> Symfony 7 > Dependency Injection #[Attributes]
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03.

Simplify with AutoconfigureTag and AsTaggedItem

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In the last chapter, we refactored the big switch statement in our controller to this little try-catch. Our remote works the same way it did before, but now we're using the Command pattern. We also used this AutowireLocator attribute to tell Symfony how to wire up this container. This is great, but what if I told you we could simplify this even more?

#[AutoconfigureTag]

Since all of our buttons implement this ButtonInterface, we'll add our second dependency injection attribute: #[AutoconfigureTag]:

12 lines | src/Remote/Button/ButtonInterface.php
// ... lines 1 - 6
#[AutoconfigureTag]
interface ButtonInterface
// ... lines 9 - 12

This attribute tells Symfony:

Hey, add a tag to any service that implements this interface!

Service Tags

A tag is just a string that's connected to a service, and by itself, it doesn't really do anything. But, now that our services have this tag, we can replace the manual service mapping we use in ButtonRemote's #[AutowireLocator] attribute with the tag name:

22 lines | src/Remote/ButtonRemote.php
// ... lines 1 - 10
public function __construct(
#[AutowireLocator(ButtonInterface::class)]
private ContainerInterface $buttons,
) {
// ... lines 15 - 22

When you use the #[AutoconfigureTag] attribute, you can customize the tag name. If you choose not to, the interface name will be used by default. We'll just stick with the default name because the name isn't super important.

Okay, back in our browser, let's see if everything still works. Press a button and... error.

Button "power" not found.

Scroll down to see the exception details. Ah, here it is! This "not found" exception was thrown from the press() method because it couldn't find "power" in ButtonRemote's container. Luckily, the previous exception details shows us the service IDs it did find - the full class names of our buttons. So they are being wired up, but not by the ID we need.

#[AsTaggedItem]

We want the service ID's of our container to be the slug names of our buttons. To do this, we'll use our next dependency injection attribute: #[AsTaggedItem]. Putting this on the implementations of ButtonInterface allows us to customize the service ID.

Start with the ChannelDownButton. Add #[AsTaggedItem] to the class... and for the first argument, which is the index, we'll write channel-down.

15 lines | src/Remote/Button/ChannelDownButton.php
// ... lines 1 - 6
#[AsTaggedItem('channel-down')]
final class ChannelDownButton implements ButtonInterface
// ... lines 9 - 15

We'll do the same thing in ChannelUpButton... PowerButton... VolumeDownButton... and VolumeUpButton.

15 lines | src/Remote/Button/ChannelUpButton.php
// ... lines 1 - 6
#[AsTaggedItem('channel-up')]
final class ChannelUpButton implements ButtonInterface
// ... lines 9 - 15

15 lines | src/Remote/Button/PowerButton.php
// ... lines 1 - 6
#[AsTaggedItem('power')]
final class PowerButton implements ButtonInterface
// ... lines 9 - 15

15 lines | src/Remote/Button/VolumeDownButton.php
// ... lines 1 - 6
#[AsTaggedItem('volume-down')]
final class VolumeDownButton implements ButtonInterface
// ... lines 9 - 15

15 lines | src/Remote/Button/VolumeUpButton.php
// ... lines 1 - 6
#[AsTaggedItem('volume-up')]
final class VolumeUpButton implements ButtonInterface
// ... lines 9 - 15

All right, spin back over to your browser... refresh the page... press a button, and... it works! If we look at the profiler, we can see that it's dumping the correct message for the button.

So now, whenever we want to add a new button, we just need to create the button class, have it implement the ButtonInterface, and add the #[AsTaggedItem] attribute with a unique button name.

If we want this to show up in our remote UI, we still need to add it to our template. But what if we could do even better? What if we didn't have to edit this file every time we add a new button? To do that, we need to use another dependency injection attribute. That's next.