Android architecture blueprints overview

在2017年當個
潮潮der～
Android工程師
必須要知道的事
Johnny Lee 2017/1/25

2016 Android Top 10 Libraries
Ref: http://chuansong.me/n/1493021151427

為什麼需要這些東西？
“The Android framework offers a lot of flexibility
when it comes to defining how to organize and
architect an Android app. This freedom, whilst
very valuable, can also result in apps with large
classes, inconsistent naming and architectures
(or lack of) that can make testing, maintaining
and extending difficult.”
Ref: https://github.com/googlesamples/android-architecture

Android
Architecture
Blueprints
“A collection of samples to discuss and showcase different
architectural tools and patterns for Android app”
Ref: https://github.com/googlesamples/android-architecture

Outline
● Architectural patterns
○ MVP
○ MVP-Clean
● Architectural tools
○ MVP-Dagger
○ MVP-RxJava

To-do App
● Task list activity
● Task detail activity
● Add task activity
● Statistics activity

What is MVP
● View is a layer that displays data and reacts
to user actions
○ Activity
○ Fragment
○ View
● Model is a data access layer
○ Database API
○ Remote server API
● Presenter provides View with data from
Model
○ Presenter also handles background tasks
Ref: http://konmik.com/post/introduction_to_model_view_presenter_on_android/

Activity
Without MVP -
Activity is a god object

With MVP
Presenter
Model
Activity
View
Constract

View and Presenter’s creation & binding
public class TaskDetailActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
TaskDetailFragment taskDetailFragment = (TaskDetailFragment) getSupportFragmentManager()
.findFragmentById(R.id.contentFrame);
if (taskDetailFragment == null) {
taskDetailFragment = TaskDetailFragment.newInstance(taskId);
ActivityUtils.addFragmentToActivity(getSupportFragmentManager(),
taskDetailFragment, R.id.contentFrame);
}
new TaskDetailPresenter(
taskId,
Injection.provideTasksRepository(getApplicationContext()),
taskDetailFragment);
}
}
View
Presenter

@Override
TaskDetailFragment taskDetailFragment = (TaskDetailFragment) getSupportFragmentManager()
}
new TaskDetailPresenter(
taskId,
Injection.provideTasksRepository(getApplicationContext()),
taskDetailFragment);
}
}
public class TaskDetailFragment extends Fragment
implements TaskDetailContract.View {
@Override
public void setPresenter(@NonNull
TaskDetailContract.Presenter presenter)
{
mPresenter = checkNotNull(presenter);
}
}
public class TaskDetailPresenter implements TaskDetailContract.Presenter {
private final TasksRepository mTasksRepository;
private final TaskDetailContract.View mTaskDetailView;
private String mTaskId;
public TaskDetailPresenter(String taskId,
TasksRepository tasksRepository,
TaskDetailContract.View taskDetailView) {
mTaskDetailView.setPresenter(this);
}
}

Contract
public interface TaskDetailContract {
interface View extends BaseView<Presenter> {
void setLoadingIndicator(boolean active);
void showMissingTask();
void hideTitle();
void showTitle(String title);
// ...
}
interface Presenter extends BasePresenter {
void editTask();
void deleteTask();
void completeTask();
void activateTask();
}
}
public interface BaseView<T> {
void setPresenter(T
presenter);
}

View implementation
public class TaskDetailFragment extends Fragment implements TaskDetailContract.View {
@Override
public void onResume() {
mPresenter.start();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mPresenter.editTask();
}
});
return root;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_delete:
mPresenter.deleteTask();
return true;
}
return false;
}
// ...
}
Presenter operation
Presenter operation
Presenter operation

Presenter implementation
public TaskDetailPresenter(@Nullable String taskId,
@NonNull TasksRepository tasksRepository,
@NonNull TaskDetailContract.View taskDetailView) {
mTasksRepository = checkNotNull(tasksRepository, "tasksRepository cannot be null!");
mTaskDetailView = checkNotNull(taskDetailView, "taskDetailView cannot be null!");
}
@Override
public void start() { openTask(); }
private void openTask() {
mTaskDetailView.setLoadingIndicator(true);
mTasksRepository.getTask(mTaskId, new TasksDataSource.GetTaskCallback() {
@Override
public void onTaskLoaded(Task task) {
mTaskDetailView.setLoadingIndicator(false);
showTask(task);
}
@Override
public void onDataNotAvailable() {
mTaskDetailView.showMissingTask();
}
});
}
// ...
}
View operation
View operation
View operation
View operation
Model operation

