gistfile1.txt

public function actionIndex($year='')    
{
	if(empty($year)) $year=date('Y'); 
	$searchModel = new TrainingSearch();
	$queryParams = Yii::$app->request->getQueryParams();
	if($year!='all'){
		$queryParams['TrainingSearch']=[
			'year' => $year,
		];
	}
	$queryParams=yii\helpers\ArrayHelper::merge(Yii::$app->request->getQueryParams(),$queryParams);
	$dataProvider = $searchModel->search($queryParams);
	$dataProvider->getSort()->defaultOrder = ['start'=>SORT_ASC,'end'=>SORT_ASC];
	return $this->render('index', [
		'searchModel' => $searchModel,
		'dataProvider' => $dataProvider,
		'year' => $year,
	]);
}

// combobox
$year = ['all', 2016, 2015, 2014, 2013];