Firebase 监听器没有被调用

Question

我想检查是否创建了节点。我刚刚在下面用 Toast 调用了，但根本没有烤。

注意：firebase 数据库现在 Total null

  DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

    reference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Toast.makeText(RegisterActivity.this, dataSnapshot.getKey() + "", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(RegisterActivity.this, databaseError.toString() + "", Toast.LENGTH_SHORT).show();
        }
    });

其次是我尝试过但没有运气的代码

 DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

    reference.child("device_id");

    reference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Toast.makeText(RegisterActivity.this, dataSnapshot.getKey() + "", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(RegisterActivity.this, databaseError.toString() + "", Toast.LENGTH_SHORT).show();


        }
    });

Answer 1

更改这行代码：

reference.addListenerForSingleValueEvent(new ValueEventListener() {

与：

reference.child("device_id").addListenerForSingleValueEvent(new ValueEventListener() {