Part 12 – Subcomponents


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In part 12 of the Dagger 2 tutorial, we will learn how to use Subcomponents, which are an alternative to component dependencies for connecting multiple components and applying different scopes.
A Subcomponent is generated as a non-static inner class of its parent component and this way can access its whole object graph.

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Links & DependenciesExampleApp.javaAndroidManifest.xmlPerActivity.javaAppComponent.javaDriverModule.javaDriver.javaPetrolEngine.javaDieselEngine.javaPetrolEngineModule.javaDieselEngineModule.javaRims.javaTires.javaWheelsModule.javaRemote.javaCar.javaEngine.javaWheels.javaMainActivity.javaActivityComponent.java

Dagger 2 dependencies:

github.com/google/dagger

package com.codinginflow.dagger2example;

import android.app.Application;

import com.codinginflow.dagger2example.dagger.AppComponent;
import com.codinginflow.dagger2example.dagger.DaggerAppComponent;

public class ExampleApp extends Application {
    private AppComponent component;

    @Override
    public void onCreate() {
        super.onCreate();

        component = DaggerAppComponent.create();
    }

    public AppComponent getAppComponent() {
        return component;
    }
}
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.dagger2example">

    <application
        android:name=".ExampleApp"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>
package com.codinginflow.dagger2example.dagger;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;

import javax.inject.Scope;

import static java.lang.annotation.RetentionPolicy.RUNTIME;

@Scope
@Documented
@Retention(RUNTIME)
public @interface PerActivity {
}
package com.codinginflow.dagger2example.dagger;

import javax.inject.Singleton;

import dagger.Component;

@Singleton
@Component(modules = DriverModule.class)
public interface AppComponent {

    ActivityComponent getActivityComponent(DieselEngineModule dieselEngineModule);
}
package com.codinginflow.dagger2example.dagger;

import com.codinginflow.dagger2example.car.Driver;

import javax.inject.Singleton;

import dagger.Module;
import dagger.Provides;

@Module
public abstract class DriverModule {

    @Provides
    @Singleton
    static Driver provideDriver() {
        return new Driver();
    }
}
package com.codinginflow.dagger2example.car;

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

import android.util.Log;

import javax.inject.Inject;
import javax.inject.Named;

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

    private int horsePower;
    private int engineCapacity;

    @Inject
    public PetrolEngine(@Named("horse power") int horsePower,
                        @Named("engine capacity") int engineCapacity) {
        this.horsePower = horsePower;
        this.engineCapacity = engineCapacity;
    }

    @Override
    public void start() {
        Log.d(TAG, "Petrol engine started. " +
                "\nHorsepower: " + horsePower +
                "\nEngine capacity: " + engineCapacity);
    }
}
package com.codinginflow.dagger2example.car;

import android.util.Log;

import javax.inject.Inject;

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

    private int horsePower;

    @Inject
    public DieselEngine(int horsePower) {
        this.horsePower = horsePower;
    }

    @Override
    public void start() {
        Log.d(TAG, "Diesel engine started. Horsepower: " + horsePower);
    }
}
package com.codinginflow.dagger2example.dagger;

import com.codinginflow.dagger2example.car.Engine;
import com.codinginflow.dagger2example.car.PetrolEngine;

import dagger.Binds;
import dagger.Module;

@Module
public abstract class PetrolEngineModule {

    @Binds
    abstract Engine bindEngine(PetrolEngine engine);
}
package com.codinginflow.dagger2example.dagger;

import com.codinginflow.dagger2example.car.DieselEngine;
import com.codinginflow.dagger2example.car.Engine;

import dagger.Module;
import dagger.Provides;

@Module
public class DieselEngineModule {
    private int horsePower;

    public DieselEngineModule(int horsePower) {
        this.horsePower = horsePower;
    }

    @Provides
    int provideHorsePower() {
        return horsePower;
    }

    @Provides
    Engine provideEngine(DieselEngine engine) {
        return engine;
    }
}
package com.codinginflow.dagger2example.car;

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

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.dagger;

import com.codinginflow.dagger2example.car.Rims;
import com.codinginflow.dagger2example.car.Tires;
import com.codinginflow.dagger2example.car.Wheels;

import dagger.Module;
import dagger.Provides;

@Module
public abstract 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.car;

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.car;

import android.util.Log;

import com.codinginflow.dagger2example.dagger.PerActivity;

import javax.inject.Inject;

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

    private Driver driver;
    private Engine engine;
    private Wheels wheels;

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

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

    public void drive() {
        engine.start();
        Log.d(TAG, driver + " drives " + this);
    }
}
package com.codinginflow.dagger2example.car;

public interface Engine {

    void start();
}
package com.codinginflow.dagger2example.car;

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 com.codinginflow.dagger2example.car.Car;
import com.codinginflow.dagger2example.dagger.ActivityComponent;
import com.codinginflow.dagger2example.dagger.DieselEngineModule;

import javax.inject.Inject;

public class MainActivity extends AppCompatActivity {
    @Inject Car car1, car2;

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

        ActivityComponent component = ((ExampleApp) getApplication()).getAppComponent()
                .getActivityComponent(new DieselEngineModule(120));

        component.inject(this);

        car1.drive();
        car2.drive();
    }
}
package com.codinginflow.dagger2example.dagger;

import com.codinginflow.dagger2example.MainActivity;
import com.codinginflow.dagger2example.car.Car;

import javax.inject.Named;

import dagger.BindsInstance;
import dagger.Component;
import dagger.Subcomponent;

@PerActivity
@Subcomponent(modules = {WheelsModule.class, DieselEngineModule.class})
public interface ActivityComponent {

    Car getCar();

    void inject(MainActivity mainActivity);


    /*@Component.Builder
    interface Builder {

        @BindsInstance
        Builder horsePower(@Named("horse power") int horsePower);

        @BindsInstance
        Builder engineCapacity(@Named("engine capacity") int engineCapacity);

        Builder appComponent(AppComponent component);

        ActivityComponent build();
    }*/
}