java - 从 firebase 中检索随机节点

Question

编辑

我有一个 firebase 数据库，其中有一棵看起来像这样的树

Stations{
Uknradio
bbcradio1
bbcradio1extra
Beatles radio

然后是一个像这样的 StationsKey 节点

Stations{
Uknradio = true
bbcradio1 =true
bbcradio1extra = true
Beatles radio = true

等等...id喜欢从数据库中拉取一个随机站

这是我使用的代码，给出了新的答案

    String DATABASE_CHILD = "STATIONS";
    String DATABASE_CHILD2 ="STATIONKEY";
    ref = db.getReference().child(DATABASE_CHILD2);
ref.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {

    for (DataSnapshot ds : snapshot.getChildren()) {
     String productId = ds.getKey();
      productIdsList.add(productId);
   }

  int productListSize = productIdsList.size();
    
ref = db.getReference().child(DATABASE_CHILD).child(productIdsList.get(new Random().nextInt(productListSize)));
ref2.addListenerForSingleValueEvent(new ValueEventListener() {
  @Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
    mUrl.clear();
    mTITLE.clear();
    mDOWN.clear();
    mIMAGE.clear();
    mUrl.clear();
    mUP.clear();
    mDESC.clear();

        for (DataSnapshot snap : snapshot.getChildren()) {

            station_items = snap.getValue(Stations_Firebase.class);
            String a  =station_items.getStation();
            String b = station_items.getTag();
            String c = station_items.getUrl();
            Long d = station_items.getUpvote();
            Long e = station_items.getDownvote();
            String f = station_items.getImage();

            mTITLE.add(a);
            mDESC.add(b);
            mUrl.add(c);
            mUP.add(String.valueOf(d));
            mDOWN.add(String.valueOf(e));
            mIMAGE.add(f);
        }

 private int nextInt(int productListSize) {
    return 0;
}

但现在我收到这个错误

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.get(ArrayList.java:437)
    at com.p9p.radioify.ui.station_tabs.Random.getRandomStations(Random.java:103)

Answer 1

编辑:2022 年 8 月 20 日

也许这些其他方法会有所帮助:

• > How to get unique random product in node Firebase?

---

要解决这个问题，请使用以下代码行:

long childrenCount = snapshot.getChildrenCount();
int count = (int) childrenCount;
int randomNumber = new Random().nextInt(count);

然后使用 for 循环使用随机数提取该值:

int i=0;
String themeTune; //Your random themeTune will be stored here
for (DataSnapshot snap : snapshot.getChildren()) {
    if(i = randomNumber) {
        themeTune = snap.getValue(String.class);
        break;
    }
    i++;
}
plysound();