问PHP：如何在表单注册后显示表单错误消息

EN

<?php 
class Register
{   
    private $_db;
    public function __construct()
    {
        $this->_db = new Connection();
        $this->_db = $this->_db->dbConnect();
    }
    public function CheckUname($username,$email,$password,$groups,$level)
    {
        if(!empty($username)&&!empty($email)&&!empty($password)&&!empty($groups)&&!empty($level))
        {
            $chk1 = $this->_db->prepare("SELECT user_name FROM admins WHERE user_name = ?");
            $chk1->bindParam(1,$username);
            $chk1->execute();
            if($chk1->rowCount() == 1)
            {
                $notice['username_exists'] = "Try different username";
            }else{
                $chk2 = $this->_db->prepare("SELECT email_address FROM admins WHERE email_address = ?");
                $chk2->bindParam(1,$email);
                $chk2->execute();
                if($chk2->rowCount() == 1)
                {
                    $notice['email_exists'] = "The email address that you have entered is already exists in database";
                }else{
                    $this->NewAdmin($username,$email,$password,$groups,$level);
                    $notice['success_message'] = "New admin was successfully added";
                }
            }
        }
    }
    public function NewAdmin($username,$email,$password,$groups,$level)
    {
        if(!empty($username)&&!empty($email)&&!empty($password)&&!empty($groups)&&!empty($level))
        {
            $reg = $this->_db->prepare("INSERT INTO admins (user_name, email_address, password_hash, group_admin, date_joined, admin_level) VALUES ( ?, ?, ?, ?, NOW(), ?)");
            $reg->bindParam(1,$username);
            $reg->bindParam(2,$email);
            $reg->bindParam(3,$password);
            $reg->bindParam(4,$groups);
            $reg->bindParam(5,$level);
            $reg->execute();
        }
    }
}
?>

<?php 
if(isset($notice['email_validation'])){
echo "
<div class='alert alert-danger'>
    <strong>Hey!</strong> ".$notice['email_validation'].".
</div>
";
}
if(isset($notice['username_exists'])){
echo "
<div class='alert alert-danger'>
    <strong>Hey!</strong> ".$notice['username_exists'].".
</div>
";
}
if(isset($notice['email_exists'])) {
echo "
<div class='alert alert-danger'>
    <strong>Hey!</strong> ".$notice['email_exists'].".
</div>
";
}
if(isset($notice['success_message'])) {
echo "
<div class='alert alert-success'>
    <strong>Hey!</strong> ".$notice['success_message'].".
</div>
";
}
?>