Undefined variable: pattern in yii ,preg_match

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PHP

Hi,all.
I do is extending the CValidator class,
when run , Undefined variable: pattern error.
where problem?


/**
* @return array validation rules for model attributes.
*/
public function rules()
{
return array(
array('password', 'ext.MyValidators.passwordStrength', 'strength'=>self::STRONG),
);
}



class passwordStrength extends CValidator
{
public $strength;

private $weak_pattern='/^(?=.*[a-zA-Z0-9]).{5,}$/';
private $strong_pattern= '/^(?=.*\d(?=.*\d))(?=.*[a-zA-Z](?=.*[a-zA-Z])).{5,}$/';


/**
* Validates the attribute of the object.
* If there is any error, the error message is added to the object.
* @param CModel $object the object being validated
* @param string $attribute the attribute being validated
*/
protected function validateAttribute($object,$attribute)
{

// check the strength parameter used in the validation rule of our model
if ($this->strength == 'weak')
$pattern = $this->weak_pattern;
elseif ($this->strength == 'strong')
$pattern = $this->strong_pattern;

// extract the attribute value from it's model object
$value=$object->$attribute;

if(!preg_match($pattern, $value))
{
$this->addError($object,$attribute,'your password is too weak!');
}
}

/**
* Returns the JavaScript needed for performing client-side validation.
* @param CModel $object the data object being validated
* @param string $attribute the name of the attribute to be validated.
* @return string the client-side validation script.
* @see CActiveForm::enableClientValidation
*/
public function clientValidateAttribute($object,$attribute)
{

// check the strength parameter used in the validation rule of our model
if ($this->strength == 'weak')
$pattern = $this->weak_pattern;
elseif ($this->strength == 'strong')
$pattern = $this->strong_pattern;

$condition="!value.match({$pattern})";

return "
if(".$condition.") {
messages.push(".CJSON::encode('your password is too weak, you fool!').");
}";
}

}



Thanks.