The document discusses Clean Architecture and provides an example of implementing it using a Movie Night app. It describes separating the app into Presentation, Data, and Domain layers with specific responsibilities. The Domain layer contains entities, use cases, and interfaces. The Data layer encapsulates data sources and mappers. The Presentation layer connects everything using ViewModels, LiveData, and observing lifecycle changes. It demonstrates how data flows from the Data layer through UseCases to the Presentation layer and updates the UI.

1. Clean Architecture:
A Guided Tour
Yossi Segev
Tech Lead @ Kin Ecosystem
@yossisegev
yossisegev.com

2. Clean Architecture:
A Guided Tour
Yossi Segev
Tech Lead @ Kin Ecosystem
@yossisegev
yossisegev.com

3. Why are we obsessed
with architecture?

4. We want to be able to
REACT TO CHANGES
quickly & efficiently

5. Good architecture is
•Easy to maintain / expand upon
•Easy to test
•Easy to understand

6. Keep in mind
•Architecture is dynamic and ever-evolving
•There are always several solutions to every problem
•Every architecture decision is a trade-off
•There is no such thing as “the perfect
architecture”

7. Clean Architecture

8. The Layers Principle
Layer C
Layer B
Layer A
DependenciesFlow
<< Detailed
<< Generic

9. Movie Night app layers
Presentation
Data
Domain
DependenciesFlow

10. Movie Night app layers
Presentation
Data
Domain
•UI
•Presenters
•Dependency Injection
•Web API
•Storage (DB/In-Mem)
•Use cases
•Interfaces
•Domain Entities
DependenciesFlow

11. Modules as layers
*Not by dependency flow order

12. build.gradle
dependencies {
implementation project(':domain')
// ...
}

13. Movie Night app layers
Presentation
Data
Domain
•UI
•Presenters
•Dependency Injection
•Web API
•Storage (DB/In-Mem)
•Use cases
•Interfaces
•Domain Entities
DependenciesFlow

14. The Domain Layer
•The baseline of the application
•Describes what the application is / what it can do
•Generic code

15. • Domain Entities
• Use cases
• Interfaces
The Domain Layer

16. Domain Entities
• Simple data containers
• The basic building blocks of our application
• Acts as common language across the
application

17. MovieNight’s
Domain Entities

18. MovieEntity.kt
data class MovieEntity(
var id: Int = 0,
var title: String,
var overview: String? = null,
var voteCount: Int = 0
// ...
)

19. • Domain Entities
• Use cases
• Interfaces
The Domain Layer

20. Use Case
Encapsulates a single,
very specific task
to be performed

21. MovieNight’s Use Cases

22. UseCase.kt
abstract class UseCase<T>() {
abstract fun create(): Observable<T>
fun observable(): Observable<T> {
return create().compose(t)
}
}

23. UseCase.kt
abstract class UseCase<T>() {
abstract fun create(): Observable<T>
fun observable(): Observable<T> {
return create().compose(t)
}
}

24. UseCase.kt
abstract class UseCase<T>(t: ObservableTransformer) {
abstract fun create(): Observable<T>
fun observable(): Observable<T> {
return create().compose(t)
}
}

25. UseCase.kt
abstract class UseCase<T>(t: ObservableTransformer) {
abstract fun create(): Observable<T>
fun observable(): Observable<T> {
return create().compose(t)
}
}

26. UseCase.kt
abstract class UseCase<T>(t: ObservableTransformer) {
abstract fun create(): Observable<T>
fun observable(): Observable<T> {
return create().compose(t)
}
}

27. Using a UseCase

28. Using a UseCase
myUseCase
.observable()
.subscribe(
{ data ->
// Do something with the data
},
{ throwable ->
// Handle errors
}
)

29. Using a UseCase
myUseCase
.observable()
.subscribe(
{ data ->
// Do something with the data
},
{ throwable ->
// Handle errors
}
)

30. Using a UseCase
myUseCase
.observable()
.subscribe(
{ data ->
// Do something with the data
},
{ throwable ->
// Handle errors
}
)

31. Using a UseCase
myUseCase
.observable()
.subscribe(
{ data ->
// Do something with the data
},
{ throwable ->
// Handle errors
}
)

32. GetPopularMovies
UseCase

33. GetPopularMovies.kt
class GetPopularMovies(t: Transformer,
repo: MoviesRepo)
:UseCase<List<MovieEntity>>(t) {
override fun create(): Observable<List<MovieEntity>> {
return repo.getMovies()
}
}

34. GetPopularMovies.kt
class GetPopularMovies(t: Transformer,
repo: MoviesRepo)
:UseCase<List<MovieEntity>>(t) {
override fun create(): Observable<List<MovieEntity>> {
return repo.getMovies()
}
}

35. GetPopularMovies.kt
class GetPopularMovies(t: Transformer,
repo: MoviesRepo)
:UseCase<List<MovieEntity>>(t) {
override fun create(): Observable<List<MovieEntity>> {
return repo.getMovies()
}
}

36. MoviesRepo.kt
interface MoviesRepo {
fun getMovies(): Observable<List<MovieEntity>>
// . . .
}

37. • Domain Entities
• Use cases
• Interfaces
The Domain Layer

38. Interfaces
• Dictates the contract the upper layers must
follow
• Ensures the application core functionality will
hold true, regardless implementation details
changes

39. Moving up!

40. The Data Layer

41. Movie Night app layers
Data
Domain
•Web API
•Storage (DB/In-Mem)
•Domain Entities
•Interfaces
•Use cases

42. The Data Layer
•Caching mechanism
•Database
•Networking
•Mappers

43. The Data Layer
Encapsulates any knowledge regarding where the
application data is coming from and how it is stored

44. In-Mem
StorageAPIDB
Data Layer
Application

45. The Data Layer
•Caching mechanism
•Database
•Networking
•Mappers

46. Mappers
Maps Class A to Class B

47. Mapper.kt
abstract class Mapper<in E, T> {
abstract fun mapFrom(from: E): T
// ...
}

48. MyMapper.kt
class MyMapper: Mapper<MovieEntity, MovieData>() {
override fun mapFrom(from: MovieEntity): MovieData {
return MovieData(
id = from.id,
originalTitle = from.originalTitle,
releaseDate = from.releaseDate,
overview = from.overview
// ...
)
}
}

49. MyMapper.kt
class MyMapper: Mapper<MovieEntity, MovieData>() {
override fun mapFrom(from: MovieEntity): MovieData {
return MovieData(
id = from.id,
originalTitle = from.originalTitle,
releaseDate = from.releaseDate,
overview = from.overview
// ...
)
}
}

50. MyMapper.kt
class MyMapper: Mapper<MovieEntity, MovieData>() {
override fun mapFrom(from: MovieEntity): MovieData {
return MovieData(
id = from.id,
originalTitle = from.originalTitle,
releaseDate = from.releaseDate,
overview = from.overview
// ...
)
}
}

51. Why do we need Mappers?

52. import android.arch.persistence.room.Entity
import android.arch.persistence.room.PrimaryKey
import com.google.gson.annotations.SerializedName
@Entity(tableName = "movies")
data class MovieData(
@PrimaryKey
var id: Int = -1,
@SerializedName("original_title")
var originalTitle: String
// ...
)
MovieData.kt

53. Why do we need Mappers?
The Data layer contains details
we want to hide.

54. Data Layer
Mapper
DBApplication
Mapper

55. Data Layer
Mapper
DBApplication
Mapper

56. Data Layer
Mapper
DBApplication
Mapper

57. Data Layer
Mapper
DBApplication
Mapper

58. Data Layer
Mapper
DBApplication
Mapper

59. Summarising the
Data Layer
•Contains concrete implementations of data providers
•Act as a boundary, encapsulates data providers details
and hide them from the “outside world”.

60. Movie Night app layers
Presentation
Data
Domain
•UI
•Presenters
•Dependency Injection
•Web API
•Storage (DB/In-Mem)
•Use cases
•Interfaces
•Domain Entities
DependenciesFlow

61. The Presentation Layer

62. The Presentation Layer
Connects all the different pieces into a
single, functioning unit that is the
application

63. The Presentation Layer
•Activities, Fragments
•View States
•Presenters
•Mappers
•Dependency Injection

64. Presentation Layer
Architecture
Fragment
ViewModel
LiveData
Use Case
Notify
Observes

65. Why ViewModel & LiveData?
Lifecycle awareness.

66. ViewModel 101
class MainActivity : AppCompatActivity() {
val vm = ViewModelProviders
.of(lifecycleOwner)
.get(MyViewModel::class.java)
}

67. ViewModel 101
class MainActivity : AppCompatActivity() {
// Creation
val vm = ViewModelProviders
.of(lifecycleOwner)
.get(MyViewModel::class.java)
}

68. ViewModel 101
class MainActivity : AppCompatActivity() {
// Creation
val vm = ViewModelProviders
.of(lifecycleOwner)
.get(MyViewModel::class.java)
}

69. ViewModel 101
class MainActivity : AppCompatActivity() {
// Creation
val vm = ViewModelProviders
.of(lifecycleOwner)
.get(MyViewModel::class.java)
}

70. ViewModel 101
class MyViewModel: ViewModel() {
// ...
override fun onCleared() {
super.onCleared()
// Clear resources etc...
}
}

71. LiveData 101

72. LiveData 101
// Creating
val liveData = MutableLiveData<String>()
// Observing
liveData.observe(lifecycleOwner, Observer { data ->
// do something with data…
})
// Updating value
liveData.value = "Hello world!"

73. LiveData 101
// Creating
val liveData = MutableLiveData<String>()
// Observing
liveData.observe(lifecycleOwner, Observer { data ->
// do something with data…
})
// Updating value
liveData.value = "Hello world!"

74. LiveData 101
// Creating
val liveData = MutableLiveData<String>()
// Observing
liveData.observe(lifecycleOwner, Observer { data ->
// do something with data…
})
// Updating value
liveData.value = "Hello world!"

75. Fragment
ViewModel
LiveData
Presentation Layer
Architecture
Use Case
Notify
Observes

76. The Presentation Layer
•Activities, Fragments
•View States
•Presenters
•Mappers
•Dependency Injection

77. ViewModel
LiveData
Presentation Layer
Architecture
Fragment
Observes
Use Case
Notify

78. ViewState
Represents the state of a view

79. PopularViewState.kt
data class PopularViewState(
var loading: Boolean = true,
var movies: List<MovieEntity>? = null
)

80. ViewModel
LiveData
Presentation Layer
Architecture
Fragment
Subscribes
Use Case
Notify

81. ViewModel
LiveData
Presentation Layer
Architecture
Fragment
Subscribes
Use Case
Notify

82. PopularViewModel

83. class PopularViewModel(val useCase: GetPopularMovies)
: BaseViewModel() {
var viewState: MutableLiveData<PopularViewState>
init {
viewState.value = PopularViewState()
}
PopularViewModel.kt

84. class PopularViewModel(val useCase: GetPopularMovies)
: BaseViewModel() {
var viewState: MutableLiveData<PopularViewState>
init {
viewState.value = PopularViewState()
}
PopularViewModel.kt

85. class PopularViewModel(val useCase: GetPopularMovies)
: BaseViewModel() {
var viewState: MutableLiveData<PopularViewState>
init {
// Sets the initial view state
viewState.value = PopularViewState()
}
// ...
PopularViewModel.kt

86. getPopularMovies
.observable()
.subscribe({ movies ->
val newState = viewState.value
.copy(loading = false,
movies = movies)
this.viewState.value = newState
}, { throwable ->
// Handle errors
}))
PopularViewModel.kt

87. getPopularMovies
.observable()
.subscribe({ movies ->
}, { throwable ->
// Handle errors
}))
PopularViewModel.kt

88. getPopularMovies
.observable()
.subscribe({ movies ->
val newState = viewState.value
.copy(loading = false,
movies = movies)
}, { throwable ->
// Handle errors
}))
PopularViewModel.kt

89. getPopularMovies
.observable()
.subscribe({ movies ->
val newState = viewState.value
.copy(loading = false,
movies = movies)
viewState.value = newState
}, { throwable ->
// Handle errors
}))
PopularViewModel.kt

90. PopularViewModel.kt
val disposable = getPopularMovies
.observable()
.subscribe( /* ... */ )
addDisposable(disposable)

91. ViewModel
LiveData
Presentation Layer
Architecture
Fragment
Subscribes
Use Case
Notify

92. ViewModel
LiveData
Presentation Layer
Architecture
Fragment
Subscribes
Use Case
Notify

93. PopularMoviesFragment.kt
val viewModel = ViewModelProviders
.of(this, factory)
.get(PopularViewModel::class.java)
// ...
viewModel.viewState
.observe(this, Observer { state ->
handleViewState(state)
})

94. PopularMoviesFragment.kt
val viewModel = ViewModelProviders
.of(this, factory)
.get(PopularViewModel::class.java)
// ...
viewModel.viewState
.observe(this, Observer { state ->
handleViewState(state)
})

95. PopularMoviesFragment.kt
fun handleViewState(state: PopularViewState) {
if (state.loading) {
// Show or hide the progressBar
}
state.movies?.let {
// Show movies
}
}

96. The Presentation Layer
•Activities, Fragments
•View States
•Presenters
•Mappers
•Dependency Injection

97. Dependency Injection
• Wires everything across the application
• Providing concrete implementations

98. Summary

99. Thank you
https://github.com/mrsegev/MovieNight