搜索不能在yii2中使用单独的搜索模型

namespace app\models;

use yii\base\Model;
use yii\data\ActiveDataProvider;
use app\models\Post;

class PostSearch extends Post
{
    public function rules()
    {
        return [
            [['title', 'content'], 'safe'],
        ];
    }

    public function search($params)
    {
        $query = Post::find();

        $dataProvider = new ActiveDataProvider([
            'query' => $query,
        ]);

        if (!$this->load($params) || !$this->validate()) {
            return $dataProvider;
        }

        $query->andFilterWhere(['like', 'title', $this->title])
            ->andFilterWhere(['like', 'content', $this->content]);

        return $dataProvider;
    }
}

namespace app\controllers;

use Yii;
use yii\web\Controller;
use app\models\PostSearch;

class PostController extends Controller
{
    public function actionIndex()
    {
        $searchModel = new PostSearch();
        $dataProvider = $searchModel->search(Yii::$app->request->queryParams);

        return $this->render('index', [
            'searchModel' => $searchModel,
            'dataProvider' => $dataProvider,
        ]);
    }
}