BehaviorSubjectとDagger2のCustomScopeを使ってProgressDialogをシンプルに解決したノウハウ話

1. Good-bye progress dialog mess
tsuyoyo (@tsuyogoro)
Mercari, Inc.

2. About me
tsuyoyo (@tsuyogoro)
Android engineer
Mercari, Inc

3. About this talk
● Progress dialog
● Technically
○ Show/Dismiss by BehaviorSubject (RxJava 1.x)
○ ViewModel lifecycle management with Dagger2
● Preview app
○ https://github.com/tsuyoyo/shibuya_apk_13

4. Major troubles by progress dialog...
● Dismiss at orientation change
● Remains on screen
● Suddenly crashes in the background
(since 3.0/HoneyComb)
java.lang.IllegalStateException:
Can not perform this action after onSaveInstanceState

5. My experiences
● Tough to fix bugs
● Fix would make code dirty
● Galaxy S7

6. How can we beat them?
● android:configChanges="orientation"
● No care (e.g. call API again)
● Try to manage state
○ Activity#onSaveInstanceState
○ Activity#onRetainCustomNonConfigurationInstance

7. 1. Something independent on Activity lifecycle
2. Always view can revive
3. Dialog? (not DialogFragment)

8. My idea
time
Calling API
ViewModel
View

9. Implementation idea (1) : BehaviorSubject
onNext(true);
BehaviorSubject
<Boolean>
Observer B
onNext(false);
Observer C
Observer A

10. My idea
time
Calling API
ViewModel
View
onNext
(in progress)
onNext
(complete)

11. Implementation idea (2) : Lifecycle of ViewModel
● Use Dagger2, provided by component
● Scope?
○ longer than Activity & shorter than Application
● Custom scope!!
○ Referred : Dependency injection with Dagger 2 - Custom scopes
http://frogermcs.github.io/dependency-injection-with-dagger-2-custom-scopes/

12. Custom scope
● Looks just annotation, no effect
● Application class holds the component, releases it at
end of screen
@Scope
@Retention(RetentionPolicy.RUNTIME)
@interface ViewModelScope {
}

13. Custom scope
public class MyApplication extends Application {
private MyComponent component;
public MyComponent getMyComponent() {
if (component == null) {
component = DaggerMyComponent.builder().build();
}
return component;
}
public void releaseMyComponent() {
component = null;
}
}

14. Custom scope
public class MainActivity extends AppCompatActivity {
@Inject MyViewModel myViewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
…
((MyApplication) getApplication()).getMyComponent().inject(this);
bindViewModel();
}
@Override
public void finish() {
super.finish();
((MyApplication) getApplication()).releaseMyComponent();
}

15. Summary
● Simple way to beat messy caused by ProgressDialog
● BehaviorSubject & CustomScope
● For detail
○ https://github.com/tsuyoyo/shibuya_apk_13

17. Implementation idea (1) : BehaviorSubject
private MyFakeApi api;
private BehaviorSubject<Boolean> isLoading = BehaviorSubject.create(false);
...
public Observable<Boolean> isLoading() { return isLoading.asObservable(); }
…
api.call().
.doOnSubscribe( () -> isLoading.onNext(true) )
.doOnUnsubscribe( () -> isLoading.onNext(false) )
.subscribe( /** do something */ )
...
private void bindViewModel() {
…
myViewModel.isLoading()
.observeOn(AndroidSchedulers.mainThread())
.subscribe(isLoading -> /** show/dismiss progress dialog */)
ViewModel
View