As presented in Droidcon Tel Aviv 2016: http://il.droidcon.com

1. Build An App With Blindfold
Britt Barak
Droidcon TLV
26.9.16

2. Britt Barak
Britt Barak
@BrittBarak
● Figure 8
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5. My First Startup

6. “As You Like It” / W. Shakespeare
‫״‬All the world’s a stage,
And all the men and women merely players;
They have their exits and their entrances,
And one man in his time plays many parts:‫״‬

7. His acts being seven ages. At first, the
infant,
Mewling and puking in the nurse’s arms.
Then the whining schoolboy, with his
satchel
And shining morning face, creeping like
snail
Unwillingly to school. And then the lover,
Sighing like furnace, with a woeful ballad
Made to his mistress’ eyebrow. Then a
soldier,
Full of strange oaths and bearded like the
pard,
Jealous in honor, sudden and quick in
quarrel,
Seeking the bubble reputation
Even in the cannon’s mouth. And then the
justice,
In fair round belly with good capon lined,
With eyes severe and beard of formal cut,
Full of wise saws and modern instances;
And so he plays his part. The sixth age
shifts
Into the lean and slippered pantaloon,
With spectacles on nose and pouch on side;
His youthful hose, well saved, a world too
wide
For his shrunk shank, and his big manly
voice,
Turning again toward childish treble, pipes
And whistles in his sound. Last scene of
all,
That ends this strange eventful history,
Is second childishness and mere oblivion,
Sans teeth, sans eyes, sans taste, sans
everything.

8. “exits and entrances”
The part can change
But there’s always a defined part.

9. File → New Project

10. New Startups
● Uncertainty
● Many changes
● Low on resources
○ Time
○ Developers
○ Money

11. We Want To Deliver Fast!
Premature optimizations are bad
1. Mess Grows
2. Structure Stays

12. Recipe
1. Big picture - who are the “players”?
2. Small use cases - what are the “parts”?
3. Choose POCs - order “exits and entrances”

13. High Level Structure
Presentation
Layer
Data LayerDomain Layer

14. High Level Structure
Presentation
Layer
● View
● ViewEntity
● Presenter
→ Framework
Data Layer
● Repository
● Entity
→ Java
Domain Layer
● Interactor
● Use case
→ Java

15. Example : Add Chat Feature To App

16. Big Picture - The Players
● Add chat feature to the app
● Chat between groups of members

17. Separation
App
Module
Chat
Module

18. Why New Module?
- Encapsulate implementation
- Easy to replace
- Easy to reuse

19. Structure:

20. Presentation Layer - App Module

21. Data Layer - Chat Module
let‘s talk about the data structure.

22. Firebase DB
- Easy.
- noSQL
- Flat
- Get data by reference
- ref/messages/chat_one_id

23. Don’t - Nest
{
"chats": {
"chatOneId": {
"title": "As You Like It",
"messages": {
"msg1Id": { "sender": "melancholyJaques", "message": "All world’s a stage." },
"msg2Id": { ... },
// a very long list of messages
}
},
"chatTwoId": { ... }
}
}

24. Do - Flat : Chats
{
"chats": {
"chatOneId": {
"title": "As You Like It"
},
"chatTwoId": { ... },
"chatThreeId": { ... }
}

25. Do - Flat : Members
{
"members": {
"chatOneId": {
"melancholyJaques": true,
"dukeSenior": true,
},
"chatTwoId": { ... },
"chatThreeId": { ... }
},

26. Do - Flat : Users
{
"users": {
"melancholyJaques": {
"name": Melancholy Jaques",
"photoId": "23h42",
"chats": {
"chatOneId": true,
"chatTwoId": true
}
},
...
},

27. Do - Flat : Messages
"messages": {
"chatOneId": {
"msg1Id": {
"sender": "melancholyJaques",
"message": "All world’s a stage.",
"timestamp": 1459361875337
},
"msg2Id": { ... },
// a very long list of messages
},
"chatTwoId": { ... },
}
}

28. On my code
Chat module: individual separate pieces:
- Chats Repository
- Members Repository
- Users Repository
- Messages Repository

29. Repository (Data Layer)
Part - provide and update data.
Encapsulates implementation.

30. public class UsersRepo implements IUsersRepository {
MyFirebaseDBClient firebaseClient;
@Override
public void getChatIDs(Callback callback) {
firebaseClient.fetchChats(callback);
}

31. public class UsersRepo implements IUsersRepository {
MyFirebaseDBClient firebaseClient;
MyCache cache;
@Override
public void getChatIDs(Callback callback) {
if (cache.hasChats()) {
callback.success(cache.getChatIDs());
} else {
firebaseClient.fetchChatIDs(callback);
}
}

32. public class UsersRepo implements IUsersRepository {
MyFirebaseDBClient firebaseClient;
MyCache cache;
ChatsLocalDB localDB;
@Override
public void getChatIDs(Callback callback) {
if (cache.hasChatIDs()) {
callback.success(cache.getChatIDs());
} else if (localDB.hasChatIDs()) {
callback.success(localDB.getChatIDs());
} else {
firebaseClient.fetchChatIDs(callback);
}
}

33. public class UsersRepo implements IUsersRepository {
MyApiClient apiClient;
MyCache cache;
ChatsLocalDB localDB;
@Override
public void getChatIDs(Callback callback) {
if (cache.hasChatIDs()) {
callback.success(cache.getChatIDs());
} else if (localDB.hasChatIDs()) {
callback.success(localDB.getChatIDs());
} else {
apiClient.fetchChatIDs(callback);
}
}

