What is the specific requirement to use Dagger2 in any android application? What are the actual benefits of using dagger2 in an android application?

Question

I read the dagger 2 documentation but still not able to find that in what condition I should use dagger2 in my application and what are the benefits of its implementation?

It's a dependency injection framework. So it's useful whenever you need to use dependency injection. Which is whenever you need to call a method in your code that belongs to another class. Which is pretty much always? I like this article https://spring.io/blog/2011/08/26/clean-code-in-android-applications just replace Guice with Dagger — EpicPandaForce, Feb 11 '17 at 18:40
Possible duplicate of [Beside testing, why do we need Dagger 2?](http://stackoverflow.com/questions/41895802/beside-testing-why-do-we-need-dagger-2) — David Rawson, Feb 11 '17 at 22:27

score 0 · Accepted Answer · edited May 23 '17 at 11:53

1.) to use Dagger2, you need to include it as a dependency in your project.

annotationProcessor 'com.google.dagger:dagger-compiler:2.9'
compile 'com.google.dagger:dagger:2.9'
provided 'org.glassfish:javax.annotation:10.0-b28'

Then you can use Dagger2.

2.) Whenever you have a class which is the dependency of another class.

So if you have something like this:

public int getNewRandomNumber() {
    return new Random().nextInt(5000);
}

Then you have an implicit dependency on Random and it is not mockable.

So you might want to provide this as a dependency to the method instead:

public int getNewRandomNumber(Random random) {
   return random.nextInt(5000);
}

But you might be using Random in a bunch of places, so you might want to provide it to the class itself:

public class RandomGenerator {
    private final Random random;

    public RandomGenerator(Random random) {
        this.random = random;
    }
}

After which the question surfaces: if you need an instance of RandomGenerator, where are you getting Random from?

Surely this is stupid:

RandomGenerator gen = new RandomGenerator(new Random());

Wouldn't it be nicer to do either this:

RandomGenerator randomGenerator = component.randomGenerator();

or

@Inject
RandomGenerator randomGenerator;

Well apparently with Dagger it's pretty easy

@Module
public class RandomModule {
    @Provides
    @Singleton
    Random random() {
        return new Random();
    }
}

@Singleton
@Component(modules={RandomModule.class})
public interface SingletonComponent {
    Random random();
    RandomGenerator randomGenerator();
}

then

@Singleton
public class RandomGenerator {
    private final Random random;

    @Inject
    public RandomGenerator(Random random) {
        this.random = random;
    }
}

or

@Singleton
public class RandomGenerator {
    @Inject
    Random random;

    @Inject
    public RandomGenerator() {
    }
}

You can read more about dependency injection here

What is the specific requirement to use Dagger2 in any android application? What are the actual benefits of using dagger2 in an android application?

1 Answers1