php - Import CSV file to Database using Yii2

one text

I'm trying to import CSV file to the database using yii2 framework.

Controller

public function actionIndex($message=??????)
    {
        // $model = new ProjectDocument;
        //error_reporting(E_ALL);
        //ini_set('display_error', 1);
        $model = new ProjectDocument();

        if ($model->load(Yii::$app->request->post()) ) {
            $model->file = UploadedFile::getInstance($model, 'file');
            // if ($model->load(Yii::$app->request->post())){    
            //  $filename = 'Data.' . $file->extension;
            $upload = $file->saveAs('uploads/' . $filename);
            if ($upload) {
                define('CSV_PATH', 'uploads/');
                $csv_file = CSV_PATH . $filename;
                $filecsv = file($csv_file);
                foreach ($filecsv as $data) {
                    $title = _file[1];
                    $description = $file[2];
                    $phase = $file[3];
                    $modelnew->title = $title;
                    $modelnew->description = $description;
                    $modelnew->phase = $phase;
                    $modelnew->save();
                }
                unlink('uploads/'.$filename);
                return $this->render('create',array('model'=>$model, 'message'=>$message));
            }
        }else{
            return $this->render('create',array('model'=>$model, 'message'=>$message
        ));
        }
        return $this->render('create',array('model'=>$model, 'message'=>$message
    ));
    }

But I getting an error like this,

"Access to undeclared static property: Yii::$app"

Anyone can help me to rectify the error, Thank you in advance..