怎么在controller里把参数传给model 的function fileds() [ 2.0 版本 ]

Controller.php

<?php
namespace frontend\controllers;

use frontend\models\Test;
use yii\rest\Controller;

class TestController extends Controller {

    public function actionIndex($coordinates){
        // 要把$coordinates传到Model
        return Test::find()->all();
    }

}

Model.php

namespace frontend\models;

use yii\db\ActiveRecord;

/**
 *

CREATE TABLE IF NOT EXISTS `test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(250) COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=2 ;

INSERT INTO `test` (`id`, `title`) VALUES
(1, 'hi');

 * Class Test
 * @package frontend\models
 */

class Test extends ActiveRecord {

    public $coordinates;
    public $newField;

    public function rules()
    {
        return [
            [['title'], 'required'],
            [['title'], 'string', 'max' => 250]
        ];
    }

    public function fields()
    {
        $fileds =  parent::fields();
        $fileds['newField'] = function($model,$field){
            // 这里要用到Controller里的$coordinates
            return implode(',',$this->coordinates);
        };
        return $fileds;
    }

}