orderByChild（）。equalTo（）未返回ID

Question

 LiveData<DataSnapshot> questBadgeData = questViewModel.getBadgeSnapshotLiveData(questViewModel.getQuestId());
    Log.d("sad","score calc quest id "+questViewModel.getQuestId());
    questBadgeData.observe(getViewLifecycleOwner(), new Observer<DataSnapshot>() {
        @Override
        public void onChanged(DataSnapshot dataSnapshot) {
            String badgeID = dataSnapshot.getKey();
            Log.d("sad","badge id "+badgeID);
            //String icon = dataSnapshot.child("icon").getValue().toString();
            //String name = dataSnapshot.child("name").getValue().toString();
            //questViewModel.setBadgeData(badgeID,icon,name);
            questViewModel.setBadgeData(badgeID,"dummy","dummy");
        }
    });

这是我的Firebase数据库的结构：

 @NonNull
public LiveData<DataSnapshot> getBadgeSnapshotLiveData(String qid) {
    Query query = dbBadge.orderByChild("questid").equalTo(qid);
    return new FirebaseQueryLiveData(query);
}

这是我的FirebaseQueryLiveData类

public class FirebaseQueryLiveData extends LiveData<DataSnapshot> {
private static final String TAG = "FirebaseQueryLiveData";

private final Query query;
private final MyValueEventListener listener = new MyValueEventListener();

public FirebaseQueryLiveData(Query query) {
    this.query = query;
}

public FirebaseQueryLiveData(DatabaseReference ref) {
    this.query = ref;
}

@Override
protected void onActive() {
    Log.d(TAG, "onActive");
    query.addValueEventListener(listener);
}

private class MyValueEventListener implements ValueEventListener {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        setValue(dataSnapshot);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.e(TAG, "Can't listen to query " + query, databaseError.toException());
    }
}

}

据我所知，当我打印日志中的批次ID时，我应该得到'b1'，而当questid ='q1'时，我应该得到'b1'。

2020-06-30 17:15:21.864 29487-29487/com.example.activedash D/sad: score calc quest id q1
2020-06-30 17:15:21.916 29487-29487/com.example.activedash D/sad: badge id badge

当我只是将密钥作为child（key）而不是orderByChild（）时，这很好，但是我需要通过orderByChild（）获取徽章的密钥

 @NonNull
public LiveData<DataSnapshot> getBadgeSnapshotLiveData(String qid) {
    Query query = dbBadge.child("b1");
    return new FirebaseQueryLiveData(query);
}

Answer 1

对Firebase数据库执行查询时，可能会有多个结果。因此，快照包含这些结果的列表。即使只有一个结果，快照也会包含一个结果的列表。

您的onDataChange需要通过遍历dataSnapshot.getChildren()来处理该列表。因此，如果您确实只期望得到一个结果，那就是：

public void onDataChange(DataSnapshot dataSnapshot) {
    for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
        setValue(snapshot);
    }
}