Dependency Injection¶
TYPO3 uses a Dependency Injection solution based on the corresponding PSR-11 compliant Symfony component to standardize object initialization throughout the core as well as in extensions.
The recommended way of injecting dependencies is to use constructor injection:
public function __construct(Dependency $dependency)
{
$this->dependency = $dependency;
}
By default all classes shipped by the TYPO3 core system extensions are available for dependency injection.
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Configure Dependency Injection in Extensions¶
Extensions have to configure their classes to make use of the
dependency injection. This can be done in Configuration/Services.yaml
.
Alternatively Configuration/Services.php
can be used.
# Configuration/Services.yaml
services:
_defaults:
autowire: true
autoconfigure: true
public: false
Your\Namespace\:
resource: '../Classes/*'
This is how a basic Services.yaml
of an extension looks like. The meaning of autowire
,
autoconfigure
and public
will be explained below.
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Whenever service configuration or class dependencies change, the core cache needs to be flushed to rebuild the compiled Symfony container.
Autowire¶
autowire: true
instructs the dependency injection component
to calculate the required dependencies from type declarations. This works for constructor
and inject methods. The calculation yields to a service initialization recipe
which is cached in php code (in TYPO3 core cache).
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An extension doesn't need to use autowiring, it is free to manually wire dependencies in the service configuration file.
Autoconfigure¶
It is suggested to enable autoconfigure: true
as this will automatically
add Symfony service tags based on implemented interfaces or base classes.
For example autoconfiguration ensures that classes which implement
\TYPO3\CMS\Core\SingletonInterface
will be publicly available from the
Symfony container.
Public¶
public: false
is a performance optimization and is therefore suggested to be
set in extensions. This settings controls which services are available
through \Psr\Container\ContainerInterface->get()
. However some classes, that need to
be public, will be marked public automatically due to autoconfigure: true
.
These classes include Singletons, because they need to be shared with code that uses
\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance()
and Extbase controllers.
Knowing what to make public¶
Instances of \TYPO3\CMS\Core\SingletonInterface
and Extbase controllers are
marked public by default. Additionally some classes cannot be private as well.
As the Symfony documentation puts it:
"Simply said: A service can be marked as private if you do not want to access it directly from your code."
—Official documentation for public and private services.
Direct access includes instantiation via \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance()
.
This means every class that should make use of dependency injection and is not instantiated via injection
itself but by e.g. \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance()
have to be marked
as public. Some examples for this are:
- User Functions
- Non-Extbase Controllers
- Classes registered in Hooks
For such classes an extension can override the global public: false
configuration in the
Configuration/Services.yaml
for each class.
# Configuration/Services.yaml
services:
_defaults:
autowire: true
autoconfigure: true
public: false
Vendor\MyExtension\:
resource: '../Classes/*'
Vendor\MyExtension\UserFunction\ClassA:
public: true
With this configuration you can use dependency injection in \Vendor\MyExtension\UserFunction\ClassA
when it is created in the context of a USER
TypoScript object which would not be possible if this
class was private.
Errors resulting from wrong configuration¶
When objects using dependency injection are not configured properly, one or more
of the following issues can be the result. In such a case, check whether the
class has to be configured as public: true
.
ArgumentCountError
is raised on missing dependency injection for
Constructor Injection:
(1/1) ArgumentCountError
Too few arguments to function Vendor\ExtName\Namespace\Class::__construct(),
0 passed in typo3/sysext/core/Classes/Utility/GeneralUtility.php on line 3461 and exactly 1 expected
An Error
is raised on missing dependency injection for
Method Injection, once the dependency is used within the code:
(1/1) Error
Call to a member function methodName() on null
Supported Ways of Dependency Injection¶
Classes should be adapted to avoid both, \TYPO3\CMS\Extbase\Object\ObjectManager
and
\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance()
whenever possible.
Class dependencies should be injected via constructor injection or
setter methods.
Constructor Injection¶
A class dependency can simply be specified as a constructor argument:
public function __construct(Dependency $dependency)
{
$this->dependency = $dependency;
}
Method Injection¶
As an alternative to constructor injection injectDependency()
Methods can be used.
Additionally a setDependency()
will also work if it has the annotation @required
:
/**
* @param MyDependency $myDependency
*/
public function injectMyDependency(MyDependency $myDependency)
{
$this->myDependency = $myDependency;
}
/**
* @param MyOtherDependency $myOtherDependency
* @required
*/
public function setMyOtherDependency(MyOtherDependency $myOtherDependency)
{
$this->myOtherDependency = $myOtherDependency;
}
Interface Injection¶
It is possible to inject interfaces as well. If there is only one implementation for a certain interface the interface injection is simply resolved to this implementation:
public function __construct(DependencyInterface $dependency)
{
$this->dependency = $dependency;
}
When multiple implementation of the same interface exist, an extension needs to specify which implementation should be injected when the interface is type hinted. Find out more about how this is achieved in the official Symfony documentation.
Further Information¶
- Symfony dependency injection component
- Symfony service container
- t3core:Changelog/10.0/Feature-84112-SymfonyDependencyInjectionForCoreAndExtbase of the TYPO3 core.