The document discusses modern app architecture using Dagger 2 for dependency injection and RxJava for asynchronous data flows. It covers dependency injection and how Dagger 2 avoids reflection for faster performance. It also discusses the model-view-presenter pattern to separate business logic from display logic. Finally, it explains how RxJava uses observables and observers to implement asynchronous data streams and how this avoids callback hell and allows pushing data instead of polling.

1. •Moderne App-Architektur mit
Dagger2 und RxJava
•
code.talks 2015
Martin Breuer
http://www.gedankensuppe.de/hamburg

2. Dominik Helleberg
+DominikHelleberg
Mobile Application Development
Tools
Android / Embedded

3. Angelo Rüggeberg
+AngeloRüggeberg
Google Developer Group, Munich | Lead
Mobile Application Development
Android Enthusiast
Since Cupcake (Version 1.5)

4. Why?
App Architektur

5. App Architektur

6. App Architektur
Themen
• Dependency Injection
• MV(i)P
• RxJava

7. Dependency Injection
• Your class get’s what it needs (Dependenciescome
to you)
• You have no idea where they come from
• A well known pattern
• Everyone uses it (more or less)
App Architektur
Dependency Injection

8. Dependency Injection
• It’s common sense on the server side
• There are already frameworks out there:
–Spring DI
–Google Guice
–Pico Container
–...
App Architektur
Dependency Injection

9. Dependency Injection - Android
Now what about android?
• Mobile (limited ressources)
• App Startup time does really matter
• Reflection is slow
• App Size + method count does really matter
App Architektur
Dependency Injection

10. Dagger 2
Why another Framework?
• no reflection at all
• Based on Dagger1
• Proposed + Implemented by the Java Core Team (Google)
• Code generation (As if you would write it)
App Architektur
Dependency Injection

11. Dagger 2 - Basics
@Modules / @Provides
• Provide Dependenciesto
@Inject
• Requests for Dependencies
@Components
• Public API, the Bridge between Modules and Injects
and some more...
App Architektur
Dependency Injection

12. Dagger2
TwitterTimeline
(interface)
TwitterTimeline RestAdapter
MockTwitter
Timeline
HTTPClient
App Architektur
Dependency Injection

13. Dagger2
TwitterTimeline
RestAdapter
MockTwitter
Timeline
MockNetworkModule
NetworkModule
ApplicationComponent
Mock
ApplicationComponent
App Architektur
Dependency Injection

14. @Singleton
@Component
(modules = {ApplicationModule.class, NetworkingModule.class})
public interface ApplicationComponent {
MVPComponent plus();;
}
App Architektur
Dependency Injection

15. @Module
public class NetworkingModule {
@Provides
@Singleton
TwitterTimeline provideTwitterTimeline(RestAdapter restAdapter) {
return restAdapter.create(TwitterTimeline.class);;
}
@Provides
@Singleton
public RestAdapter provideRestAdapter(SigningOkClient client) {
return TwitterApiAdapter.getInstance(client);;
}
App Architektur
Dependency Injection

16. @Inject
TwitterTimeline timeline;;
App Architektur
Dependency Injection

17. @Module
public class MockNetworkingModule extends NetworkingModule {
@Provides
@Singleton
TwitterTimeline provideTwitterTimeline() {
return new MockTwitterTimeline();;
}
}
App Architektur
Dependency Injection

18. Dagger2
• DI is a good thing to have
• steep learning curve
• Sometimes hard to get hold on component
references
• Still under active development
• Enforces structured code
• Code generation is a good thing
App Architektur
Dependency Injection

19. Model View Presenter (MViP)
• Seperate Business Logic, Application Logic, Display
Logic
• Change independent parts without Issues
• Easier to Test
–Mock Network Modules etc.
App Architektur
MViP

20. MViP: Components
• Model
–Data that is represented
–for example Tweets
• View
–The View Displaying the Data
–can be Activity, Fragment, CustomView
• Presenter
–Logic
–for example fetching Tweets from Network
App Architektur
MViP

21. MVP: Components
https://blog.8thlight.com/uncle-­bob/2012/08/13/the-­clean-­architecture.html
App Architektur
MViP

22. Example
App Architektur
MViP

23. App Architektur
MViP
Activity
fetchFeed()
updateFeed(List Feed)
updateListitem(item)
onTextChanged()

24. MViP: Model
• The Data that is displayed to the User
• Data used to do Interactions with the Presenter
• Can be the same as the Models for Network
Requests
–Retrofit
App Architektur
MViP

25. public class Tweet {
@JsonProperty("created_at")
private String DateCreated;;
@JsonProperty("id")
private long Id;;
@JsonProperty("text")
private String Text;;
@JsonProperty("user")
private TwitterUser User;;
}
App Architektur
MViP -­‐ Model

