How to reuse code in Android and how we do it in Peewah to develop mobile applications for events natively

1. Keep calm and write
reusable code in Android
Juan Camilo Sacanamboy
Co-founder and mobile developer at Peewah
http://peewah.co

2. Content
1. Code reusability
2. The most used technique
3. Code reusability in Android

3. Code reusability

4. History
● 1968: Douglas Mcllroy of Bell Laboratories proposed basing the software
industry on reusable components
● Write once and use it in many projects
● Not only reuse the code but also test suites, designs, documentation, and so
on.
● Improve the code duplication caused by copy & paste programming

5. Types of reuse
Concerning motivation and driving factors, reuse can be:
● Opportunistic
● Planned
Reuse can be categorized further:
● Internal reuse
● External reuse
Concerning form or structure of reuse, code can be:
● Referenced
● Forked

6. Examples
● Software libraries
● Design patterns
● Higher-order function
● Retrocomputing
● Components
● Outside of computers

7. Reusable software? Just don’t write generic code
● “It’s a common mistake to make software too generic”
● “Maximizing genericity complicates use”
● “Reusable software requires loose coupling and strong cohesion”
● Pitfalls
○ Abstraction layers everywhere
○ Excessive use of inheritance
Reference: http://josdejong.com/blog/2015/01/06/code-reuse/

8. 2. The most used technique

9. Yes! It’s the copy & paste programming

10. The Last Line Effect
● 84 code fragments
○ 41 contain mistakes somewhere in the middle
○ 43 contain mistakes in the last copied code block
Reference: http://www.viva64.com/en/b/0260/ - Andrey Karpov
Figure 1. A rough diagram of mistake distribution in five
homogeneous code blocks.
The probability of making
a mistake in the last
pasted block of code is 4
times higher than in any
other block.

11. Examples
Reference: http://www.viva64.com/en/b/0260/ - Andrey Karpov
Source Engine SDK
Chromium

12. Examples
Reference: http://www.viva64.com/en/b/0260/ - Andrey Karpov
ReactOS
Multi Theft Auto

13. Examples
Reference: http://www.viva64.com/en/b/0260/ - Andrey Karpov
Source Engine SDK

14. Code reusability in Android

15. Activities
“An application component that provides
a screen with which users can interact
in order to do something…each activity
is given a window in which to draw its
user interface.”
Reference: http://developer.android.com/guide/components/activities.html

16. Fragments
Added in API level 11 (Android 3.0)
“A modular section of an activity,
which has its own lifecycle, receives its
own input events, and which you can
add or remove while the activity is
running”
Reference: http://developer.android.com/guide/components/activities.html

17. Java Archive (jar) vs Android Archive (aar)
● jar: Java classes
● aar: drawables, layouts, assets, styles, Android Manifest, libs, and so on
In Android Studio (Gradle build) you can use library in 3 ways
1. Library is a separate module in a project (multi-module project)
2. Library can be stored locally in the project (typically in libs folder)
3. Library can be deployed into a repository (Maven, Ivy Repository, JCenter)
Reference: http://stackoverflow.com/questions/29450709/how-to-create-reusable-activities-in-android

18. Multi-module project
● Multiple APKs with common library
with a multi-module project (some
modules are libraries, some
modules are applications.
● Problem: many apps in the same
project.
dependencies {
project(":library-module")
}
Reference: http://stackoverflow.com/questions/29450709/how-to-create-reusable-activities-in-android

19. Locally stored library
● Compile classes in a jar file
● Problem: updating local jar every
time you update the library
Reference: http://stackoverflow.com/questions/29450709/how-to-create-reusable-activities-in-android
dependencies {
compile files('libs/some_library.jar')
}

20. Deployed libraries
● The best way to use libraries in a
project
● You need a server (unless you
create an open source, in that case
you can use Maven Center or
jCenter)
● You can use a local repository, but
that’s difficult when you’re working
with other developers
dependencies {
compile 'com.google.code.gson:gson:2.2.4'
}
Reference: http://stackoverflow.com/questions/29450709/how-to-create-reusable-activities-in-android

22. Peewah’s product:
Native apps for events
● Home
● Schedule (by day and topic)
● Twitter feed
● Gallery
● Photobooth
● Maps
● Phone numbers

23. Peewah’s architecture (native apps for events)

24. Characteristics of our architecture
● The library is an Android Module
● Each menu is a fragment and it’s decoupled from the others
● Each menu has parameters to configure it
● If there are dependencies between fragments we use a publisher/subscriber
mechanism (Otto)
● The library don’t depend of the technology used in the backend

25. The library is an Android Module

26. Each menu is a fragment and it’s decoupled

27. Each menu has parameters to configure it

28. Publisher/subscriber mechanism for dependencies
MainActivity
notifies two
type of events
to the
subscribers:
Events and
Milestones
The fragment (subscriber) receives the
information
The fragment subscribes to the Activity
(publisher)

29. Don’t depend of the technology used in the backend

30. Before our library
● Average development time: 2 months
● Many classes, activities, fragments, layouts (>60)

31. After our library
● Average development time: 1 week
● One class in the app (MainActivity)
Add menus in the Main
Activiy

32. After our library
Add Home Menu to the Main Activity with the Library (3 lines of code)

33. Questions
@csacanam - camilo@peewah.co