android - 从微调器中选择项目时未显示 ListView

Question

我正在创建两个微调器:一个用于城市，另一个用于该特定城市的区域。根据用户在上述微调器中所做的选择，将显示一个 ListView，该 ListView 对于用户在微调器中所做的不同选择组合会有所不同。我正在从存储在 Firebase 中的数据库中获取 Listview 的数据。 Java 代码中提到的 URL 每次都会更改。但是 ListView 本身没有显示。

具有微调器和 ListView 的布局如下:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="100dp"
    >
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Select a City"
        />

    <Spinner
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/selectCity"
        android:entries="@array/city_name"
        android:textSize="20sp"
        android:singleLine="false"
        android:prompt="@string/city_title"
        android:outlineProvider="background"

        android:background="@android:drawable/btn_dropdown"
        />
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Select Area"
        android:paddingTop="20sp"
        />
    <Spinner
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/select_area"
        android:background="@android:drawable/btn_dropdown"
        >
    </Spinner>
    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"

        android:id="@+id/displayAllAstrologers"

        ></ListView>

</LinearLayout>

我用来处理微调器和 Listview 的 java fragment 代码是:

 package com.example.hsports.weddingplanner.Fragments;


    import android.content.Context;
    import android.content.Intent;
    import android.content.SharedPreferences;
    import android.os.Bundle;
    import android.support.annotation.Nullable;
    import android.support.v4.app.Fragment;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.AdapterView;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.Spinner;

    import com.example.hsports.weddingplanner.Activities.FrontPage;
    import com.example.hsports.weddingplanner.Adapters.displayingListCategories;
    import com.example.hsports.weddingplanner.R;
    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;

    /**
     * Created by I324671 on 12/5/2016.
     */
    public class Location_Selection extends Fragment {
        ArrayList<String> listCategories=new ArrayList<>();

        String categorySelected;

        String citySelected="";
        String areaSelected="";
        public  Location_Selection(String categorySelected)
        {
            this.categorySelected= this.categorySelected;
        }
        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            View view=inflater.inflate(R.layout.city_selection_page,container,false);
            final Spinner areaSelector=(Spinner)view.findViewById(R.id.select_area);
            Spinner selectCity=(Spinner)view.findViewById(R.id.selectCity);
            final ListView listView = (ListView) view.findViewById(R.id.displayAllAstrologers);
           selectCity.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
               @Override
               public void onItemSelected(AdapterView<?> parent, final View view, int position, long id) {

                   final ArrayList<String> listAreas = new ArrayList<String>();

                   String s = parent.getItemAtPosition(position).toString();
                   FirebaseDatabase database = FirebaseDatabase.getInstance();
                   DatabaseReference reference = database.getReference(s);

                   reference.addValueEventListener(new ValueEventListener() {
                       @Override
                       public void onDataChange(DataSnapshot dataSnapshot) {

                           if (dataSnapshot.hasChildren()) {
                               for (DataSnapshot child : dataSnapshot.getChildren()) {
                                   String areaId = child.getKey().toString();
                                   String areaName = child.getValue().toString();
                                   listAreas.add(areaName);
                               }
                           }
                           ArrayAdapter<String> adapter = new ArrayAdapter(view.getContext(),
                                   android.R.layout.simple_spinner_item, listAreas);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                           areaSelector.setAdapter(adapter);
                       }
                       @Override
                       public void onCancelled(DatabaseError databaseError) {
                       }
                   });

               }
               @Override
               public void onNothingSelected(AdapterView<?> parent) {

               }
           });
            areaSelector.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                @Override
                public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                    FirebaseDatabase database1 = FirebaseDatabase.getInstance();
                    DatabaseReference reference1 = database1.getReference("Astrologer-Hoodi/email");
                    reference1.addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {

                            if (dataSnapshot.hasChildren()) {
                                for (DataSnapshot child : dataSnapshot.getChildren()) {
                                    String getEmailNo = child.getKey().toString();
                                    String getEmailId = child.getValue().toString();
                                    listCategories.add(getEmailId);
                                }
                            }
listView.setAdapter(new displayingListCategories(getContext(), listCategories));
                        }
                        @Override
                        public void onCancelled(DatabaseError databaseError) {
                        }

                    });



                }

                @Override
                public void onNothingSelected(AdapterView<?> parent) {

                }
            });

            return  view;
        }
           }

我正在使用 baseAdapter 来扩充 xml 中的 ListView。所以扩展BaseAdapter的Adapter类如下:

package com.example.hsports.weddingplanner.Adapters;

import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.CursorAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.example.hsports.weddingplanner.R;
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;

/**
 * Created by I324671 on 12/5/2016.
 */
public class displayingListCategories extends BaseAdapter {

    private Context mcontext;

    public ArrayList<String> listCategories;

    public displayingListCategories(Context context,ArrayList<String> listCategories) {
        //super(context, c);
        mcontext=context;
        this.listCategories=listCategories;
    }


    @Override
    public int getCount() {
        return 0;
    }

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

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

        View view= LayoutInflater.from(convertView.getContext()).inflate(R.layout.format_of_list_of_categories, parent, false);
        ImageView imageView=(ImageView)view.findViewById(R.id.image_of_customer);
        imageView.setImageResource(R.drawable.customer_photo);
        TextView nameOfCustomer=(TextView)view.findViewById(R.id.name_of_customer);
        TextView emailIdOfCustomer=(TextView)view.findViewById(R.id.email_id_of_customer);
        TextView phoneOfCustomer=(TextView)view.findViewById(R.id.phone_no_of_customer);
        nameOfCustomer.setText(listCategories.get(position));
        emailIdOfCustomer.setText(listCategories.get(position));
        phoneOfCustomer.setText(listCategories.get(position));
            return view;
    }
}

我没有显示 ListView 。我希望 ListView 对于微调器中的不同选择是不同的。

Answer 1

您是否在 selectCity onItemSelectListener 上使用了 DatabaseReference addValueEventListener。在您不添加任何值之前，不会调用 onDataChange。所以没有被调用，你的适配器还没有准备好填充下一个列表。