ListView显示空字段而不是Firebase中的数据

Question

我有一个ListView，我想用它从Firebase检索数据（2个textviews：沙拉名称和沙拉价格每一行）。不幸的是，行总是空的。数据似乎是核心进行 - 行数总是与沙拉节点中的项目数相同。

这是我的activity_adapter_listing.xml文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:background="@android:color/holo_blue_dark"
>

<TextView
    android:id="@+id/saladName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textSize="30sp"
    android:layout_alignParentLeft="true"
    android:textColor="@android:color/white"
   />

<TextView
    android:id="@+id/saladPrice"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textSize="30sp"
    android:layout_alignParentRight="true"
    android:textColor="@android:color/white"

    />

activity_menu.xml文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">


<ListView
    android:id="@+id/allsalads"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:visibility="visible"
    android:layout_marginBottom="50dp"
    >
</ListView>

ListingAdapter.java：

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
import java.util.ArrayList;
public class ListingAdapter extends BaseAdapter {
Context context;
LayoutInflater layoutInflater;
ArrayList<Salad> salad;
public ListingAdapter(Context con, ArrayList<Salad> salad)
{
    context=con;
    layoutInflater = LayoutInflater.from(context);
    this.salad=salad;
}
// return number of salads in firebase
@Override
public int getCount() {
    return salad.size();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        convertView = layoutInflater.inflate(R.layout.activity_adapter_listing, null, false);
        holder = new ViewHolder();
        holder.name = (TextView) convertView.findViewById(R.id.saladName);
        holder.price = (TextView) convertView.findViewById(R.id.saladPrice);
        convertView.setTag(holder);

    } else {
        holder = (ViewHolder) convertView.getTag();
    }
    Salad salads=salad.get(position);
    holder.name.setText(salads.getName());
    holder.price.setText(salads.getPrice());
    return convertView;
}
public class ViewHolder {
    TextView name, price;
}
@Override
public Object getItem(int position) {
    return salad.get(position);
}
@Override
public long getItemId(int position) {
    return position;
}
}

我的MenuActivity.java：

import android.app.ProgressDialog;
import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
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;

public class MenuActivity extends AppCompatActivity { 
ListView allsalads;
ProgressDialog mProgressDialog;
DatabaseReference databaseReference= FirebaseDatabase.getInstance().getReference();
ListingAdapter adapter;
ArrayList<Salad> salads=new ArrayList<>();
Button saladBtn, pizzaBtn, drinkBtn;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_menu);
    allsalads=(ListView)findViewById(R.id.allsalads);
    adapter=new ListingAdapter(MenuActivity.this,salads);
    allsalads.setAdapter(adapter);
    getDataFromServer(); 
}


public void getDataFromServer()
{
    showProgressDialog();
    databaseReference.child("Sałatki").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if(dataSnapshot.exists())
            {
                for(DataSnapshot postSnapShot:dataSnapshot.getChildren())
                {
                    Salad salad=postSnapShot.getValue(Salad.class);
                    salads.add(salad);
                    adapter.notifyDataSetChanged();
                }
            }
            hideProgressDialog();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            hideProgressDialog();
        }
    });
}
private void showProgressDialog() {
    if (mProgressDialog == null) {
        mProgressDialog = new ProgressDialog(MenuActivity.this);
        mProgressDialog.setMessage("Loading...");
        mProgressDialog.setIndeterminate(true);
    }

    mProgressDialog.show();
}

private void hideProgressDialog() {
    if (mProgressDialog != null && mProgressDialog.isShowing()) {
        mProgressDialog.dismiss();
    }
}


private class ListingAdapter extends BaseAdapter {

    Context context;
    LayoutInflater layoutInflater;
    ArrayList<Salad> salads;

    public ListingAdapter(Context con,ArrayList<Salad> salads)
    {
        context=con;
        layoutInflater = LayoutInflater.from(context);
        this.salads=salads;
    }

    @Override
    public int getCount() {
        return salads.size();
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;

        if (convertView == null) {
            convertView = layoutInflater.inflate(R.layout.activity_adapter_listing, null, false);
            holder = new ViewHolder();

            holder.name = (TextView) convertView.findViewById(R.id.saladName);
            holder.price = (TextView) convertView.findViewById(R.id.saladPrice);
            convertView.setTag(holder);

        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        Salad salad=salads.get(position);

        holder.name.setText(salad.getName());
        holder.price.setText(salad.getPrice());

        return convertView;
    }

    public class ViewHolder {
        TextView name, price;

    }
    @Override
    public Object getItem(int position) {
        return salads.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }
}}

和Salad.java：

public class Salad {
private String name, price;

Salad(){
}

public String getName() {
    return name;
}

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

public String getPrice() {
    return price;
}

public void setPrice(String price) {
    this.price = price;
}}

我不知道我在哪里弄错了。

This is how it looks when i run the APK