public class TasksRepository implements TasksDataSource {
private static TasksRepository INSTANCE = null;
private final TasksDataSource mTasksRemoteDataSource;
private final TasksDataSource mTasksLocalDataSource;
private TasksRepository(@NonNull TasksDataSource tasksRemoteDataSource,
@NonNull TasksDataSource tasksLocalDataSource) {
mTasksRemoteDataSource = checkNotNull(tasksRemoteDataSource);
mTasksLocalDataSource = checkNotNull(tasksLocalDataSource);
}
public static TasksRepository getInstance(TasksDataSource tasksRemoteDataSource,
TasksDataSource tasksLocalDataSource) {
if (INSTANCE == null) {
INSTANCE = new TasksRepository(tasksRemoteDataSource,
tasksLocalDataSource);
}
return INSTANCE;
}
// ...
}
Model implementation

private static TasksRepository INSTANCE = null;
}
public static TasksRepository getInstance(TasksDataSource tasksRemoteDataSource,
TasksDataSource tasksLocalDataSource) {
if (INSTANCE == null) {
INSTANCE = new TasksRepository(tasksRemoteDataSource,
tasksLocalDataSource);
}
return INSTANCE;
}
// ...
}
public interface TasksDataSource {
interface LoadTasksCallback {
void onTasksLoaded(List<Task> tasks);
void onDataNotAvailable();
}
interface GetTaskCallback {
void onTaskLoaded(Task task);
void onDataNotAvailable();
}
void getTasks(@NonNull LoadTasksCallback callback);
void getTask(@NonNull String taskId,
@NonNull GetTaskCallback callback);
void saveTask(@NonNull Task task);
void completeTask(@NonNull Task task);
void completeTask(@NonNull String taskId);
void activateTask(@NonNull Task task);
void activateTask(@NonNull String taskId);
void clearCompletedTasks();
void refreshTasks();
void deleteAllTasks();
void deleteTask(@NonNull String taskId);
}

public void getTasks(@NonNull final LoadTasksCallback callback) {
if (mCachedTasks != null && !mCacheIsDirty) {
callback.onTasksLoaded(new ArrayList<>(mCachedTasks.values()));
return;
}
if (mCacheIsDirty) {
getTasksFromRemoteDataSource(callback);
} else {
mTasksLocalDataSource.getTasks(new LoadTasksCallback() {
@Override
public void onTasksLoaded(List<Task> tasks) {
refreshCache(tasks);
callback.onTasksLoaded(new ArrayList<>(mCachedTasks.values()));
}
@Override
getTasksFromRemoteDataSource(callback);
}
});
}
}
}
Respond immediately with cache if available and not dirty
If the cache is dirty we need to fetch new data from the
network.
Query the local storage if available. If not, query the
network.

What is Clean Architecture
Ref: https://en.wikipedia.org/wiki/Robert_Cecil_Martin

Dependency Rule: source code dependencies can only point inwards and nothing in an
inner circle can know anything at all about something in an outer circle.
Ref: http://fernandocejas.com/2014/09/03/architecting-android-the-clean-way/

● Entities
○ These are the business objects of the application.
● Use Cases
○ These use cases orchestrate the flow of data to and from the
entities. Are also called Interactors.
● Interface Adapters (Presenter)
○ This set of adapters convert data from the format most
convenient for the use cases and entities. Presenters and
Controllers belong here.
● Frameworks and Drivers (UI)
○ This is where all the details go: UI, tools, frameworks, etc.
Ref: http://fernandocejas.com/2014/09/03/architecting-android-the-clean-way/

● Independent of Frameworks
● Testable
○ Business rules (Use cases) can be tested without external
element
● Independent of UI
○ The UI can change easily, without changing the rest of the
system
● Independent of Database
○ Business rules (Use cases) are not bound to the database
● Independent of any external agency
○ Business rules (Use cases) don’t know anything at all about
the outside world
Ref: https://8thlight.com/blog/uncle-bob/2012/08/13/the-clean-architecture.html

private final UseCaseHandler mUseCaseHandler;
private final GetTask mGetTask;
private final CompleteTask mCompleteTask;
private final ActivateTask mActivateTask;
private final DeleteTask mDeleteTask;
public TaskDetailPresenter(@NonNull UseCaseHandler useCaseHandler,
@Nullable String taskId,
@NonNull TaskDetailContract.View taskDetailView,
@NonNull GetTask getTask,
@NonNull CompleteTask completeTask,
@NonNull ActivateTask activateTask,
@NonNull DeleteTask deleteTask) {
mUseCaseHandler = checkNotNull(useCaseHandler, "useCaseHandler cannot be null!");
mGetTask = checkNotNull(getTask, "getTask cannot be null!");
mCompleteTask = checkNotNull(completeTask, "completeTask cannot be null!");
mActivateTask = checkNotNull(activateTask, "activateTask cannot be null!");
mDeleteTask = checkNotNull(deleteTask, "deleteTask cannot be null!");
}
}
Use case
Background executor

