The document discusses best practices for designing Android applications that support offline functionality, highlighting the benefits such as improved user experience and reduced network usage. It covers various architectural patterns, data storage options, and the use of tools like Retrofit and Realm for data management. Key takeaways emphasize the importance of encapsulating data access and ensuring applications remain functional without a constant internet connection.

1. Painless Persistence
on Android
Christian Melchior
@chrmelchior
cm@realm.io

5. Why design for offline?
• A better USER EXPERIENCE!
• You always have something to show the user
• Reduce network requests and data transferred
• Saves battery

6. Designing for Offline

7. Offline architecture
MVVM
MVP
MVC
VIPER
Flux
Clean
Architecture
?
?
? ?
?
?
?
?
?
?
?
?
??
??

8. They all have a model
MVVM
MVP
MVC
VIPER
Flux
Clean
Architecture
ModelView
getData()
data

9. You’re doing it wrong!
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Setup initial views
setContentView(R.layout.activity_main);
// Load data and show it
Retrofit retrofit = new Retrofit.Builder()
.addConverterFactory(JacksonConverterFactory.create())
.baseUrl("http://api.nytimes.com/")
.build();
service = retrofit.create(NYTimesService.class);
service.topStories("home", "my-key").enqueue(new Callback<NYTimesResponse<List<NYTimesStory>>>() {
@Override
public void onResponse(Response<NYTimesResponse<List<NYTimesStory>>> response, Retrofit retrofit) {
showList(response);
}
@Override
public void onFailure(Throwable t) {
showError(t);
}
});
}

10. You’re doing it right!
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Setup initial views
setContentView(R.layout.activity_main);
// Load data and show it
Model model = ((MyApplication) getApplicationContext()).getModel();
model.getTopStories(new Observer() {
@Override
public void update(Observable observable, NYTimesResponse<List<NYTimesStory>> data) {
showList(data);
}
});
}

11. Encapsulate data
ModelView
Cache
Database
Network

12. Repository pattern
ModelView
Cache
Database
Network
Repository
Business rules
Creating/
fetching data

13. Repository pattern
• Repository only has CRUD methods:
• Create()
• Read()
• Update()
• Delete()
• Model and Repository can be tested separately.

14. Designing for offline
Repository… DatastoregetData()
Observable<Data>()
Network
Update?
Save

15. Designing for offline
• Encapsulate data access
• The datastore is single-source-of-truth
• Everything is asynchronous
• Observer pattern
• RxJava
• EventBus
• Testing becomes easier

16. Persisting data

17. File system
• Define hierarchy using folders
• No help from the framework
• Use cases: Images, JSON blobs

18. File system
// App internal files
context.getFilesDir();
context.getCacheDir();
// App external files
context.getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS);
context.getExternalCacheDir();
// SD Card
Environment.getExternalStorageDirectory();

19. SharedPreferences
• Key-value store
• Simple XML file
• Use cases: Settings, Key/Value data
• Simple API’s and easy to use

20. SharedPreferences
// Save data
SharedPreferences pref = getPreferences(MODE_PRIVATE);
SharedPreferences.Editor editor = pref.edit();
editor.putBoolean("key", true);
editor.commit();
// Read data
boolean data = pref.getBoolean("key", false);

21. Databases
• Use cases: Structured data sets
• Advanced composing and query capabilities
• Complex API’s

22. SQLite vs. the World
• SQLite (Relational)
• Realm (Object store)
• Firebase (Document oriented)
• Couchbase Lite (Document oriented)
• Parse (Document oriented)

23. The Relational Model

24. Relational data

25. Relational data

26. BCNF
Relational data

27. Relational data

28. m:n?
Relational data

29. Relational data

30. SELECT owner.name, dog.name, city.name
FROM owner
INNER JOIN dog ON owner.dog_id = dog.id
INNER JOIN city ON owner.city_id = city.id
WHERE owner.name = 'Frank'
SQLite

31. String query = "SELECT " + Owner.NAME + ", " + Dog.NAME + ", " + City.NAME
+ " FROM " + Owner.TABLE_NAME
+ " INNER JOIN " + Dog.TABLE_NAME + " ON " + Owner.DOG_ID + " = " + Dog.ID
+ " INNER JOIN " + City.TABLE_NAME + " ON " + Owner.CITY_ID + " = " + City.ID
+ " WHERE " + Owner.NAME = "'" + escape(queryName) + "'";
SQLite

33. “Lets use an ORM”
Abstract the problem away

34. –Joel Spolsky
“All non-trivial abstractions, to some degree,
are leaky.”