26. • Interface
• Actual Display Unit Implements Interface
–Fragment, Activity, Custom View, whatever…
• Views should be dumb!
–Only react to Actions
• No Business Logic in here
MVP: View
App Architektur
MViP

27. public interface TwitterTimelineView {
void showLoading();;
void hideLoading();;
void showFeed(List<Tweet> messages);;
void showError(String errorMessage);;
}
App Architektur
MViP -­‐ View

28. class HashtagFeedActivity extends BaseActivity implements
TwitterTimelineView {
@Override
public void showLoading() { … }
@Override
public void hideLoading() { … }
@Override
public void showFeed(List<Tweet> messages) { … }
@Override
public void showError(String errorMessage) { … }
App Architektur
MViP -­‐ View

29. class HashtagFeedActivity extends BaseActivity implements
TwitterTimelineView {
@Override
public void showLoading() { … }
@Override
public void hideLoading() { … }
@Override
public void showFeed(List<Tweet> messages) { … }
@Override
public void showError(String errorMessage) { … }
App Architektur
MViP -­‐ View

30. class HashtagFeedActivity extends BaseActivity implements
TwitterTimelineView {
@Override
public void showLoading() { … }
@Override
public void hideLoading() { … }
@Override
public void showFeed(List<Tweet> messages) { … }
@Override
public void showError(String errorMessage) { … }
App Architektur
MViP -­‐ View

31. Presenter
• Interface
• Binds to the View
• Business Logic in here
App Architektur
MViP

32. public interface Presenter<T> {
void onDestroy();;
void bindView(T view);;
void unbindView();;
}
App Architektur
MViP -­‐ Presenter

33. public interface TwitterHashtagTimelinePresenter
extends Presenter<TwitterTimelineView>{
void bindSearchView(EditText textView);;
void loadHashtagTimeline(String hashtag);;
void goToDetails(Activity context, Tweet t);;
}
App Architektur
MViP -­‐ Presenter

34. public interface TwitterHashtagTimelinePresenter
extends Presenter<TwitterTimelineView>{
void bindSearchView(EditText textView);;
void loadHashtagTimeline(String hashtag);;
void goToDetails(Activity context, Tweet t);;
}
App Architektur
MViP -­‐ Presenter

35. public class TwitterHashtagTimelinePresenterImpl
implements TwitterHashtagTimelinePresenter {
private TwitterTimelineView view;;
@Override
public void bindView(TwitterTimelineView view) {
this.view = view;;
}
@Override
public void loadHashtagTimeline(String hashtag) {
… Do Network Request ...
}
App Architektur
MViP -­‐ Presenter

36. public class TwitterHashtagTimelinePresenterImpl
implements TwitterHashtagTimelinePresenter {
private TwitterTimelineView view;;
@Override
public void bindView(TwitterTimelineView view) {
this.view = view;;
}
@Override
public void loadHashtagTimeline(String hashtag) {
… Do Network Request ...
}
App Architektur
MViP -­‐ Presenter

37. public class TwitterHashtagTimelinePresenterImpl
implements TwitterHashtagTimelinePresenter {
private TwitterTimelineView view;;
@Override
public void bindView(TwitterTimelineView view) {
this.view = view;;
}
@Override
public void loadHashtagTimeline(String hashtag) {
… Do Network Request ...
}
App Architektur
MViP -­‐ Presenter

38. public class TwitterHashtagTimelinePresenterImpl
implements TwitterHashtagTimelinePresenter {
private TwitterTimelineView view;;
@Override
public void bindView(TwitterTimelineView view) {
this.view = view;;
}
@Override
public void loadHashtagTimeline(String hashtag) {
… Do Network Request ...
}
App Architektur
MViP -­‐ Presenter

39. @Override
public void loadHashtagTimeline(String hashtag) {
view.showLoading();;
List<Tweet> tweets = interactor.loadHashtagTweets(hashtag);;
view.showTweets(tweets);;
view.hideLoading();;
}
App Architektur
MViP -­‐ Presenter

40. @Override
public void loadHashtagTimeline(String hashtag) {
view.showLoading();;
List<Tweet> tweets = interactor.loadHashtagTweets(hashtag);;
view.showTweets(tweets);;
view.hideLoading();;
}
App Architektur
MViP -­‐ Presenter

41. @Override
public void loadHashtagTimeline(String hashtag) {
view.showLoading();;
List<Tweet> tweets = interactor.loadHashtagTweets(hashtag);;
view.showTweets(tweets);;
view.hideLoading();;
}
App Architektur
MViP -­‐ Presenter

42. Interactor?
• Do not bloat up Presenters!
• Interactors are used for doing things
–Fetching Stuff from the network
–Fetching Stuff from Disk
• Interface again!
App Architektur
MViP -­‐ interactor

43. public interface TwitterTimelineInteractor {
void loadUserTweets(Observer<? super List<Tweet>>
observer, String username);;
void loadHashtagTweets(Observer<? super List<Tweet>>
observer, String hastag);;
Observable<List<Tweet>> loadHashtagTweets(String
hashtag);;
void pollHashtagTweets(Observer<? super List<Tweet>>
observer, String hashtag);;
}
App Architektur
MViP -­‐ interactor

44. public class TwitterTimelineInteractorImpl
implements TwitterTimelineInteractor {
TwitterTimeline twitterTimeline;;
@Override
public void loadUserTweets(Observer<? super List<Tweet>>
observer, String username) {
twitterTimeline
.getUserTimeline(username)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(observer);;
}
App Architektur
MViP -­‐ interactor

45. App Architektur
Summary
Activity
textChangeObservable
Presenter
bindView()
Adapter
showFeed()
setTweets()
loadHashtagTimelineFeed
showFeed()
Interactor
loadHashtagTimeline

46. Why?
• Push don’t Poll!
–do not stress the UI
–do not stress the Application
• Avoid Lifecycle Problems
• Avoid the Callback Hell
• Death to:
–Boilerplate Code
–AsyncTasks, Timertasks, Loaders, etc...
App Architektur
RXJava

47. RX: What?
• Programming Paradigm based on asynchronous
Data Flow
• Idea from the late 90s
• Erik Meijer (Microsoft) developed first RX extension
for .NET
• Adapted by many Programming languages
App Architektur
RXJava

48. RX: What?
• Ported to JVM by Ben Christensen and Jafar Husain
(Netflix)
–Java, Closure, Groovy, Scala, etc etc….
• RXJava -> RXAndroid
• The Observer pattern done right.
App Architektur
RXJava
http://reactivex.io/

49. RX: What?
App Architektur
RXJava

50. RXAndroid: How?
• Producing Entities:
–Observables
–Subjects
• Consuming Entities:
–Observers
–Subscribers
• Consuming Entities subscribe to Producing Entities
App Architektur
RXJava

51. RXAndroid: Setup
compile 'io.reactivex:rxandroid:1.0.1'
//optional
compile 'io.reactivex:rxjava:1.0.14'
App Architektur
RXJava

52. Observers
Lifecycle:
–onNext(T):
• gets called when new Data is emited with the
Data
–onCompleted():
• gets called when the Sequence is done
–onError(Throwable):
• gets called when an Error occured
App Architektur
RXJava

53. Observables
• Sequence that emits data
–can emit more than once
• Lives as long as there is work to do
• Observers subscribe to an Observable
• When there is no Subscriber, the Observable emits
the data nowhere
App Architektur
RXJava

54. Sequence Example
Observable
Emits Something every Second
App Architektur
RXJava

55. Sequence Example
Observable
Observer
Subscribe Unsubscribe
onNext(T);;
App Architektur
RXJava

56. Observable<Long> interval = Observable
.interval(1, TimeUnit.SECONDS);;
App Architektur
RXJava

57. interval.subscribe(new Observer<Long>() {
@Override
public void onCompleted() {
Timber.d("onCompleted");;
}
@Override
public void onError(Throwable e) {
Timber.e(e, e.getMessage());;
}
@Override
public void onNext(Long aLong) {
Timber.d("Tick: " + aLong.toString());;
App Architektur
RXJava

58. Transforming the Data
• We do not want a Long as result, we want a String
• map()
–gets the Long value
–returns a String value
• Chainable!
–map().map().map().map().............map()
App Architektur
RXJava

59. Observable<String> interval = Observable
.interval(1, TimeUnit.SECONDS)
.map(new Func1<Long, String>() {
@Override
public String call(Long aLong) {
return "Tick: " + aLong.toString();;
}
});;
App Architektur
RXJava

60. Observable<String> interval = Observable
.interval(1, TimeUnit.SECONDS)
.map(new Func1<Long, String>() {
@Override
public String call(Long aLong) {
return "Tick: " + aLong.toString();;
}
});;
App Architektur
RXJava

61. Observable<String> interval = Observable
.interval(1, TimeUnit.SECONDS)
.map(new Func1<Long, String>() {
@Override
public String call(Long aLong) {
return "Tick: " + aLong.toString();;
}
});;
Returns Long
App Architektur
RXJava

62. Observable<String> interval = Observable
.interval(1, TimeUnit.SECONDS)
.map(new Func1<Long, String>() {
@Override
public String call(Long aLong) {
return "Tick: " + aLong.toString();;
}
});;
Takes the Long
Transforms the Data
and returns a String
App Architektur
RXJava