mUseCaseHandler.execute(mGetTask, new GetTask.RequestValues(mTaskId),
new UseCase.UseCaseCallback<GetTask.ResponseValue>() {
@Override
public void onSuccess(GetTask.ResponseValue response) {
Task task = response.getTask();
mTaskDetailView.setLoadingIndicator(false);
showTask(task);
}
@Override
public void onError() {
}
});
}
}
View operation
View operation
View operation
View operation
Model operation

Use case implementation
public class GetTask extends UseCase<GetTask.RequestValues, GetTask.ResponseValue> {
public GetTask(@NonNull TasksRepository tasksRepository) {
}
@Override
protected void executeUseCase(final RequestValues values) {
mTasksRepository.getTask(values.getTaskId(), new TasksDataSource.GetTaskCallback() {
@Override
public void onTaskLoaded(Task task) {
if (task != null) {
ResponseValue responseValue = new ResponseValue(task);
getUseCaseCallback().onSuccess(responseValue);
} else {
getUseCaseCallback().onError();
}
}
@Override
getUseCaseCallback().onError();
}
});
}
}

What is RxJava
“RxJava is a Java VM implementation of Reactive Extensions: a
library for composing asynchronous and event-based programs
by using observable sequences.”
“It extends the observer pattern to support sequences of
data/events and adds operators that allow you to compose
sequences together declaratively while abstracting away
concerns about things like low-level threading, synchronization,
thread-safety and concurrent data structures.”
Ref: https://github.com/ReactiveX/RxJava

View implementation
public class TaskDetailFragment extends Fragment implements TaskDetailContract.View {
@Override
public void onResume() {
super.onResume();
mPresenter.subscribe();
}
@Override
public void onPause() {
super.onPause();
mPresenter.unsubscribe();
}
@Override
public void setPresenter(@NonNull TaskDetailContract.Presenter presenter) {
mPresenter = checkNotNull(presenter);
}
}

@NonNull private final TasksRepository mTasksRepository;
@NonNull private final TaskDetailContract.View mTaskDetailView;
@NonNull private final BaseSchedulerProvider mSchedulerProvider;
@NonNull private CompositeSubscription mSubscriptions;
public TaskDetailPresenter(@Nullable String taskId,
@NonNull TasksRepository tasksRepository,
@NonNull TaskDetailContract.View taskDetailView,
@NonNull BaseSchedulerProvider schedulerProvider) {
mSchedulerProvider = checkNotNull(schedulerProvider, "schedulerProvider cannot be null");
mSubscriptions = new CompositeSubscription();
}
@Override
public void subscribe() {
openTask();
}
@Override
public void unsubscribe() {
mSubscriptions.clear();
}
}

private final BaseSchedulerProvider mSchedulerProvider;
private CompositeSubscription mSubscriptions;
if (Strings.isNullOrEmpty(mTaskId)) {
return;
}
mSubscriptions.add(mTasksRepository
.getTask(mTaskId)
.subscribeOn(mSchedulerProvider.computation())
.observeOn(mSchedulerProvider.ui())
.subscribe(
// onNext
this::showTask,
// onError
throwable -> {
},
// onCompleted
() -> mTaskDetailView.setLoadingIndicator(false)));
}
}
View operation
View operation
View operation
View operation
Model operation

@VisibleForTesting Map<String, Task> mCachedTasks;
@VisibleForTesting boolean mCacheIsDirty = false;
}
@Override
public Observable<List<Task>> getTasks() {
return Observable.from(mCachedTasks.values()).toList();
} else if (mCachedTasks == null) {
mCachedTasks = new LinkedHashMap<>();
}
Observable<List<Task>> remoteTasks = getAndSaveRemoteTasks();
return remoteTasks;
} else {
Observable<List<Task>> localTasks = getAndCacheLocalTasks();
return Observable.concat(localTasks, remoteTasks)
.filter(tasks -> !tasks.isEmpty())
.first();
}
}
}
Observer pattern
Compose sequences

