自己写的yii 独立验证器不能使用

namespace app\models;

use Yii;
use yii\base\Model;

class RegisterForm extends Model
{

public $email;
public $password;
public $password_repeat;

public function rules()
{
    return [
        [['email', 'password', 'password_repeat'], 'required'],
        ['email', 'email'],
        //['email', 'unique', 'targetClass' => '', 'message' => '邮箱名已存在。'],
        [['password', 'password_repeat'], 'string', 'length' => [6, 20]],
        ['password', 'checkPassword'],
        ['password_repeat','compare','compareAttribute' =>'password','message'=>'两次输入的密码不一致。'],
    ];
}

public function register()
{
    //处理一些东西
    //注册相关的
    return false;
}

public function attributeLabels()
{
    return [
        'email' => '邮箱',
        'password' => '密码',
        'password_repeat' => '重复密码',
    ];
}

public function checkPassword($attribute, $params)
{
    if (!ctype_alnum($this->$attribute)) {
        $this->addError($attribute, '必须包含字母或数字。');
    }
}

}

checkPassword 这个独立验证器 使用不了 我代码书写有问题吗 各位大哥们

---

写法是正确的，你是凭什么判定不能使用的呢？

这是我的测试用例：

class TestModel extends \yii\base\Model
{
    public $password;

    public function rules()
    {
        return [
            ['password', 'checkPassword']
        ];
    }

    public function checkPassword($attribute, $params)
    {
        if (!ctype_alnum($this->$attribute)) {
            $this->addError($attribute, 'password error');
        }
    }
}

test case1:

$model = new TestModel();
$model->password = '1121312&&UJ9123/.';

$model->validate();

var_dump($model->getErrors()); //会打印出有错误

test case 2:

$model = new TestModel();
$model->password = '1121312';

$model->validate();

var_dump($model->getErrors()); //无错误