从Firebase数据库实时读取

Question

我只是想从数据库中读取“ one”的值，该错误是选择了空对象

以这种方式尝试，问题仍然存在；这是数据库

String toz = "";
private String showData(DataSnapshot dataSnapshot, String name) {
    for (DataSnapshot ds : dataSnapshot.getChildren()) {
        getCarNum numm = new getCarNum("7");
        myRef.child("NumberOfCars").child(name).setValue(numm);
        getCarNum uInfo = new getCarNum();
        if (dataSnapshot.child("NumberOfCars").child(name).child("num").exists()) {
            uInfo.setnum(ds.child("NumberOfCars").child(name).getValue(getCarNum.class).getnum()); //get the one
            toz = uInfo.getnum();
            Log.w("Test", toz+"");
        }
        else
        {
            Log.w("kda mafish el user da", "tooooz" );
        }
    }
    return toz;
}

预期结果：7 实际结果：空指针异常时出错。