From Legacy to Hexagonal (An Unexpected Android Journey)

From Legacy to Hexagonal
(An Unexpected Android Journey)
Rubén Serrano @Akelael
Lead Android Developer @RedboothHQ
José Manuel Pereira @JMPergar
Android Software Engineer @RedboothHQ

Agenda
1. From Legacy Code
2. Towards Hexagonal Architecture
3. To infinity, and beyond!

One dev from a contractor
+ one senior iOS dev

+ one junior iOS dev

A different Android dev

A different Android dev
+ one confused Android team

1. We have a huge technical debt

1. We have huge technical debt
2. We can’t stop developing new features

1. We have huge technical debt
2. We can’t stop developing new features
3. We can’t remove debt at this point and we
shouldn’t add any more

What have we
learnt from pizza?

You just don’t
eat the whole
pizza at once

1. Slice the big methods into small
meaningful methods

meaningful methods
2. Identify different responsibilities and move
them to other classes

meaningful methods
2. Identify different responsibilities and move
them to other classes
3. Use less coupled framework components
(or no components at all)

Notifies
events
View
Presenter
Model

Requests
data
View
Presenter
Model

Serves data
View
Presenter
Model

Change data
representation
View
Presenter
Model

View
Tells how to draw
Presenter
Model

Layout
+
Activity/
Fragment
Presenter
Data
+
Business logic

In code
(Original code…)
http://goo.gl/z5Xn2J

listAdapter =
MainFragment
new SimpleCursorAdapter(getActivity(),
android.R.layout.simple_list_item_1,
null,
new String[]{FakeDatabase.COLUMN_NAME},
new int[]{android.R.id.text1},
0);
listView.setAdapter(listAdapter);

getLoaderManager().initLoader(0, null, new LoaderManager.LoaderCallbacks<Cursor>() {
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
return new CursorLoader(getActivity(), MainContentProvider.URI,
null, null, null, null);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
listAdapter.swapCursor(data);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
listAdapter.swapCursor(null);
}
});
MainFragment

In Code
(… to MVP)
http://goo.gl/Retvli

MainView & MainModel
public interface MainView {
public void swaplListData(Cursor cursor);
}
public interface MainModel {
public void setPresenter(MainPresenter presenter);
public void startLoadingData(Context context);
}

MainFragment
public class MainFragment extends Fragment implements MainView {
//...
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
presenter = PresenterFactory.getMainPresenter(this);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
//...
presenter.notifyOnCreate(getActivity());
}
@Override
public void swaplListData(Cursor cursor) {
listAdapter.swapCursor(cursor);
}

MainPresenter
public class MainPresenter {
private MainView mainView;
private MainModel mainModel;
//...
public void notifyOnCreate(Context context) {
mainModel.startLoadingData(context);
}
public void notifiyLoadedDataAvailable(Cursor cursor) {
mainView.swaplListData(cursor);
}
}

PresenterFactory
public class PresenterFactory {
public static MainPresenter getMainPresenter(MainView view) {
MainModel model = new MainCursorModel();
return MainPresenter.newInstance(view, model);
}
}

MainCursorModel
public class MainCursorModel implements MainModel {
//...
@Override
public void startLoadingData(Context context) {
new LoadDataAsyncTask().execute(context);
}
private class LoadDataAsyncTask extends AsyncTask<Context, Void, Cursor > {
//...
@Override
protected void onPostExecute(Cursor result) {
super.onPostExecute(result);
presenter.notifiyLoadedDataAvailable(result);
}
}
}

Pros & Cons
View decoupled from model
Cleaner code and smaller fragment/activities
View and model not really decoupled (cursor)
All the components use the framework

Layout
+
Activity/
Fragment
Data domain
Business
logic

Layout
+
Activity/
Fragment
Database
Business
logic
Network
Sensors

Database
Network
Sensors
Layout
+
Activity/
Fragment
Business
logic

Business
logic
Sensors
Network
Database
Layout
+
Activity/
Fragment

Port
Business
logic Port Port
Port
Sensors
Network
Database
Layout
+
Activity/
Fragment

Adapter
Port
Business
logic Port Port
Sensors
Network
Database
Layout
+
Activity/
Fragment
Adapter Adapter
Port
Adapter

Boundary
Port
Business
logic Port Port
Sensors
Network
Database
Layout
+
Activity/
Fragment
Boundary Boundary
Port
Boundary

App
Core
App App
Module Core
Module
App
Module
App
Module
App
Module
App
Core Core
Core
App

In code
(Hexagonal)
http://goo.gl/lIyH0o

MainFragment
public class MainFragment extends Fragment {
//...
private MainFragmentBoundary viewBoundary;
@Override
public void onCreate(Bundle savedInstanceState) {
//...
viewBoundary = MainFragmentBoundary.newInstance(this);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
//...
viewBoundary.notifyOnCreate();
}

MainFragment
public void setListAdapter() {
listAdapter = new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1,
android.R.id.text1,
new ArrayList<String>(0));
listView.setAdapter(listAdapter);
}
public void swapList(List<String> names) {
listAdapter.clear();
listAdapter.addAll(names);
}

MainFragmentBoundary
public class MainFragmentBoundary implements MainViewPort {
private MainFragment mainFragment;
private MainLogic logic;
//...
public void notifyOnCreate() {
logic.notifyOnCreate();
}
@Override
public void swaplListData(List<String> names) {
mainFragment.swapList(names);
}

MainModelBoundary
public class MainModelBoundary implements MainModelPort {
private MainLogic logic;
private MainRepository repository;
//...
@Override
public void startLoadingData() {
repository.startLoadingData(new MainRepository.OnDataLoadedListener() {
@Override
public void onDataLodaded(Cursor cursor) {
notifyDataLoaded(cursor);
}
});
}
private void notifyDataLoaded(Cursor cursor) {
List<String> names = mapCursorToList(cursor);
logic.notifiyLoadedDataAvailable(names);
}

MainModelBoundary
private List<String> mapCursorToList(Cursor cursor) {
List<String> names = new ArrayList<String>();
int nameColumnIndex = cursor.getColumnIndex(FakeDatabase.COLUMN_NAME);
while (cursor.moveToNext()) {
String name = cursor.getString(nameColumnIndex);
names.add(name);
}
return names;
}

Pros & Cons
Logic is not going to be affected by framework changes
Logic is pure Java: easier to test
Less changes when replacing a plugin
Easier for 2 devs to work on the same feature
More complex architecture
Need to map each POJO for each layer
What happens when the plugins need to cooperate?

Model
Plugin
Layout
+
Activity/
Fragment
Boundary Business Boundary
logic Port Port

Create task
Send chat message
Update note
Request projects
Business
logic
Port Model
Plugin
Boundary

We don’t like:
callback’s hell + AsyncTasks

We don’t like:
We don’t mind (but could be a problem):
only commands in separate threads

We don’t like:
We don’t mind (but could be a problem):
only commands in separate threads
We would love:
RxJava

Model
Plugin
Layout
+
Activity/
Fragment
Presenter
Use
Case
Model
Plugin
Use
Case Repository
Model
Plugin
Use
Case

Conclusions
photo by Daniel Sancho

When?
• If you expect 2+ devs working on the same
feature
• Unless you are sure the app is going to die
in a near future
• You know for sure you will change your
plugins

How?
1. Simple refactors
2. Model View Presenter
3. Hexagonal

How?
1. Simple refactors
2. Model View Presenter
3. Hexagonal
4. Clean Architecture

From Legacy to Hexagonal (An Unexpected Android Journey)

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