(adapterView.getItemAtPosition(i));
                }

            }
        });
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                if (al.isEmpty()) {
                    Snackbar.make(view, "Select check boxes to place your order", Snackbar.LENGTH_LONG)
                            .setAction("Action", null).show();
                } else {
                    Intent i = new Intent(AlaCarte.this, ConfirmAlacarte.class);
                    i.putExtra("mylist",al);
                    startActivity(i);

                }
            }
        });

        /*FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });*/
    }

}

Answer 1

I've been there. I did not go through your whole code, but if you get the data from firebase and add it to your list, you need something like "refresh".

What i've done was;

I added a button on the bottom of my page and when i clicked it restart the intent.

Pseudo will be like ;

public void Refresh(View view){          //refresh is onClick name given to the button

    onRestart();
}


@Override
protected void onRestart() {

    // TODO Auto-generated method stub
    super.onRestart();
    Intent i = new Intent("YourClass".this, "YourClass".class);  //your class
    startActivity(i);
    finish();

}

This solved my issue, where i got the data but did not display in my listView.

You could also test it with ToastMessage if your "food" array is null or not.