35. Solved problem?
• ActiveRecord
• Androrm
• Blurb
• Cupboard
• DBFlow
• DBQuery
• DBTools
• EasyliteOrm
• GreenDAO
• Ollie
• Orman
• OrmLite
• Persistence
• RushORM
• Shillelagh
• Sprinkles
• SquiDB
• SugarORM

36. Realm?

37. Object Store
A
B C
D E F
G
VS

38. x
z
y
x y z
SELECT table1.x, table2.y, table3.z
FROM table1
INNER JOIN table2 ON table1.table2_id = table1.id
INNER JOIN table3 ON table1.table3_id = table3.id
References in SQL

39. A
B C
D E F
G
Realm.getA().getC().getF()
Object Store references

40. Zero-copy
Person
{
• name
=
Tommy
• age
=
8
• dog
=
{
• name
=
Lassie
}
}
Person
{
• name
=
Tommy
• age
=
8
• dog
=
{
• name
=
Lassie
}
}
Person
{
• name
=
Tommy
• age
=
8
• dog
=
{
• name
=
Lassie
}
}
PersonProxy
{
• name
• age
• dog
}
PersonProxy
{
• name
• age
• dog
}
Person
{
• name
=
Tommy
• age
=
8
• dog
=
{
• name
=
Lassie
}
}
Realm
ORM Realm
SQLite

41. Benchmarks
http://static.realm.io/downloads/java/android-benchmark.zip
1.09%
2.26%
3.79%
4.55%
22.85%
13.37%
1% 1% 1% 1% 1% 1%
0%
5%
10%
15%
20%
25%
BatchWrite% SimpleWrite% SimpleQuery% FullScan% Sum% Count%
Speedup&vs.&SQLite&
Tests&/&1000&objects&
Realm%
SQLite%

42. SQLite vs. Realm
• Part of Android
• Relational data model
• Based on SQL
• Public Domain
• One of the most tested pieces of software
• Need to map between SQL and Java
objects (manually or ORM).
• Foreign collections is an unsolvable
problem.
• Complex API’s
• Objects all the way down
• Zero copy architecture
• Cross-platform
• Supports encryption out of the box
• Open source*
• Custom query language
• Will add ~2500 methods + 800 kB of native
code.
• Still in beta

43. “Talk is cheap. Show
me the code.”
–Linus Torvalds

44. Adding Realm
// ./build.gradle
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:2.0.0-alpha1'
classpath 'io.realm:realm-gradle-plugin:0.86.0'
}
}
// ./app/build.gradle
apply plugin: 'com.android.application'
apply plugin: 'realm'

45. Models and Schema
public class Person extends RealmObject {
private String name;
private int age;
private Dog dog;
private RealmList<Cat> cats;
// Autogenerated getters/setters
}
public class Cat extends RealmObject {
private String name;
// Autogenerated getters/setters
}
public class Dog extends RealmObject {
private String name;
// Autogenerated getters/setters
}

46. Getting an Realm instance
// Default configuration. Schema is automatically detected
RealmConfiguration config = new RealmConfiguration.Builder(context).build();
Realm.setDefaultConfiguration(config);
Realm realm = Realm.getDefaultInstance();

47. Create objects - Realm
// Create and set persisted objects
realm.beginTransaction();
Person person = realm.createObject(Person.class);
person.setName("Young Person");
person.setAge(14);
realm.commitTransaction();
// Copy java objects
Person person = new Person();
person.setName("Young Person");
person.setAge(14);
realm.beginTransaction();
realm.copyToRealm(person);
realm.commitTransaction();
• Extend RealmObject
• POJO: Plain Old Java Object

48. Transactions - Realm
// Simple writes
realm.beginTransaction();
// ...
realm.commitTransaction();
// Automatically handle begin/commit/cancel
realm.executeTransaction(new Realm.Transaction() {
@Override
public void execute(Realm realm) {
// ...
}
});

49. Queries
RealmResults<Person> results = realm.where(Person.class)
.equalTo("age", 99)
.findAll();
RealmResults<Person> results = realm.where(Person.class)
.equalTo("cats.name", “Tiger")
.findAll();
RealmResults<Person> results = realm.where(Person.class)
.beginsWith("name", “John")
.findAllAsync();
results.addChangeListener(new RealmChangeListener() {
@Override
public void onChange() {
showResults(results);
}
});
• Fluent queries
• Semi-typesafe
• Easy async
• Always up-to-date

50. Network data
// Use Retrofit to parse objects
Retrofit retrofit = new Retrofit.Builder()
.addConverterFactory(JacksonConverterFactory.create())
.baseUrl("http://api.nytimes.com/")
.build();
MyRestApi service = retrofit.create(MyRestApi.class);
final Data data = service.getData();
// Copy all data into Realm
realm.executeTransaction(new Realm.Transaction() {
@Override
public void execute(Realm realm) {
realm.copyToRealmOrUpdate(data);
}
});

51. RxJava (Realm)
Observable<Realm> observableRealm = realm.asObservable();
Observable<RealmResults<Person>> results = realm.where(Person.class)
.beginsWith("name", “John")
.findAllAsync()
.asObservable();
Observable<Person> results = realm.where(Person.class).findFirst().asObservable();
Observable<RealmQuery> results = realm.where(Person.class).asObservable();

52. Example
https://github.com/realm/realm-java/tree/cm/offline-
newsreader/examples/newsreaderExample

53. Take aways
• Not everyone is on Wifi or 4G networks
• Encapsulate data access
• Designing for offline gives a a better USER
EXPERIENCE!

54. Resources
• Repository Pattern: http://martinfowler.com/eaaCatalog/
repository.html
• Design for offline: https://plus.google.com/
+AndroidDevelopers/posts/3C4GPowmWLb
• MVP example: https://www.code-labs.io/codelabs/
android-testing/#0
• Optimizing network requests: https://www.youtube.com/
playlist?list=PLWz5rJ2EKKc9CBxr3BVjPTPoDPLdPIFCE
• Realm : https://realm.io/docs/java/latest/

55. Questions?
@chrmelchior
cm@realm.io
We are hiring
https://realm.io/jobs/