Dependency Injection (A kind of IoC) is a design principle that had been quite popular among designers, a few years ago. Well, it does not mean that it is not popular any more. How useful is it? There is no exact estimation study. I have seen a few papers trying to investigate benefits precisely but failed due to less awareness of development teams. However, it is very much acceptable that it improves maintainability and makes unit tests much easier at the cost of a light weight container.

All objects of a computer software make a graph that shows relationships among several objects. More complex is the graph, more complex will be the software. More complex software programs are harder to maintain and provide very little margin to accommodate future changes (Less flexible). DI provide us a mechanism to loosen ties between objects in the graph. Loose coupling can be achieved in several different ways, I have discussed different approaches and their pros & cons in my presentation. Associated code can be downloaded here.