Laravel Dependancy Injection not working

Question

Can someone help me out, everything looks normal, but dependency injection is not working for my class.

On register of this Service Provider, I'm telling Laravel blog is a singleton, and from reading the documentation, this should allow it to resolve when I do line 41.

But it gives me an error saying the following:

Argument 1 passed to 
Aaranmcguire\Blog\Providers\AppServiceProvider::setSettings() must 
be an instance of Aaranmcguire\Blog\Blog, none given, called in 
.../aaranmcguire/Blog/src/Providers/AppServiceProvider.php 
on line 25 and defined

If I remove line 41, then I can successfully DD the class from within the app, confirming its registered.

Any ideas as I've spent almost an hour on this?

@Aaran McGuire Please, don't attach code as images meta.stackoverflow.com/a/285557/5510499. — Vadim Shkaberda
– Vadim Shkaberda, Commented Jul 9, 2016 at 20:21

lagbox · Accepted Answer · 2016-07-10 09:23:42Z

Dependency Injection only happens when using the IoC/Service container to resolve a class or call a method. If you are calling a method yourself and it has required arguments, you have to pass those arguments. Laravel does not change how PHP works.

None of these will ever involve dependency injection as they are direct method calls on an object and do not use the container:

$this->anything(); // just a method call
$something->anything(); // just another method call

The reason you will get constructor dependencies injected is because those particular classes are resolved using the IoC container. Usually the framework is the caller of such code, not you directly. When the framework calls a method on a class, it may use the container to make that call, which is where Method Injection comes into play.

The container has a call method with comment:

"Call the given Closure / class@method and inject its dependencies."

The boot method of Service Providers is called via the IoC container and that method will have dependencies injected as per the Laravel Documentation on Service Providers.

"You are able to type-hint dependencies for your service provider's boot method. The service container will automatically inject any dependencies you need..." Laravel 5.2 Docs - Service Providers - The Boot method

From Illuminate\Foundation\Application@bootProvider:

protected function bootProvider(ServiceProvider $provider)
{
    if (method_exists($provider, 'boot')) {
        return $this->call([$provider, 'boot']);
    }
}

The Application uses the call method to call the boot method on a provider, which is why you can type-hint parameters for the boot method and get Method Injection. It does not directly call boot on the provider object, it uses the container to call it.

To use features of the container, the container has to be used.

-- This is referencing Laravel 5.2, but the IoC is very much the same through the versions.

Aaran McGuire · Accepted Answer · 2016-07-10 07:54:10Z

2

You are mixing binding and method injection.

Binding (singleton):

public function register() {
    $this->app->singleton('blog', function () {
        return new \Blog();
    });
}

public function setSettings() {
    dd($this->app->blog);
}

Method injection:

public function setSettings(\Blog $blog) {
    dd($blog);
}

Edit: Fixing code.

edited Jul 10, 2016 at 7:54

Aaran McGuire

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answered Jul 9, 2016 at 20:05

Bastian Bräu

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2 Comments

Aaran McGuire Over a year ago

Ok, so, why would method injection not work? its saying I'm passing in nothing, which is true because I'm expecting it to inject it. (unless it does not work inside service providers?)

Bastian Bräu Over a year ago

The docs describe method injection as a feature of controllers. So I guess it's only available there. You can just use binding then, by removing line 41.

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