The inversion of control (IoC) container is a tool for managing class dependencies. Dependency injection is a method of removing hard-coded class dependencies. Instead, the dependencies are injected at run-time, allowing for greater flexibility as dependency implementations may be swapped easily.
There are two ways the IoC container can resolve dependencies: via Closure callbacks or automatic resolution. First, we'll explore Closure callbacks. First, a "type" may be bound into the container:
App::bind('foo', function($app) {
return new FooBar;
});
$value = App::make('foo');
When the App::make method is called, the Closure callback is executed and the result is returned.
Sometimes you may wish to bind something into the container that should only be resolved once, and the same instance should be returned on subsequent calls into the container:
App::singleton('foo', function() {
return new FooBar;
});
You may also bind an existing object instance into the container using the instance method:
$foo = new Foo;
App::instance('foo', $foo);
In some cases, a class may depend on an interface implementation, not a "concrete type". When this is the case, the App::bind method must be used to inform the container which interface implementation to inject:
App::bind('UserRepositoryInterface', 'DbUserRepository');
Now consider the following code:
$users = App::make('UserRepositoryInterface');
Since we have bound the UserRepositoryInterface to a concrete type, the DbUserRepository will automatically be injected into this controller when it is created.
IoC bindings, like event handlers, generally fall under the category of "bootstrap code". In other words, they prepare your application to actually handle requests, and usually need to be executed before a route or controller is actually called. The most common place is the boot method of a Plugin registration file. Alternatively, plugins can supply a file named init.php in the plugin directory that you can use to place IoC registration logic.
Service providers are a great way to create libraries and perform group related IoC registrations in a single location. Within a service provider, you might register a custom authentication driver, register your application's repository classes with the IoC container, or even setup a custom Artisan command.
In fact, plugin registration files inherit service providers and most of the core components include service providers. All of the registered service providers for your application are listed in the providers array of the config/app.php configuration file.
To create a service provider, simply extend the October\Rain\Support\ServiceProvider class and define a register method:
use October\Rain\Support\ServiceProvider;
class FooServiceProvider extends ServiceProvider
{
public function register()
{
$this->app->bind('foo', function() {
return new Foo;
});
}
}
Note that in the register method, the application IoC container is available to you via the $this->app property. Once you have created a provider and are ready to register it with your application, simply add it to the providers array in your app configuration file.
You may also register a service provider at run-time using the App::register method:
App::register('FooServiceProvider');
You can register special events before a requested is routed using the before and after methods:
App::before(function ($request) {
// Code to execute before the request is routed
});
App::after(function ($request) {
// Code to execute after the request is routed
});
The service container fires an event each time it resolves an object. You may listen to this event using the resolving method:
App::resolving(function ($object, $app) {
// Called when container resolves object of any type...
});
App::resolving('foo', function ($fooBar, $app) {
// Called when container resolves objects using hint "foo"...
});
App::resolving('Acme\Blog\Classes\FooBar', function ($fooBar, $app) {
// Called when container resolves objects of type "FooBar"...
});
As you can see, the object being resolved will be passed to the callback, allowing you to set any additional properties on the object before it is given to its consumer.
You may use the environment method to discover the application environment as determined by the environment configuration.
// production
App::environment();
It is possible to know if the current request is being performed in the administrative back-end area using the runningInBackend method.
App::runningInBackend();
You may also use the runningInConsole method to check if the executing code is taking place inside the command line interface:
App::runningInConsole();