@VisibleForTesting Map<String, Task> mCachedTasks;
@VisibleForTesting boolean mCacheIsDirty = false;
}
@Override
public Observable<List<Task>> getTasks() {
return Observable.from(mCachedTasks.values()).toList();
} else if (mCachedTasks == null) {
mCachedTasks = new LinkedHashMap<>();
}
Observable<List<Task>> remoteTasks = getAndSaveRemoteTasks();
return remoteTasks;
} else {
Observable<List<Task>> localTasks = getAndCacheLocalTasks();
return Observable.concat(localTasks, remoteTasks)
.filter(tasks -> !tasks.isEmpty())
.first();
}
}
}
private Observable<List<Task>> getAndCacheLocalTasks() {
return mTasksLocalDataSource.getTasks()
.flatMap(new Func1<List<Task>, Observable<List<Task>>>() {
@Override
public Observable<List<Task>> call(List<Task> tasks) {
return Observable.from(tasks)
.doOnNext(task ->
mCachedTasks.put(task.getId(), task))
.toList();
}
});
}
private Observable<List<Task>> getAndSaveRemoteTasks() {
return mTasksRemoteDataSource
.getTasks()
.flatMap(new Func1<List<Task>, Observable<List<Task>>>() {
@Override
public Observable<List<Task>> call(List<Task> tasks) {
return Observable.from(tasks).doOnNext(task -> {
mTasksLocalDataSource.saveTask(task);
mCachedTasks.put(task.getId(), task);
}).toList();
}
})
.doOnCompleted(() -> mCacheIsDirty = false);
}

What is Dagger
“Dagger is a fully static, compile-time dependency injection
framework for both Java and Android. It is an adaptation of an
earlier version created by Square and now maintained by
Google.”
“Dagger is a replacement for FactoryFactory classes that
implements the dependency injection design pattern without the
burden of writing the boilerplate. It allows you to focus on the
interesting classes. Declare dependencies, specify how to satisfy
them, and ship your app.”
Ref: https://google.github.io/dagger/

@Inject TaskDetailPresenter mTaskDetailPresenter;
@Override
TaskDetailFragment taskDetailFragment =
(TaskDetailFragment) getSupportFragmentManager()
}
DaggerTaskDetailComponent.builder()
.taskDetailPresenterModule(
new TaskDetailPresenterModule(taskDetailFragment,
taskId))
.tasksRepositoryComponent(((ToDoApplication) getApplication())
.getTasksRepositoryComponent()).build()
.inject(this);
}
}
Field injection
Inject presenter
Provide view

Dagger configuration
@Override
// ...
new TaskDetailPresenterModule(taskDetailFragment, taskId))
.inject(this);
}
}
@FragmentScoped
@Component(dependencies = TasksRepositoryComponent.class,
modules = TaskDetailPresenterModule.class)
public interface TaskDetailComponent {
void inject(TaskDetailActivity taskDetailActivity);
}

@Override
// ...
.inject(this);
}
}
@Module
public class TaskDetailPresenterModule {
private final TaskDetailContract.View mView;
private final String mTaskId;
public TaskDetailPresenterModule(
TaskDetailContract.View view, String taskId) {
mView = view;
mTaskId = taskId;
}
@Provides
TaskDetailContract.View provideTaskDetailContractView() {
return mView;
}
@Provides
String provideTaskId() {
return mTaskId;
}
}

@Override
// ...
.inject(this);
}
} @Singleton
@Component(modules = {TasksRepositoryModule.class,
ApplicationModule.class})
public interface TasksRepositoryComponent {
TasksRepository getTasksRepository();
}
@Module
public class TasksRepositoryModule {
@Singleton @Provides @Local
TasksDataSource provideTasksLocalDataSource(Context context) {
return new TasksLocalDataSource(context);
}
@Singleton @Provides @Remote
TasksDataSource provideTasksRemoteDataSource() {
return new FakeTasksRemoteDataSource();
}
}
@Module
public final class ApplicationModule {
private final Context mContext;
ApplicationModule(Context context) {
mContext = context;
}
@Provides
Context provideContext() {
return mContext;
}
}

final class TaskDetailPresenter implements TaskDetailContract.Presenter
{
private TasksRepository mTasksRepository;
private TaskDetailContract.View mTaskDetailView;
@Nullable String mTaskId;
@Inject
TaskDetailPresenter(@Nullable String taskId,
TasksRepository tasksRepository,
TaskDetailContract.View taskDetailView) {
mTasksRepository = tasksRepository;
mTaskDetailView = taskDetailView;
mTaskId = taskId;
}
@Inject
void setupListeners() {
}
}
Constructor
injection
Method
injection

Reference
● Android Architecture Blueprints
● Architecting Android…The clean
way?
● The Clean Architecture
● Introduction to Model View
Presenter on Android

Android architecture blueprints overview

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