Question

我尝试将Firestore与ListView联系起来。使用我的Query，其中有20条记录和3条随机内容，放入ArrayList（randomPlaceList），然后我合理地尝试将此ArrayList包含到我的自定义{{} 1}}。但我想念一些......

用一些变化变量编辑;现在我有这个错误：

处理：com.example.arara.myapplication，PID：10283 java.lang.IndexOutOfBoundsException：索引：4，大小：0 at java.util.ArrayList.get（ArrayList.java:437） at com.example.arara.myapplication.MainActivity $ 1.onComplete（MainActivity.java:46）

在这一行：

adapter

ListViewPlaces类：

Peoples item = randomPlaceList.get(randomIndex);

适配器类：

public class MainActivity extends AppCompatActivity {

FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference placeRef = rootRef.collection("peoples");

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    placeRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(Task<QuerySnapshot> task) {
            if (task.isSuccessful()) {
                List<Peoples> peoplesList = new ArrayList<>();
                for (DocumentSnapshot document : task.getResult()) {
                    Peoples peoples = document.toObject(Peoples.class);
                    System.out.println(peoples);
                    peoplesList.add(peoples);
                }
                if (peoplesList.size() > 0) {
                    System.out.println(peoplesList);
                    int placeCount = peoplesList.size();
                    Random randomGenerator = new Random();
                    List<Peoples> randomPlaceList = new ArrayList<>();
                    for (int i = 0; i < 3; i++) {
                        int randomIndex = randomGenerator.nextInt(placeCount);;
                        Peoples item = randomPlaceList.get(randomIndex);
                        randomPlaceList.add(item);
                    }
                    ListView mListView = findViewById(R.id.place_list);
                    PeoplesAdapter peoplesAdapter = new PeoplesAdapter(getBaseContext(), randomPlaceList);
                    mListView.setAdapter(peoplesAdapter);
                }
            }
        }
    });
}

}

和Model类：

public class PeoplesAdapter extends ArrayAdapter<Peoples> {
public PeoplesAdapter(Context context, List<Peoples> list) {
    super(context, 0, list);
}

@NonNull
@Override
public View getView(int position, View listItemView, @NonNull ViewGroup parent) {
    if (listItemView == null) {
        listItemView = LayoutInflater.from(getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
    }
    Peoples peoples = getItem(position);
    Log.d("TAG", peoples.getName());
    String name = peoples.getName();
    ((TextView) listItemView).setText(name);

    return listItemView;
}
}

Firestore数据库：

Answer 1

这是使用Android自定义ListView将数据从Cloud Firestore数据库显示到ArrayAdapter的方法。

首先，要将数据添加到数据库，您应该使用以下代码行：

FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference placesRef = rootRef.collection("places");
Places places = new Places("PlaceOne", "ImageOne");
placesRef.document().set(places);

通过这种方式，您可以根据需要添加任意数量的地点。因此，您将拥有一个如下所示的数据库结构：

Firestore-root
   |
   --- places (collection)
         |
         --- placeIdOne (document)
         |      |
         |      --- image: "ImageOne"
         |      |
         |      --- name: "NameOne"
         |
         --- placeIdTwo (document)
         |      |
         |      --- image: "ImageTwo"
         |      |
         |      --- name: "NameTwo"
         |
         --- //And so on

要成为更多的作者，请看下面的图片：

如果要查询数据，则需要使用Query对象。

Query query = placesRef.whereEqualTo("name", "NameOne");

但是因为我在数据库中只有几条记录，所以我只使用placesRef CollectionReference。

假设您的.XML文件中已有ListView，如下所示：

<ListView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/place_list"/>

要显示数据，首先需要创建适配器类。这个类应该是这样的：

public class PlacesAdapter extends ArrayAdapter<Places> {
    public PlacesAdapter(Context context, List<Places> list) {
        super(context, 0, list);
    }

    @NonNull
    @Override
    public View getView(int position, View listItemView, @NonNull ViewGroup parent) {
        if (listItemView == null) {
            listItemView = LayoutInflater.from(getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
        }

        Places places = getItem(position);

        String name = places.getName();
        ((TextView) listItemView).setText(name);

        return listItemView;
    }
}

然后在onCreate()方法中使用以下代码：

placesRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            List<Places> placesList = new ArrayList<>();
            for (DocumentSnapshot document : task.getResult()) {
                Places places = document.toObject(Places.class);
                placesList.add(places);
            }

            int placeCount = placesList.size();
            Random randomGenerator = new Random();
            List<Places> randomPlaceList = new ArrayList<>();
            for (int i = 1; i <= 3; i++) {
                randomPlaceList.add(placesList.get(randomGenerator.nextInt(placeCount)));
            }
            ListView mListView = (ListView) findViewById(R.id.place_list);
            PlacesAdapter placesAdapter = new PlacesAdapter(getApplicationContext(), randomPlaceList);
            mListView.setAdapter(placesAdapter);
        }
    }
});

每次启动应用时，ListView中的结果将是3个随机位置。

什么错过，连接Firestore和ListView随机导致样本？

1 个答案: