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Android Clean Architecture
BAU Mobile Application Fair
GDG
27th April 2018
Mohammed Touban
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ideatolife.me
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View
Activity
Web
Service
Activity Lifecycle
System Services
User Input
Dependency
Injection
Repository
Storage
Presenter
View
EditText
EditText
Button
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Clean Architecture
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“Elegance in design…
is a lack of unnecessary complexity”
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Clean Architecture
Separation of Concerns
Build layered applications with clear separation of responsibilities including view,
presentation, and domain logic.
State Synchronization
Synchronize data across screen state, session state, and server state.
Testability
Enables pure unit tests to test presentation logic and domain models in isolation.
Integration and UI tests for components that interact with the framework and/or display.
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visual representation of the Clean Architecture. All credit for this images goes to Uncle Bob
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“Those who do not remember the past
are condemned to repeat it.”
— George Santayana
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Clean Architecture
Separation of Concerns
Build layered applications with clear separation of responsibilities including view,
presentation, and domain logic.
State Synchronization
Synchronize data across screen state, session state, and server state.
Testability
Enables pure unit tests to test presentation logic and domain models in isolation.
Integration and UI tests for components that interact with the framework and/or display.
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Separation of Concerns
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View layer
Presentation model
Domain model
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Clean Architecture
Separation of Concerns
Build layered applications with clear separation of responsibilities including view,
presentation, and domain logic.
State Synchronization
Synchronize data across screen state, session state, and server state.
Testability
Enables pure unit tests to test presentation logic and domain models in isolation.
Integration and UI tests for components that interact with the framework and/or display.
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State Synchronization
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Screen state
Session state
Server state
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State Synchronization
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Screen state
Session state
Server state
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Clean Architecture
Separation of Concerns
Build layered applications with clear separation of responsibilities including view,
presentation, and domain logic.
State Synchronization
Synchronize data across screen state, session state, and server state.
Testability
Enables pure unit tests to test presentation logic and domain models in isolation.
Integration and UI tests for components that interact with the framework and/or display.
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T
estability
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Android framework dependencies encapsulated in view layer
Pure JVM unit tests for presenters and domain models
Espresso, Robolectric, or UI Automator tests for view layer
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Test Pyramid
- mike cohen book in 2009 “succeeding with agile”
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Android Test Pyramid
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Integration Tests
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Clean Architecture
Separation of Concerns
Build layered applications with clear separation of responsibilities including view,
presentation, and domain logic.
State Synchronization
Synchronize data across screen state, session state, and server state.
Testability
Enables pure unit tests to test presentation logic and domain models in isolation.
Integration and UI tests for components that interact with the framework and/or display.
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GUI Architectures
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GUI Architectures
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MVC
MVP
MVVM
MVI
MV…
…
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Supervising Controller (MVC)
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Smalltalk-80
One way flow of information
Controller handles user input and UI events
View observes changes in domain model
State Sync: Data Binding
Controller
Model
onLoginButtonClick()
setUser()
View
View.onClick()
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activity_login.xml
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Passive View (MVP)
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Also called Humble View
No dependency between view and domain model
Bi-directional flow of information
View replaced by fake in unit tests
State Sync: Flow Synchronization
View
View.onClick()
showUser()
Presenter
onLoginButtonClick()
Model
getUser()
View
showUser()
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class LoginPresenter(private val view: LoginView) { fun onLoginButtonClick(email:
String?, password: String?) {
if (email != null && password != null) {
val user = Model.getUser(email, password)
if (user != null) {
view.showUser(user)
} else {
view.showError(“Invalid credentials")
}
}
}
}
LoginPresenter.kt
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Presentation Model (MVVM)
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View forwards user input to presentation model
Presentation model mutates state using domain model
View observes changes in the presentation model
State Sync: Observer Pattern
ViewModel
Model
onLoginButtonClick()
getUser()
View
View.onClick()
onUpdateUser(
)
updateUser()
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Supervising
Controller
(MVC)
Passive
View
(MVP
)
Presentation
Model
(MVVM
)
Flow of Information One way Two way Two way
Model <> View
Dependency Yes No No
Sync Logic View Presenter View
State
Synchronization Data binding Flow synchronization Observer pattern
GUI Architectures
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Passive view migrates all sync logic into presentation layer
MVC and MVVM require sync logic in the view layer
For simpler apps, MVC or MVVM may be sufficient
MVP tests are more verbose and require a fake view
Humble View is the real MVP
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Android Passive View
Presenter
Activity
Presentation Logic
Model
Domain Logic
User Interface
User Input
Lifecycle Events
System Services
View
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Android Passive View
Presenter
Activity
Presentation Logic
Model
Domain Logic
View
User Interface
User Input
Lifecycle Events
System Services
View
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Android Passive View
Presenter
Activity
Presentation Logic
Controller
Model
Domain Logic
View
User Interface
User Input
Lifecycle Events
System Services
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Android Passive View
Presenter
Activity
Presentation Logic
Controller
Model
Domain Logic
View
User Interface
User Input
Lifecycle Events
System Services
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Presenter
Fake Controller
Presentation Logic
Controller
Model
Domain Logic
Stub Implementation
Passive View: Unit Tests
Presenter Test
Test Cases
Model Test
Test Cases
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Presenter
Activity
Presentation Logic
Controller
Model
Domain Logic
View
User Interface
User Input
Lifecycle Events
System Services
Passive View: UI Tests
Activity Test
Test Cases
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class LoginActivity : AppCompatActivity(), LoginView { lateinit var presenter:
LoginPresenter
override fun onCreate(savedInstanceState: Bundle?)
{ super.onCreate(savedInstanceState)
setContentView(R.layout.activity_login)
presenter = LoginPresenter(this)
login_button.setOnClickListener({
presenter.onLoginButtonClick(login_view.email, login_view.password)
})
}
// ...
}
LoginActivity.kt
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interface LoginView { fun
showUser(user: User)
fun showError(error: String)
}
LoginView.kt
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activity_login.xml
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class LoginView @JvmOverloads constructor(context: Context, attrs:
AttributeSet? = null,
defStyleAttr: Int = 0) : LinearLayout(context, attrs, defStyleAttr) { var email: String? = null
get() = login_email.text.toString()
var password: String? = null
get() = login_password.text.toString()
var error: String? = null
set(value) { login_error.text = value }
init {
(getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE)
as LayoutInflater).inflate(R.layout.view_login, this, true)
}
}
LoginView.kt
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view_login.xml
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class LoginPresenter(private val view: LoginView) { fun onLoginButtonClick(email:
String?, password: String?) {
if (email != null && password != null) {
// … get user from REST API call
if (user != null) {
view.showUser(user)
} else {
view.showError(“Invalid credentials")
}
}
}
}
LoginPresenter.kt
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class LoginActivity : AppCompatActivity(), LoginView{
// ...
override fun showUser(user: User)
{ login_view.visibility = View.GONE
user_view.visibility = View.VISIBLE
user_view.user = user
}
override fun showError(error: String)
{ login_view.error = error
}
}
LoginActivity.kt
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class UserView @JvmOverloads constructor(context: Context, attrs:
AttributeSet? = null,
defStyleAttr: Int = 0) : LinearLayout(context, attrs, defStyleAttr) { var user: User? = null
set(value) {
user_name.text = value?.name
user_email.text = value?.email
}
init {
(getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE)
as LayoutInflater).inflate(R.layout.view_user, this, true);
}
}
UserView.kt
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view_user.xml
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Android-y challenges
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Foreground/background events
Configuration change
Presenter scope
Long-running operations
Data persistence
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Android Architecture Components
Android Architecture Components
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Android Architecture Components
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Lifecycle
ViewModel
LiveData
Room
Paging Library
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Controller
LifecycleActivity
Web
Service
Activity Lifecycle
System Services
User Input
Dependency
Injection
Repository
Model
Model Storage
Presenter
View
EditText
EditText
Button
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Controller
LifecycleActivity
Web
Service
Activity Lifecycle
System Services
User Input
Dependency
Injection
Repository
Model
LiveData
Room
Storage
Presenter
ViewModel
View
EditText
EditText
Button
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Some thoughts for the future…
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Community-driven architecture
Mix and match components
Fragments?
Lifecycle aware libraries
We are all in this together
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Android Clean Architecture
BAU Mobile Application Fair
GDG
27th April 2018
Mohammed Touban