为什么Firebase childEventListener不能处理一个引用而处理另一个引用?

参考文献包括:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference usersRef = rootRef.child("users"); 

DatabaseReference TUidRef = usersRef.child(td);

td 从之前的活动中导出如下:

lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        final String dataName = parent.getItemAtPosition(position).toString();
        usersdRef.orderByChild("username").equalTo(dataName).addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for(DataSnapshot data: dataSnapshot.getChildren()){
                    String dataUID = data.child("uid").getValue(String.class);
                    Log.i("uid",dataUID);
                    startActivity(new Intent(Main2Activity.this, Main5Activity.class).putExtra("valueName", dataName).putExtra("valueUID",dataUID));

                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });


    }
});

Bundle bundle = getIntent().getExtras();
td = bundle.getString("valueUID");

这个 childEventListener 使用 usersRef TUidRef 它不会崩溃或者做任何事情,它只是什么都不做。