Replatform Retrospective

So you don't make the same mistakes.

Over the past couple of weeks I re-built MinimalBible fully on top of Android Studio. Previously when starting this project, I used Eclipse for a couple reasons. First being Eclipse was what was currently used in production. Second, the foundational library I rely on (jSword) was an existing Java library, so I would have to engineer the Gradle build myself to make it compatible with Android Studio.

Now all this was well and good, but I eventually wanted to migrate to Android Studio. It was new and robust, could do cool things, didn't have to mess with plugins, etc. After having used Android Studio for a while, it seems like most reputable libraries are moving there. Plus, IntelliJ is simply a better IDE than is Eclipse.

However, the migration process ended up being fairly challenging. I spent days migrating the jSword build to Ant, plus figuring out the random paths in the build.gradle file, plus the apt library for annotation processing... But the straw that broke the camel's back was testing. I had so many problems figuring out how to make Unit Tests work, I eventually gave up. It was time for a re-design, and I'm glad I did.

So, MinimalBible was built from the ground-up all over again. It ended up not being nearly as time-consuming or complicated as I expected. But, here's some of the lessons I've learned in the process. The idea is that nobody should have to make these errors again.

Lesson 1: Keep testing in mind

One of the things I was looking forward to in switching to Android Studio was getting testing working. The way I had originally structured the application, it was borderline impossible to use Mock objects. Here's the problem in a nutshell:

Problem:

• Everything being injected needs to get access to the objects it is being injected with
• Using the Application object seems like a good idea - it's available globally, so we can store all the dependencies there.
• There's no way to swap out the Application instance during testing to provide mock objects. And any modifications done to the instance (like forcibly over-riding objects) are global - it becomes impossible to guarantee a consistent environment.

Solution:

Build in testing from the start. It's been really helpful for me to be able to change code and still have a sanity check to make sure I didn't break anything. My code coverage right now is still terrible, but I have a platform to make sure I can actually do this going forward.

Lesson 2: Static objects are awful

Every enterprise application I've worked on, and most Android applications, all have a dependency injection system of some form. I've previously outlined a number of them, but I settled on Dagger.

Problem:

• Many times you need to ensure that only one instance of an object exists during execution
• Add a static method to retrieve an instance of the object - everyone goes through the static method
• This guarantees testing is impossible - you can't ever change the static method everyone else relies on. Thus, you can test that method, but never change it.

Solution:

Use your dependency injector the way it was meant to be used. I'm talking as few static references to anything as possible. Two examples of how I do this:

Configuration as code:

Both modules provide a singleton list that is used as configuration. It will not change during the application lifecycle, and I probably won't touch it again during development. But if I want to test how the objects inside the list are used, I can. This isn't possible if the "valid categories" are a static list.

MainConfig.java:

@Module()
class MainConfig {
    @Provides @Singleton
    List<BookCategory> provideValidCategories() {
        List<BookCategory> categoryList = new ArrayList<BookCategory>();
        categoryList.put(Category1);
        categoryList.put(Category2);
        return categoryList;
    }
}

TestConfig.java:

@Module()
class TestConfig {
    @Provides @Singleton
    List<BookCategory> provideValidCategories() {
        List<BookCategory> categoryList = new ArrayList<BookCategory>();
        categoryList.put(mockCategory1);
        return categoryList;
    }
}

Dynamic Injection references:

I've been talking a lot about testing, and here's some more. Bear with me.

One of the problems I ran into during testing was how objects being injected got access to the graph of their dependencies. Previously, I would call something like MyApp.inject(this), relying on a static reference to MyApp. Instead, each object should be given a interface that they can inject from, and you can worry about the interface implementation elsewhere. Consider the below:

MyFragment.java

class MyFragment extends Fragment() {
    public static MyFragment newInstance(Injector i) {
        MyFragment f = new MyFragment();
        i.inject(f);
        return f;
    }
}

MyActivity.java

class MyActivity extends Activity implements Injector {
    // We're going to assume that the ObjectGraph is created
    // elsewhere
    private ObjectGraph mObjectGraph;
    private void inject(Object o) {
        mObjectGraph.inject(o);
    }
   
    @Override
    public void onCreate(Bundle savedInstanceState) {
        MyFragment f = MyFragment.newInstance(this);
    }
}

MyActivityTest.java

class MyActivityTest extends TestCase implements Injector {
    // Again, created elsewhere
    private ObjectGraph mObjectGraph;
    private void inject(Object o) {
        mObjectGraph.inject(o);
    }
   
    public void testMyFragment() {
        MyFragment f = MyFragment.newInstance(this);
        // Actually do the testing stuff...
    }
}

Injector.java

interface Injector {
    public void inject(Object o);
}

So now after all this code we have a Fragment that can be injected by both the actual activity, or run in isolation with a TestCase. Nice.

Lesson 3: Design choices matter

Probably the most important lesson I can convey: If you see a bad pattern, now is the time to fix it. There were a number of different things that this re-platform allowed me to fix, and apply lessons that I've learned. And working in enterprise, I've seen how challenging it is to refactor code that's stuck in a broken design pattern. Every bit of time put in to make sure you start with good design pays incredible dividends.

So if you think that you have a better design idea, now's the time to make it happen. Don't let technological cruft build up, be ruthless about cutting that junk out. If you see a problem early, fix it. There are so many ways to get the point across, but it really is that important.

Conclusion

I learned a lot from re-implementing MinimalBible, and it's been great being able to re-think and start fresh. Plus, catching these things early makes life so much easier later on.

Hope this is helpful for making sure you can avoid issues in the future!