Part 5 – Module & Provider Methods


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In part 5 of the Dagger 2 tutorial, we will learn how to use modules and provider methods to add objects to the dependency graph that can’t use an @Inject constructor, like classes that belong to 3rd party libraries.
Modules are simple Java classes that we annotate with @Module and add to a component. They contain methods that are annotated with @Provides and which define how objects get instantiated and configured. These provider methods can have their very own dependencies as arguments, which Dagger will then provide if possible. By making provider methods static, we can get a performance boost because our component doesn’t have to instantiate the module to call them.

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Links & DependenciesRims.javaTires.javaWheelsModule.javaRemote.javaCar.javaEngine.javaWheels.javaMainActivity.javaCarComponent.java

Dagger 2 dependencies:

github.com/google/dagger

package com.codinginflow.dagger2example;

public class Rims {
    //we don't own this class so we can't annotate it with @Inject
}
package com.codinginflow.dagger2example;

import android.util.Log;

public class Tires {
    //we don't own this class so we can't annotate it with @Inject

    private static final String TAG = "Car";

    public void inflate() {
        Log.d(TAG, "Tires inflated");
    }
}
package com.codinginflow.dagger2example;

import dagger.Module;
import dagger.Provides;

@Module
public class WheelsModule {

    @Provides
    static Rims provideRims() {
        return new Rims();
    }

    @Provides
    static Tires provideTires() {
        Tires tires = new Tires();
        tires.inflate();
        return tires;
    }

    @Provides
    static Wheels provideWheels(Rims rims, Tires tires) {
        return new Wheels(rims, tires);
    }
}
package com.codinginflow.dagger2example;

import android.util.Log;

import javax.inject.Inject;

public class Remote {
    private static final String TAG = "Car";

    @Inject
    public Remote() {

    }

    public void setListener(Car car) {
        Log.d(TAG, "Remote connected");
    }
}
package com.codinginflow.dagger2example;

import android.util.Log;

import javax.inject.Inject;

public class Car {
    private static final String TAG = "Car";

    private Engine engine;
    private Wheels wheels;

    @Inject
    public Car(Engine engine, Wheels wheels) {
        this.engine = engine;
        this.wheels = wheels;
    }

    @Inject
    public void enableRemote(Remote remote) {
        remote.setListener(this);
    }

    public void drive() {
        Log.d(TAG, "driving...");
    }
}
package com.codinginflow.dagger2example;

import javax.inject.Inject;

public class Engine {

    @Inject
    public Engine() {

    }
}
package com.codinginflow.dagger2example;

public class Wheels {
    //we don't own this class so we can't annotate it with @Inject

    private Rims rims;
    private Tires tires;

    public Wheels(Rims rims, Tires tires) {
        this.rims = rims;
        this.tires = tires;
    }
}
package com.codinginflow.dagger2example;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import javax.inject.Inject;

public class MainActivity extends AppCompatActivity {
    @Inject Car car;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        CarComponent component = DaggerCarComponent.create();
        component.inject(this);

        car.drive();
    }
}
package com.codinginflow.dagger2example;

import dagger.Component;

@Component(modules = WheelsModule.class)
public interface CarComponent {

    Car getCar();

    void inject(MainActivity mainActivity);
}