[TYPO3-dev] Re: Best-practice: dependencies in Controllers

[Philipp]

If in extbase context:

get instance of objectmanager with
$objectManager = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance('\TYPO3\CMS\Extbase\Object\ObjectManager');

then load your singleton classes with 
$objectManager->get('Vendor\\Extension\\Path\\To\\Class');

to instanciate new prototypes use
$objectManager->create('Vendor\\Extension\\Path\\To\\Model',$construcotArgument1,$constructorArgument2);

If you want an instance of a very simple class with no dependencies, etc simply use 
$object = new \Vendor\Package\Path\To\Model($arg1,$arg2);

if you are in ControllerContext or a Repository you allready have an injected ObjectManager
$this->objectManager->get()...

A singleton class is a class that must not exist multiple, only one instance is allowed. You need that for example when using a sessioncache or something within the class. Therefore a singleton class must not have a contructor. To make clear that a variable represents a singleton you use objectManager->get and not objectManager->create

When asking the objectManager for a singleton class it allways returns you the same instance.

You can define a singleton class by implementing the singleton interface \TYPO3\CMS\Core\SingletonInterface

When you need some coreclass not related to extbase you can call it directly using makeInstance.