63. Hello Again Boilerplatecode
• new Func1<T, T>() { public T call(t t2) { … } for every
mapping will turn the code really unreadable and
bloated
• Lambda to the Rescue!
–retrolambda for android & gradle
–https://github.com/evant/gradle-retrolambda
App Architektur
RXJava

64. Observable<String> interval = Observable
.interval(1, TimeUnit.SECONDS)
.map(new Func1<Long, String>() {
@Override
public String call(Long aLong) {
return "Tick: " + aLong.toString();;
}
});;
App Architektur
RXJava

65. Observable<String> interval = Observable
.interval(1, TimeUnit.SECONDS)
.map(aLong -­> "Tick: " + aLong.toString());;
App Architektur
RXJava

66. Observable<String> interval = Observable
.interval(1, TimeUnit.SECONDS)
.map(aLong -­> aLong.toString())
.map(string -­> "Tick: " + string);;
App Architektur
RXJava

67. Combining Observables
• Prevent Callback hell
• Easy to Synchronize for async Operations
• Running 2 Network Calls and combine the
Results
• Combine onTextChanged events from two fields
• etc.
• .zip(), combineLatest()
App Architektur
RXJava

68. Observable.combineLatest(
WidgetObservable.text(txt1, false),
WidgetObservable.text(txt2, false),
(event1, event2) -­> event1.text().toString() +
event2.text().toString()
).subscribe(combined -­> {
Timber.d(combined);;
});;
App Architektur
RXJava

69. Observable.combineLatest(
WidgetObservable.text(txt1, false),
WidgetObservable.text(txt2, false),
(event1, event2) -­> event1.text().toString() +
event2.text().toString()
).subscribe(combined -­> {
Timber.d(combined);;
});;
App Architektur
RXJava

70. Observable.combineLatest(
WidgetObservable.text(txt1, false),
WidgetObservable.text(txt2, false),
(event1, event2) -­> event1.text().toString() +
event2.text().toString()
).subscribe(combined -­> {
Timber.d(combined);;
});;
App Architektur
RXJava

71. Observable.combineLatest(
WidgetObservable.text(txt1, false),
WidgetObservable.text(txt2, false),
(event1, event2) -­> event1.text().toString() +
event2.text().toString()
).subscribe(combined -­> {
Timber.d(combined);;
});;
App Architektur
RXJava

72. Observable.combineLatest(
WidgetObservable.text(txt1, false),
WidgetObservable.text(txt2, false),
(event1, event2) -­> event1.text().toString() +
event2.text().toString()
).subscribe(combined -­> {
Timber.d(combined);;
});;
App Architektur
RXJava

73. Example: Livesearch
• Retrieve the user Input from a EditText when text
changes
–only after nothing changes for 600 ms
• Add # infront of the input to do a hastag search
• Call the network (via Retrofit)
–returns StatusesResponse Object
• Transform to List<Tweets>
• Show Tweets in view
App Architektur
RXJava

74. textChangeObservable
.observeOn(AndroidSchedulers.mainThread())

75. textChangeObservable
.observeOn(AndroidSchedulers.mainThread())
.map(onTextChangeEvent -­> onTextChangeEvent.text().toString())

76. textChangeObservable
.observeOn(AndroidSchedulers.mainThread())
.map(onTextChangeEvent -­> onTextChangeEvent.text().toString())
.map(searchText -­> "#" + searchText)

77. textChangeObservable
.observeOn(AndroidSchedulers.mainThread())
.map(onTextChangeEvent -­> onTextChangeEvent.text().toString())
.map(searchText -­> "#" + searchText)
.subscribe(
tag -­> {
Timber.d(tag);;
loadHashtagTimeline(tag);;
}

78. textChangeObservable
.observeOn(AndroidSchedulers.mainThread())
.map(onTextChangeEvent -­> onTextChangeEvent.text().toString())
.map(searchText -­> "#" + searchText)
.subscribe(
tag -­> {
Timber.d(tag);;
loadHashtagTimeline(tag);;
},
e -­> {
Timber.e(e, e.getMessage());;
view.showError(e.getMessage());;
} );;

79. textChangeObservable
.debounce(600, TimeUnit.MILLISECONDS)
.observeOn(AndroidSchedulers.mainThread())
.map(onTextChangeEvent -­> onTextChangeEvent.text().toString())
.map(searchText -­> "#" + searchText)
.subscribe(
tag -­> {
Timber.d(tag);;
loadHashtagTimeline(tag);;
},
e -­> {
Timber.e(e, e.getMessage());;
view.showError(e.getMessage());;
} );;

80. Demo

81. Thank You!