如何从 Firebase 数据库中填充 ListView 中的多个 TextView？

Question

我首先构建了一个 ListView，它包含多个 没有 Firebase 的 TextView，并且运行良好（注意：我将数据存储在字符串数组中）。然后我用一个 TextView with Firebase 创建了一个 ListView (ArrayAdapter)，效果也很好（注意：我将数据存储在一个 ArrayList 中）。但是一旦我将这两个项目合并在一起，它就不起作用了（注意：这个项目中存在多个 TextView，但我现在只是试图填充我的第一个 TextView）。我的应用会在尝试打开时立即关闭。

更新：在我使用 Firebase 创建一个带有单个 TextView 的 ListView (ArrayAdapter) 的单独项目中，我改用了 .notifyDataSetChanged()。当我在该项目中使用 .notify() 时，它不再起作用。我在这个项目中使用 .notify() 是否会导致问题？我似乎无法在这个项目中使用 .notfiyDataSetChanged。

这是我的包含 ListView 的 activity_main：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="match_parent"
    tools:context=".MainActivity">

    <ListView
        android:id="@+id/eventsListView"
        android:layout_width="0dp"
        android:layout_height="100dp"
        android:layout_marginStart="32dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="32dp"
        android:divider="@android:color/darker_gray"
        android:dividerHeight="1dp"
        android:scrollbars="vertical"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

这是我的 activity_list_view，它概述了 ListView 的视图：

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

    <LinearLayout android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:id="@+id/eventTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:gravity="center_vertical"
            android:paddingTop="5dp"
            android:textSize="18sp"
            android:textStyle="bold" />

        <TextView
            android:id="@+id/eventDetails"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center_vertical"
            android:paddingBottom="5dp"
            android:textSize="16sp"
            android:textStyle="italic" />

        <TextView
            android:id="@+id/eventDescription"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:gravity="center_vertical"
            android:paddingBottom="5dp"
            android:textSize="16sp" />

    </LinearLayout>

</LinearLayout>

这是我的 MainActivity：

package com.example.firebase_listview_2;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ListAdapter;
import android.widget.ListView;
import com.google.firebase.database.ChildEventListener;
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 java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    ListView eventsList;
    DatabaseReference dawnEvents;
    ArrayList<String> titleArray = new ArrayList<>();
    ArrayList<String> eventStartArray = new ArrayList<>();
    ArrayList<String> eventFinishArray = new ArrayList<>();
    ArrayList<String> eventGenderArray = new ArrayList<>();
    ArrayList<String> eventAgeArray = new ArrayList<>();
    ArrayList<String> descriptionArray = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final ListAdapter adapter = new com.example.firebase_listview_2.ListAdapter(this, titleArray, eventStartArray, eventFinishArray, eventGenderArray, eventAgeArray, descriptionArray);
        eventsList = findViewById(R.id.eventsListView);
        eventsList.setAdapter(adapter);

        dawnEvents = FirebaseDatabase.getInstance().getReference("Timetable/Ladybridge High School, Bolton, UK/Date/2019-11-30/Events/Spanish Lesson");
        dawnEvents.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                String value = dataSnapshot.getValue(String.class);
                titleArray.add(value);
                adapter.notify(); // In the separate project where I created a ListView (ArrayAdapter) with a single TextView with Firebase, I used .notifyDataSetChanged() instead. When I use .notify() in that project, it no longer works. Is my use of .notify() in this project causing the issue? I cannot seem to use .notfiyDataSetChanged in this project.
            }

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

            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            }

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

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }
}

这是我的 ListAdapter：

package com.example.firebase_listview_2;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import java.util.ArrayList;

public class ListAdapter extends ArrayAdapter<String> {

    private final Activity context;
    private final ArrayList<String> titleArray;
    private final ArrayList<String> eventStartArray;
    private final ArrayList<String> eventFinishArray;
    private final ArrayList<String> eventGenderArray;
    private final ArrayList<String> eventAgeArray;
    private final ArrayList<String> descriptionArray;

    public ListAdapter(Activity context, ArrayList<String> titleArray, ArrayList<String> eventStartArray, ArrayList<String> eventFinishArray, ArrayList<String> eventGenderArray, ArrayList<String> eventAgeArray, ArrayList<String> descriptionArray) {
        super(context, R.layout.activity_list_view, titleArray);

        this.context = context;
        this.titleArray = titleArray;
        this.eventStartArray = eventStartArray;
        this.eventFinishArray = eventFinishArray;
        this.eventGenderArray = eventGenderArray;
        this.eventAgeArray = eventAgeArray;
        this.descriptionArray = descriptionArray;
    }

    public View getView(int position, View view, ViewGroup parent) {
        LayoutInflater inflater = context.getLayoutInflater();
        View rowView = inflater.inflate(R.layout.activity_list_view, null, true);

        TextView eventTitle = rowView.findViewById(R.id.eventTitle);
        TextView eventDetails = rowView.findViewById(R.id.eventDetails);
        TextView eventDescription = rowView.findViewById(R.id.eventDescription);

        eventTitle.setText(titleArray.get(position));
        String eventDetailsConcat = eventStartArray.get(position) + "-" + eventFinishArray.get(position) + ", " + eventGenderArray.get(position) + ", " + eventAgeArray.get(position);
        eventDetails.setText(eventDetailsConcat);
        eventDescription.setText(descriptionArray.get(position));

        return rowView;
    }
}

这是我的 Firebase 数据库结构的相关示例：

Timetable
   Ladybridge High School, Bolton, UK
      Date
         2019-11-30
            Spanish Lesson
               Age: "All ages"
               Description: "Example description for Spanish lesson"
               Finish: "18:00"
               Gender: "Male and female"
               Start: "16:00"
               Title: "Spanish for Beginners"

Answer 1

在您的 Firebase 事件侦听器中，您只是在 titleArray 中添加值。应用程序很可能会在这一行抛出 NullPointerException：

 String eventDetailsConcat = eventStartArray.get(position) + "-" + eventFinishArray.get(position) + ", " + eventGenderArray.get(position) + ", " + eventAgeArray.get(position);

来自 ListAdapter。

Answer 2

Blackbelts 在此问题中的回答解决了错误： Error: Cannot Resolve notifyDataSetChanged(); Android

总结一下： "notifyDataSetChanged 不是 ListAdapter 的方法，而是 BaseAdapter 的方法，（ArrayAdapter 是 BaseAdapter 的子类）"

代码更改自：

adapter.notify();

代码更改为：

((BaseAdapter)adapter).notifyDataSetChanged();