Symfony 4 Dependency Injection: Inject into object while creating it in code - php

Question

I'm creating a NavigationBuilder class for my backend. With it, I should be able to add navigation items and then get the html (similar to Symfony's FormBuilder). It is used in a Twig Extension Function.
I have an interface and abstract class for a navigation item (e.g. Nav Link, Divider, Heading, etc.) and I'm creating child classes for these specific items.
For some of these nav items (Link) I need the Symfony Router or RequestStack and I want to inject it into the abstract class so I don't have to pass it as an argument to the constructor of every child class I need it in.
I tried using the method of injecting it with setter methods, because I thought Symfony would do it automatically whenever I create a new object, but obviously that isn't the case.
The NavigationItem class:
namespace App\...\Navigation;
use App\...\NavigationItemInterface;
use Symfony\...\UrlGeneratorInterface;
use Symfony\...\Request;
abstract class NavigationItem implements NavigationItemInterface {
private $router;
private $request;
final public function setRouter(UrlGeneratorInterface $router): self {
$this->router = $router;
return $this;
}
final public function setRequest(Request $request): self {
$this->request = $request;
return $this;
}
final public function matchesCurrentRoute(String $route): Bool {
return $this->getRequest()->get('_route') == $route;
}
/** ... **/
}
My service.yaml file:
App\...\NavigationItem:
class: App\...\NavigationItem
calls:
- method: setRequest
arguments:
- '#request_stack'
- method: setRouter
arguments:
- '#router'
I imagine it to work like this:
$builder = new NavigationBuilder();
$builder
->addItem( new HeaderItem('A Heading') ) // No need for injection
->addItem( new LinkItem('Title', 'route') ) // NEED for injection
->build(); // Returns html
I get this error code:
An exception has been thrown during the rendering of a template ("Notice: Undefined property: App...\DashboardItem::$router").

Answer 1

if you declare a property as private only the class itself, but no child class can use it (directly, that is). declare it protected (talking about the router property in your abstract class) see: https://www.php.net/manual/en/language.oop5.visibility.php
apparently that's not the only problem, and I suppose you confuse dependency injection with auto-wiring. dependency injection only means, that an object doesn't create it's own dependencies, but instead they are from the outside/caller via parameters (in constructor, setters, or specific calls).
auto-wiring works in symfony by either fetching an object from the container (however, by default you always get the same object. but there are ways to define a factory or the option to always retrieve a new object, possibly, not quite sure).