Android App From Scratch Part 2 — Implementing Must Have Libraries

In this tutorial series, I will try to create an RSS Reader app step by step. Through this series I will explain:

1. How to use Model-View-Presenter in an Android App
2. Implementing must have libraries
3. Implementing App Logic
4. Creating unit tests with JUnit
5. Creating Android Instrumentations tests with Espresso
6. Continuous Integration with Travis-CI

This article is the second part of a series.

Open source libraries make life easier. There are many awesome libraries we should use in our apps.

We will use these libraries:

• Dagger2
• Retrofit
• OkHttp Logging Interceptor
• RetrofitRssConverterFactory
• Leakcanary
• Picasso
• Chrome Custom Tabs

Dagger2

Dagger2 is a Dependency Injection library. I will implement it to this RSS Reader app. At first add these dependencies to app gradle file:

implementation "com.google.dagger:dagger:$dagger_version"
kapt "com.google.dagger:dagger-compiler:$dagger_version"
implementation "com.google.code.findbugs:jsr305:$findbugs_version"

Passing DaggerActivityComponent to ActivitiesBaseActivity.kt

abstract class BaseActivity : AppCompatActivity(), BaseView {

    /**
     * Layout resource to be inflated
     *
     * @return layout resource
     */
    @get:LayoutRes
    protected abstract val layoutResource: Int

    abstract fun inject(component: ActivityComponent)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(layoutResource)
        inject(DaggerActivityComponent.builder()
                .appComponent(NewsApp.component())
                .activityModule(ActivityModule(this))
                .build())
        init(savedInstanceState)
    }

    /**
     * Initializations
     */
    protected abstract fun init(state: Bundle?)

}

Now I create the presenter by injecting it. This approach is better than we did in part1. Each activity must implement the inject() method to make injections.

class MainActivity : BaseActivity(), MainContract.View {

    @Inject
    lateinit var mPresenter: MainContract.Presenter
    private lateinit var wrapper: ChromeTabsWrapper


    override val layoutResource = R.layout.activity_main

    override fun inject(component: ActivityComponent) {
        component.inject(this)
    }

    override fun init(state: Bundle?) {
        mPresenter.attach(this)
        mPresenter.loadHelloText()

        tvHello.setOnClickListener {
            mPresenter.loadHelloText()
        }
        wrapper = ChromeTabsWrapper(this)
    }

    override fun onTextLoaded(text: String) {
        tvHello.text = text
    }

    override fun onStart() {
        super.onStart()
        wrapper.bindCustomTabsService()
    }

    override fun onStop() {
        super.onStop()
        wrapper.unbindCustomTabsService()
    }

    override fun onDestroy() {
        super.onDestroy()
        mPresenter.detach()
    }


}

But the magic is here in DI Components and Modules:

@ActivityScope
@Component(dependencies = [AppComponent::class], modules = [ActivityModule::class])
interface ActivityComponent {

    fun mainPresenter(): MainContract.Presenter

    fun inject(mainActivity: MainActivity)
}

Module: Defining the injection

It is important that provideMainPresenter() method’s return type is MainContract.Presenter NOT MainPresenter We do abstraction by returning interface instead of the class.

@Module
class ActivityModule(private val activity: FragmentActivity) {

    @Provides
    @ActivityScope
    fun provideMainPresenter(service: RssService): MainContract.Presenter = MainPresenter(service)

}

Run the app. You can see that the behaviour is the same.

For more detailed explanation of Dagger2 you can see:

Understanding Dagger 2

Dependency Injection with Dagger 2 | CodePath Android Cliffnotes

Dagger ‡ A fast dependency injector for Android and Java.

Yet another MVP article — Part 1: Lets get to know the project

Retrofit

This awesome library is the most used Networking library. Retrofit is a type-safe Http client for Android and Java.

square/retrofit

OkHttp Logging Interceptor

Logger for OkHttp request/responses.

square/okhttp

RetrofitRssConverterFactory

A Retrofit 2 converter which parses Rss feeds. Optimized for RSS feed. Parses better than SimpleXmlConverterFactory.

faruktoptas/RetrofitRssConverterFactory

LeakCanary

A memory leak detection library for Android and Java.

“A small leak will sink a great ship.” — Benjamin Franklin

This is an awesome library for leak detection. Start using it when you build the project. If you make a mistake that leaks, you would find as early as possible.

debugCompile 'com.squareup.leakcanary:leakcanary-android:1.5'

In Application class:

public class RssApplication extends Application {


    @Override
    public void onCreate() {
        super.onCreate();
        LeakCanary.install(this);
    }

}

Picasso

Picasso is a great Image downloading and caching library. It has some alternatives. But we will use this.

compile 'com.squareup.picasso:picasso:2.5.2'

Chrome Custom Tabs

Chrome Custom Tabs give apps more control over their web experience, and make transitions between native and web content more seamless without having to resort to a WebView.

I will use this to browse RSS urls. I created a wrapper named ChromeTabsWrapper for Chrome Custom tabs operation. It is injected into MainActivity

private lateinit var wrapper: ChromeTabsWrapper
...
override fun onStart() {
    super.onStart()
    wrapper.bindCustomTabsService()
}

override fun onStop() {
    super.onStop()
    wrapper.unbindCustomTabsService()
}
...

Here is the source code for part2:

faruktoptas/news-mvp

You can go on reading with Part3

Android App From Scratch Part 3 — Implementing App Logic

Continue reading the next part?

Android App From Scratch Part 3 — Implementing App Logic

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