dependency injection - What are the specific benefits of using DI on Android?

Question

What are the specific benefits or advantages of using a dependency injection framework for Android, like Dagger, Transfuse or RoboGuice?

For example, what kind of apps would benefit the most from using DI? is there more of a performance advantage, or is it more on the ease of extending an app, or even more about making it testable?

One of the reasons for asking this is to gauge if an app I'm developing would actually benefit from it or not much. Since I intend the app to be serious at some point, testability and ease of extension would be great, even if costly to use (more time to setup, learning curve, etc) for the first versions.

Thanks!

Answer 1

For example, what kind of apps would benefit the most from using DI?

Dependency injection (as a pattern not a library) benefits almost all code.

• It promotes designing modular components which expose only the necessary APIs required to perform a specific action. When you are forced to break up pieces of your applications you have to consider how much implementation detail to expose, how the API behaves, and the visibility of classes and methods.
• It promotes logical abstractions of components (think: interfaces and their implementations). You certainly don't have to do this, but it ends up occurring organically anyway the more you DI things.
• It facilitates testability by creating a single point of type consumption through which a class obtains something it needs. Need to swap out a Foo for a TestFoo? No problem.

Is there more of a performance advantage?

No. The dependency injection libraries exist solely to reduce boilerplate around the pattern and increase the declarative ability to request dependencies.

Is it more on the ease of extending an app?

Absolutely. While I would never recommend using Guice (or RoboGuice) in an Android application, the introductory talk to Guice from Google I/O is a fantastic introduction to why dependency injection is important in this regard.

Even more about making it testable?

Yes and no. This is a happy side-effect of proper abstraction and modularization. Testing is a great thing so the fact that dependency injection offers an ease into it is also great.

I gave a talk about Dagger in the context of Android recently which you can watch* or view the slides. The talk starts out with dependency injection as a pattern and then moves into how Dagger reduces the boilerplate and enables some pretty cool features as well.

I also made a fairly advanced sample application which leverages Dagger for complex injection use-cases that might also be worth checking out.

_{*The talk is currently not free, but will become so at some point in the next 10 months.}