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Injector Android is a project that provides the boilerplate for a testable application.

1. Clone this repository (or download as a .zip)
2. Change the remote to point to your repo
3. Change the package name

• in app/build.gradle line 17
• in app/src/test/resources/robolectric.properties lines 3 and 4
• in app/src/main/AndroidManifest.xml line 2
• (OPTIONAL) in the actual code

• Dependency Injection using Dagger2
• Unit testing using Robolectric 3
• Integration testing using the Android Testing Support Library / Espresso (work in progress)
• AppCompat v7

For the most part, this is standard Dagger2 DI. There is one additional layer that abstracts the fact that we use Dagger from the code, and provides a framework for hierarchical scoping.

This project contains a bare-bones implementation of this concept by providing a narrowing scope of Injectors. This is accomplished through the use of a custom Application class, and a base class for both Activity and Fragment.

Injectors are extensions of Components, and may define extension methods to provide narrower scopes / Injectors.

The top level is the InjectorAndroidApp which has an ApplicationInjector (the ApplicationInjector can be overridden as we'll see when we get to testing). InjectorAndroidApp exposes the ApplicationInjector so that other scopes can use it to get their Injector. A sharedPreferences dependency is provided out of the box; adding more is as simple as adding the dependency to the Component / Injector.

The next scope is at the Activity level, and so ApplicationInjector exposes an extension method to get an ActivityInjector for it:

ActivityInjector extend(BaseActivity activity);

and BaseActivity grabs a reference to that ActivityInjector, injects itself, and exposes it to subclasses:

@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  
  activityInjector = ((InjectorAndroidApp) getApplication()).getInjector().inject(this);
  activityInjector.inject(this);
}

protected ActivityInjector getActivityInjector() {
  return activityInjector;
}

Any subclass of BaseActivity (which should be any Activity in your project) should have an inject(*) method in ActivityInjector, and should retrieve the ActivityInjector in onCreate and inject itself.

So a hypothetical MainActivity would look like this:

public class MainActivity extends BaseActivity {
  @Inject SharedPreferences sharedPreferences;
  
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    
    getActivityInjector().inject(this);
  }
}

And a method would be added to ActivityInjector:

void inject(MainActivity activity);

The next scope is at the Fragment level, and follows the same principles as the Activity scope.

Additional scopes can be added at any level using extension methods, and aside from wiring the Injectors, everything is vanilla Dagger2.

For convenience, this project includes 3 scopes (PerApp, PerActivity, PerFragment) and 3 qualifiers (ForApp, ForActivity, and ForFragment).

Testing is made easier by virtue of overriding the ApplicationInjector with an implementation that replaces the Dagger2 Modules with Modules that return implementations suitable for testing (i.e. mocked instances, etc...).

This project includes the InjectorAndroidRobolectricGradleTestRunner to use as a test runner for Robolectric tests. Aside from providing testing implementations of the Injector hierarchy that returns a mock (using Mockito), it allows for overriding the mocks that will be injected. This can be done by creating a field in your test class that is annotated with OverrideInject that specifies the module it should override the dependency from. So if MainActivity has an injected sharedPreferences, and we are testing MainActivity:

@RunWith(InjectorAndroidRobolectricGradleTestRunner.class)
public class MainActivityTest {
    @InjectOverride(module = TestAndroidModule.class)
    SharedPreferences sharedPreferences; // note that this shouldn't be assigned a value; it will be set by the framework
}

When Robolectric runs MainActivity, its sharedPreferences instance will be the same as the instance in our test class, so it can be stubbed, verified, etc...

To add a new test module, create a new class in test/java/com/staticbloc/injector/android/injection/modules and extend the Module that you want to test. It should also implement OverridableModule (so we can use OverrideInject with it). It's constructor should take whatever parameters need to passed to the super-Module, as well as an instance of TestApplicationInjectorImpl. Any @Provides method should call TestApplicationInjectorImpl.hasOverridingBinding to check if there is an override in place for this return type. Here's what TestAndroidModule looks like:

@Module
public class TestAndroidModule extends AndroidModule implements OverridableModule {
  private final TestApplicationInjectorImpl testApplicationInjector;

  public TestAndroidModule(InjectorAndroidApp application, TestApplicationInjectorImpl testApplicationInjector) {
    super(application);

    this.testApplicationInjector = testApplicationInjector;
  }

  @Override @Provides @PerApp LocationManager provideLocationManager() {
    if(testApplicationInjector.hasOverridingBinding(getClass(), LocationManager.class)) {
      return testApplicationInjector.getOverridingBinding(getClass(), LocationManager.class);
    }
    return mock(LocationManager.class);
  }

  @Override @Provides @PerApp SharedPreferences provideSharedPreferences() {
    if(testApplicationInjector.hasOverridingBinding(getClass(), SharedPreferences.class)) {
      return testApplicationInjector.getOverridingBinding(getClass(), SharedPreferences.class);
    }
    return mock(SharedPreferences.class);
  }
}

The test Injectors follow the same principles as the regular ones. Just make sure to remember to use test Modules when creating the components!

• Unit Tests

  1. Open the Run Configurations window
  2. From the configuration window on the left, under Defaults, select JUnit
  3. Test kind: All in package
  4. Package:
  5. Search for tests: In single module
  6. VM options: -ea -Xmx2048m
  7. Working directory: app
  8. Use classpath of module: app
  9. Before launch
  10. Gradle-aware Make (a popup window will ask for a task; just leave it blank)
  11. Apply your changes
  12. Create new JUnit configuration (+ -> JUnit)
      • Name: runall
      • Everything else should be the JUnit defaults you set up in the previous steps

• Integration Tests

  1. Nothing yet (PRs are welcome)