YII中的Init（）和__constructor

i'm new in YII and I want to set in my constructor something like

public function __construct(Car $car)
{
    $this->car= $car;
}

and use my model to peform the query anything like

public function actionIndex()
{
    $this->car->select('id','color')->all();

    $this->render('index', array( 'car' => $car));
}

If you're using Yii than there is no need to inject $car in controller constructor.

public function actionIndex()
{
    $cars = Car::find()->all();
    return $this->render('index', [
        'cars' => $cars
    ]);
}