Architect android apps with MVP, Dagger, Retrofit, Gson, JSON, Kotlin Data Classes and RecyclerView using Kotlin. How to Convert JSON to Kotlin Data Classes. Kotlin Retrofit Example with RecyclerView. MVP Android using Kotlin project structure. Kotlin Android Dagger2 Tutorial. How to use GSON serialization for JSON response in Kotlin. Find More on: http://developine.com/building-android-mvp-app-in-kotlin-using-dagger-retrofit/ And http://developine.com/

1. ARCHITECT ANDROID APPS
WITH MVP, DAGGER,
RETROFIT USING KOTLIN
PRESENTED BY: DEVELOPINE.COM

2. CONTENTS
KOTLIN
ANDROID MVP
RETROFIT 2
DAGGER 2
JSON/GSON MAPPING - KOTLIN DATA
CLASSS
RECYCLERVIEW ADAPTER KOTLIN

3. WE WILL COVER ALL CONTENTS
IN THIS SEQUENCE-1
W h y u s e M V P D e s i g n P a t t e r n i n A n d r o i d .
H o w t o s t r u c t u r e A n d r o i d p r o j e c t f o r
i m p l e m e n t i n g M V P i n A n d r o i d a p p s u s i n g K o t l i n .
W h y w e n e e d D e p e n d e n c y I n j e c t i o n ( D I ) i n
A n d r o i d .
I n t r o t o D a g g e r 2 ( D I ) l i b r a r y i n A n d r o i d .

4. WE WILL COVER ALL CONTENTS
IN THIS SEQUENCE-2
S e t u p D a g g e r a n d R e t r o f i t G r a d l e d e p e n d e n c i e s .
I m p l e m e n t i n g D a g g e r 2 i n A n d r o i d u s i n g K o t l i n .
I m p l e m e n t i n g R e t r o f i t i n A n d r o i d u s i n g K o t l i n .
I m p l e m e n t i n g R e c y c l e r V i e w i n K o t l i n .

5. WWW.DEVELOPINE.COM
O R I G I N A L F U L L A R T I C L E C A N A L S O B E F O U N D O N
O U R B L O G :
h t t p : / / d e v e l o p i n e . c o m / b u i l d i n g - a n d r o i d - m v p - a p p - i n -
k o t l i n - u s i n g - d a g g e r - r e t r o f i t /

6. WHY NEED MVP DESIGN
PATTERN IN ANDROID
MVP (MODEL-VIEW-PRESENTER) in Android is used
to manage code in an efficient way.
MVP in Android facilitate separation of concern
and help to implement unit tests in Android
without Views.

7. THE MODEL LAYER
The Model layer is used to provide data to the
presenter, so presenter can pass it to view layer
for displaying data on UI.
Only Presenter can interact with Model, View
cannot directly communicate with Model.
Model is usually a Data Manager. It has to decide
or act to get data from API (Network), Shared
Preferences or SQlite database.

8. THE VIEW LAYER
Any Java or Kotlin class in Android app which can
make changes in UI comes under View.
Activities/Fragments/ Adapters/ Custom Views
are all Views in Kotlin.
Any user interaction on View layer e.g Button
click should be passed to the presenter.
The presenter will decide what action to
perfrom.

9. THE PRESENTER LAYER
The presenter is the middle man between view
and model.
View will only interact with presenter by calling
its functions.
Presenter is responsible to get data, perform any
operation on data like JSON parsing / cache data
and inform/update View by callings its functions

10. PROJECT PACKAGES
STRUCTURE FOR IMPLEMENTING
MVP AND DAGGER IN ANDROID-1
<< Create following packages in your Android App. >>
data- (Add POJO/ DATA CLASSES in this package)
network- (Add API EndPoints , Retrofit Request Response
Interface in this package)
utils- (any utility classes or functions)

11. PROJECT PACKAGES
STRUCTURE FOR IMPLEMENTING
MVP AND DAGGER IN ANDROID-2
<< Create following packages in your Android App. >>
ui (Activities/Fragments)
service (Any service classes e.g Push Notification Handling)
di (Dependency Injection / Dagger2 Code will go here)

12. IMPLEMENTING MVP IN ANDROID
USING KOTLIN-1
We will Create new Activity PostActivity.kt in our Android
project inside ui package.
Which will make API call using Retrofit and show JSON
Response in RecyclerView using Kotlin.
PostActivity.kt is our View.
I will show you how View interacts with Model and Presenter
in MVP (Model-View-Presenter).

13. IMPLEMENTING MVP IN ANDROID
USING KOTLIN-2
Create PostView.kt Interface.
Create PostPresenter.kt Interface.
Create Presenter Implementation class PostPresenterImpl.kt
PostPresenterImpl.kt will implement interface
PostPresesnter.kt

14. IMPLEMENTING MVP IN ANDROID
USING KOTLIN-3
PostActivity.kt will have reference to the
PostPresenterImpl.kt class.
PostActivity.kt will implement PostView.kt

15. VIEW INTERFACE POSTVIEW.KT
//Presenter will call this method after getting list of posts from API.
// And will pass it List of Posts for displaying in RecyclerView.
interface PostView {
fun showAllPosts(postList: List<PostData>)
}

16. PRESENTER INTERFACE
POSTPRESENTER.KT
- View will call this method from presenter.
- This method will load all posts from API using Retrofit2 and will send
response to the View by callings its method showAllPosts(lists) and will
pass list of posts for populating in RecyclerView using Kotlin.
interface PostPresenter {
fun getAllPosts()
}

