What is Inversion of Control?

Question

Inversion of Control (IoC) can be quite confusing when it is first encountered.

1. What is it?
2. Which problem does it solve?
3. When is it appropria

Answer 1

I like this explanation: http://joelabrahamsson.com/inversion-of-control-an-introduction-with-examples-in-net/

It start simple and shows code examples as well.

The consumer, X, needs the consumed class, Y, to accomplish something. That’s all good and natural, but does X really need to know that it uses Y?

Isn’t it enough that X knows that it uses something that has the behavior, the methods, properties etc, of Y without knowing who actually implements the behavior?

By extracting an abstract definition of the behavior used by X in Y, illustrated as I below, and letting the consumer X use an instance of that instead of Y it can continue to do what it does without having to know the specifics about Y.

In the illustration above Y implements I and X uses an instance of I. While it’s quite possible that X still uses Y what’s interesting is that X doesn’t know that. It just knows that it uses something that implements I.

Read article for further info and description of benefits such as:

• X is not dependent on Y anymore
• More flexible, implementation can be decided in runtime
• Isolation of code unit, easier testing

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