java - 如何在Firebase中获取 child 的数据

Question

我的数据库树结构如下:

如果我有“userid”的值，请告诉我如何获取“username”的值

Answer 1

how do I get the value of "username" if I have the value of "userid"

要解决此问题，请使用以下代码行:

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference uidRef = rootRef.child("users").child(uid);
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        String username = dataSnapshot.child("username").getValue(String.class);
        Log.d(TAG, username);
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};
uidRef.addListenerForSingleValueEvent(valueEventListener);

logcat 中的输出将是:

hisoka