17. POSTACTIVITY.KT
class PostActivity : AppCompatActivity(), PostView {
lateinit var postPresenter: PostPresenter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_post)
postPresenter = PostPresenterImpl(this, application)
postPresenter.getAllPosts()
}
override fun showAllPosts(postList: List<PostData>) {
// showing this postList in RecyclerView code will be here.
rv_post_list.layoutManager = LinearLayoutManager(this)
rv_post_list.adapter = PostItemAdapter(postList, this)
} }

18. POSTACTIVITY.KT LAYOUT FILE
ACTIVITY_POST.XML
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.es.developine.ui.posts.PostActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/rv_post_list"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>

19. POST PRESENTER
IMPLEMENTATION CLASS-1
PostPresenterImpl.kt is responsible to make API call.
Fetch list of posts using Retrofit Network Client.
Return list of posts to the PostActivity.kt. so PostActivity.kt
can display posts in RecyclerView using Kotlin.
I will be using dagger2 annotations in this class. we will
shortly cover Dependency Injection using Dagger2 in kotlin.

20. POST PRESENTER
IMPLEMENTATION CLASS-2
class PostPresenterImpl(var postView: PostView, var applicationComponent:
Application) : PostPresenter {
@Inject
lateinit var mNetworkApi: INetworkApi
init {
(applicationComponent as ApplicationClass).applicationComponent.inject(this)
}
override fun getAllPosts() {
var allPosts = mNetworkApi.getAllPosts()
allPosts.subscribeOn(IoScheduler()).observeOn(AndroidSchedulers.mainThread())
.subscribe {
postView.showAllPosts(it)
}
}
}

21. LETS FIRST SETUP GRADLE
DEPENDENCIES FOR RETROFIT-2,
DAGGER-2 AND RECYCLERVIEW
dependencies {
implementation 'com.android.support:recyclerview-v7:27.1.1'
//retrofit_version = '2.4.0'
implementation "com.squareup.retrofit2:retrofit:$retrofit_version"
implementation "com.squareup.retrofit2:converter-gson:$retrofit_version"
implementation "com.squareup.retrofit2:adapter-rxjava2:$retrofit_version"
implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'
implementation 'com.google.dagger:dagger-android:2.15'
implementation 'com.google.dagger:dagger-android-support:2.15'
// if you use the support libraries
kapt 'com.google.dagger:dagger-android-processor:2.15'
kapt 'com.google.dagger:dagger-compiler:2.15'
}

22. WHY NEED DEPENDENCY
INJECTION (DI) - 1
- Dependency Injection (DI) is a design pattern in software engineering.
- It is a mechanism of providing required dependencies/objects to other classes
which need those dependencies.
For example, You have three classes in your project. ClassA, ClassB, ClassC.
ClassC needs an object of ClassA and ClassB.
Whereas ClassB needs an object of ClassA.

23. WHY NEED DEPENDENCY
INJECTION (DI) - 2
This means ClassC depends on ClassA and ClassB. And ClassB depends on
ClassA. (One class is dependent on another class / Dependency).
Now we don’t want to create objects of ClassA and ClassB inside ClassC. We
want to provide/pass initialized objects of ClassA and ClassB to ClassC.
For this purpose, we will inject (provide) required objects (dependencies) to
ClassC.
We will be using Dagger2 Android Library (using Kotlin language) for this
purpose.

24. INTRODUCTION TO DAGGER-2 IN
ANDROID
Dagger2 is a framework which is used to provide/manage
dependencies in Android/Java.
It uses annotations.
Annotations in Dagger2 (DI):
@Provides
@Module
@Component
@Inject

25. @PROVIDES ANNOTATION IN
DAGGER2 - 1
@Provides annotation is used with methods which provide
the certain dependency.
For example below function, provideRetrofit is annotated
with @Provides (which means it will provide a dependency of
type Retrofit object).

26. @PROVIDES ANNOTATION IN
DAGGER2 - 2
// Retrofit object is available for dependency injection.
@Provides
fun provideRetrofit(gson: Gson): Retrofit {
return
Retrofit.Builder().addConverterFactory(GsonConverterFactory.create(gson))
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.baseUrl("https://jsonplaceholder.typicode.com/").build()
}

27. @MODULE ANNOTATION IN
DAGGER2
- As mentioned earlier, We define methods in Module classes.
- We annotate module classes with @module annotation.
- And those methods provide the dependency.
A Module class is annotated with @Module annotation.
And it can provide an object/dependencies to the component class
throgu functions annotated with @Provides.

28. @COMPONENT ANNOTATION IN
DAGGER2 - 1
A component is an Interface which is annotated with @Component
annotation.
It has all modules from which it can get dependencies and provide
those dependencies where required.
A component knows from where it can get dependencies (from which
modules).
And where it has to provide dependencies.

29. @COMPONENT ANNOTATION IN
DAGGER2 - 1
// NetModule is class which is annotated with @Module annotation.
// NetModule class has functions annotated with @Provides (which return
dependency objects)
@Component(modules = [NetModule::class])
interface ApplicationComponent {
// this means ApplicationComponent has to provide/inject
// required dependencies in LoginPresenterImpl class.
fun inject(mLoginPresenterImpl: LoginPresenterImpl)
}

30. CONCLUSION
We have learned about MVP (Model-View-Presenter) in Android.
We have learned how to architect our Android apps to achieve MVP in
Android using Kotlin.
We have learned about Dagger2 in Android using Kotlin.
We have learned how to provide Retrofit Dependecies using Dagger2
in Android (Kotlin).
To Access full article on Android MVP Dagger Retrofit RecyclerView
using Kotlin visit:
http://developine.com/building-android-mvp-app-in-kotlin-using-dagger-
retrofit/