致命错误:在非对象上调用成员函数rowCount()

我在我的登录中使用PDO(之前通过sqli指示),我尝试了以下内容,但是我得到了这个致命错误,并且无法弄清楚要给它什么,所以它满足了错误:

if($query->rowCount() > 0) 
{
   // session stuff
   // refresh page
}

然后我尝试了这个:

if($query->rowCount() == 1) 
{
   // session stuff
   // refresh page
}

但我仍然得到这个:致命错误:在非对象上调用成员函数rowCount()

这是我在改变之前开始的:

$count = $query->rowCount();

最后,这是一个更好的代码片段,以便您可以了解所涉及的内容:

prepare("SELECT * FROM members WHERE username = ? OR email = ?");
            $query = $query->execute(array(
            $username,
            $email
        ));

        $count = $query->rowCount();

        if($count == 0) {
            $query = $dbc->prepare("INSERT INTO memebers SET username = ?, email = ?, password = ?");
            $query = $query->execute(array(
                $username,
                $email,
                $password
            )); 
            if($query) {
                echo "Your account has been registered, you may login!";                
        }           
        }
        else {
            echo "A user already exists with that username/password.";
        }
    }
    else {
            echo "Your passwords do not match!";
        }
}
else {
            echo "Invalid email address!";
        }
    }           
?>

任何人都可以指出我在这里出错的地方.这是我抛出的唯一错误.