Interface + Gradle Build Variants

When I’m working on a regional mobile app recently, I start to notice an useful usage of interface when combine with Gradle Build Variants in Android Studio.

Firstly, I put an interface in the main project.

public interface CurrencyFormatUtil {
    String formatMoney(double number);
}

Then I add the Impl class in both HongKong & Malaysia build variants with different implementation.

public class HongKongCurrencyFormatUtil implements CurrencyFormatUtil {
    private static final String CURRENCY_SYMBOL = "HK$";

    @Inject public HongKongCurrencyFormatUtil() {
    }

    @Override public String formatMoney(double number) {
        return "HK$ 1.8 M";
    }
}

public class MalaysiaCurrencyFormatUtil implements CurrencyFormatUtil {
    private static final String CURRENCY_SYMBOL = "RM";

    @Inject public MalaysiaCurrencyFormatUtil() {
    }

    @Override public String formatMoney(double number) {
        return "RM 1,800,000";
    }
}

With a little help from Google Dagger 2 dependency injection library, it will be able to return different currency format implementation base on build variant selection.

@Module
public class HongKongDaggerModule {
    @Provides CurrencyFormatUtil provideCurrencyFormatUtil() {
        return new HongKongCurrencyFormatUtil();
    }
}

@Module
public class MalaysiaDaggerModule {
    @Provides CurrencyFormatUtil provideCurrencyFormatUtil() {
        return new MalaysiaCurrencyFormatUtil();
    }
}

Lastly, I just need to inject it in the main project.

public class MainActivity extends AppCompatActivity {
    @Inject CurrencyFormatUtil currencyFormatUtil;

    private void showContent() {
        textView.setText(currencyFormatUtil.formatMoney(1800000.0));
    }
}

That’s it.