IoC

I just watched an Inversion of Control course on Pluralsight. I get it now, but I’m writing this down to make sure I get it tomorrow.

• Dependency Inversion Principle - accessed items should not depend on accessor items
• Inversion of Control
  • a pattern to “solve” the Dependency Inversion Principle
  • accessor tells accessed how they will interact
  • Interface inversion - accessor creates interface rather than accessed
  • Flow inversion - event-driven instead of procedural programming
  • Creation inversion - object is created outside of the class it is used in -
    • factory pattern (Button button = ButtonFactory.CreateButton();)
    • service locator (Button button = ServiceLocator.Create(IButton.class);)
    • dependency injection
• Dependency Injection
  • dependency is created outside of class that depends on it
  • differs from creation inversion because it specifies that the dependency is not created by the dependent; in e.g. the factory pattern, the dependent is still responsible for creating the dependent by calling the factory
  • Constructor Injection
    • most common
    • dependency is passed into constructor and stored as field in object
  • Setter Injection
    • dependency is passed into setter and stored as field in object
  • Interface Injection
    • class has interface which requires a setter
    • when calling cast the class as the interface and call the interface’s setter
    • more explicit than just a setter
• IoC Container
  • framework for doing dependency injection
  • resolves the chain of dependencies

They aren’t difficult concepts. Really, the most difficult part is keeping all the terminology straight.