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
- factory pattern (
- 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.