什么错过了，连接 Firestore 和 ListView 以获得样本中的随机结果? [英] What miss, with connect Firestore and ListView for random results in sample?

问题描述

我尝试将我的 Firestore 连接到 ListView.我的 Query 有 20 条记录和 3 条随机记录，放入 ArrayList(randomPlaceList)，然后我合乎逻辑地尝试包含这个 ArrayList 到我的自定义 adapter.但我想念一些东西..

I try to connect my Firestore to ListView. With my Query there are put 20 records and 3 random of it, put in ArrayList(randomPlaceList), then I logical try to include this ArrayList to my custom adapter. But I miss something..

编辑了一些变化变量；现在我有这个错误:

EDITED with some change variables; Now I have this error:

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

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

在这一行:

Peoples item = randomPlaceList.get(randomIndex);

ListViewPlaces 类:

ListViewPlaces class:

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);
                }
            }
        }
    });
}

}

适配器类:

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;
}
}

和模型类:

class Peoples {
private String name, age;

public Peoples() {}

public Peoples(String name, String age) {
    this.name = name;
    this.age = age;
}

public String getName() {
    return name;
}

public String getAge() {
    return age;
}
}

Firestore 数据库:

Firestore database:

推荐答案

这是将 Cloud Firestore 中的数据显示到ListView"中的方法使用自定义的ArrayAdapter"在 Android 上.

This is how you can display data from a Cloud Firestore into a "ListView" using a custom "ArrayAdapter" on Android.

首先，要向数据库中添加数据，您应该使用以下几行代码:

First of all, to add data to the database, you should use the following lines of code:

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:

In this way, you can add as many places as you want. So, you'll have a database structure that will look like this:

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

为了更清楚，请看下图:

To be more clear, please see the image below:

如果要查询数据，需要使用Query对象.

If you want to query the data, you need to use a Query object.

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

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

But because I only have a few records in the database, I will use only the placesRef CollectionReference.

假设您已经有一个ListView"在您的 .XML 文件中，如下所示:

Assuming you already have a "ListView" in your .XML file that looks like this:

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

要显示数据，首先需要创建一个适配器类.这个类应该是这样的:

To display the data, first you need to create an adapter class. This class should look like this:

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;
    }
}

然后在您的 onCreate() 方法中使用以下代码:

Then in your onCreate() method use the following code:

ListView mListView = (ListView) findViewById(R.id.place_list);
PlacesAdapter placesAdapter = new PlacesAdapter(getApplicationContext(), randomPlaceList);
mListView.setAdapter(placesAdapter);

然后立即获取数据并将更改通知适配器:

And right after that, get the data and notify the adapter about the changes:

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)));
            }
            placesAdapter.notifyDataSetChanged();
        }
    }
});

每次启动应用时，ListView 中的结果将是 3 个随机位置.

The result in your ListView will be, 3 random places each time you start your app.

这篇关于什么错过了，连接 Firestore 和 ListView 以获得样本中的随机结果?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！