34. Recipe
1. Big picture - who are the “players”?
2. Small use cases - what are the “parts”?
3. Choose POCs - order “exits and entrances”

35. Domain layer - Use Cases
Use cases / interactors
What does the app do? What are its use cases?

36. Example: getChatsPreviewList (use case)

37. Get
user’s
chat IDs
Get
chat’s
info
Chats
Repo
Get
chats
preview
list
Chat
list
activity
Users
Repo
Get Chat Preview List

38. Get chats
preview
list
List<Chat>
List<String>
ChatRaw
Get Chat Preview List
List<ChatRaw>

39. Get Chat Preview List
public class GetChatPreviewListImpl implements GetChatsPreviewList {
public void execute(final Callback<List<Chat>> callback) {
usersRepo.getChatIDs(new Callback<List<String>>() {
@Override
public void success(List<String> chatIDs) {
chatsRepo.getChats(new Callback<List<RawChat>>() {
@Override
public void success(List<RawChat> rawChats) {
List<Chat> chats = proccessChats(rawChats);
callback.success(chats);
}
});
}
});

40. Get chats
preview
list
Get chat
members
Get chat
messags
….
App Module Will Ask For More
Chat
list
activity

41. Recipe
1. Big picture - who are the “players”?
2. Small use cases - what are the “parts”?
3. Choose POCs - order “exits and entrances”

42. Choose POC
- Play the App Module Part:
- Forget the chat implementation!
- ChatClient - POC class

43. Chat Client
Get chats
preview
list
Get chat
members
Get chat
messags
….
Choose POC
App
Module

44. Get Chat Preview List
Chat
list
activity
Chat
Client
Users
Repo
Chats
Repo
userId chatIds

45. Demand
On chats preview list:
show last message

46. Get Chat Preview List 2
Too messy. Too many listeners and threads. Too much time.
Chat
Client
Users
Repo
Chat
list
activity
Chats
Repo
userId chatIds
Msgs
Repo
Get
chats
preview
list

47. Get Chat Preview List 3
Add data straight to chat Info node
"chats": {
"chatOneId": {
"title": "As You Like It"
"lastMessage": "All world’s a stage"
},
"chatTwoId": { ... },
"chatThreeId": { ... }
},

48. Get Chat Preview List 3
Too messy. Too many listeners and threads. Too much time.
Chat
Client
Users
Repo
Chat
list
activity
Chats
Repo
userId chatIdsGet
chats
preview
list

49. But now:
more work when sending a message

50. Send : Before
Chat
activity
Chat
Client
Msgs
Repo
Send

51. Send : After
Chat
activity
Chat
Client
Msgs
Repo
Send
Chats
Repo

52. Demand
Message visibility per user.
“Last message”
isn’t general anymore.

53. Structure - Message
"message1": {
...
"visibleTo": {
"userId1": true,
"userId2": true
},
}

54. Structure - Personal Chat Info
Chats
General
Info
Personal
Info
title
Last
msg

55. Personal Chat Info Node
{
"personalInfo": {
"melancholyJaques": {
"lastMessage": All world’s a stage",
"timestamp": 1459361875337
},
...
},

56. Get Chat Preview List 4
Too messy. Too many listeners and threads. Too much time.
Chat
Client
Users
Repo
Chat
list
activity
userId chatIdsGet
chats
preview
list
personal
Info
Repo
general
Info
Repo

57. Send : Update Per User
App
Module
Chat
Client
Msgs
Repo
userId chatIds
personal
Info
Repo
Send
Is visible?

58. But I have many recipients….
Takes long to update each user repo...

59. Send :
Send
Message
Repo
FCM

60. Receive :
Send Receive
Personal
Info
Repo
Message
Repo
FCM

61. Give the part to a differenet Player

62. Sum Up
- Small defined use cases:
- Easy to maintain
- Easy to change
- Easy to test
- Mix and match
- “Play the part” → create POC class
- Encapsulate implementation
- Organize code
- Be mindful to what needs a change

63. Example changing the part

65. FCM Usages
- Notify user
- Update DB
- Update UI
- Fetch new data
- Start service
- ……...

66. How Does It Work?
public class MyFCMService extends FirebaseMessagingService {
@Override
public void onMessageReceived(RemoteMessage remoteMessage) {
//...
}
}

67. Remote Message Part
Notify about an event.

68. FCM Handling
Type per message
RemoteMessage
Data
….
< “type” , “new_chat_message” >
….

69. FCM Handling
public class MyFCMService extends FirebaseMessagingService {
@Override
public void onMessageReceived(RemoteMessage remoteMessage) {
String type = data.get(StaticKeys.KEY_TYPE);
switch (type) {
//....
}
}
}

70. It Worked Great...
We added up more and more events…..
- New chat message
- New member added
- Member removed
- New data available
- ………………..

71. …for some time :-/
- Too many event types
- Too complex code
- Hard to change
- Hard to combine
- Sometimes one usecase represented multiple event types and forced few fcm
messages
- The ugly switch-case...

72. Demand
- Easily support new types
- Change remotely

73. Wait….
Take a step back.
What did we mean to do?
1. Notifying users
2. Update data / ui
3. Update DB

74. Remote Message Part
Notify an event.
Notify about stuff that need to be done.

75. Handle By Data Attributes
RemoteMessage
Data
….
<“notify” , “true” >
<“title” , “New Message” >
<“icon” , “ic_chat” >
<“click_action”,
“com.figure8.app.action.OPEN_CHAT”>
<“refresh_members”, chat_id>
….

76. Handle By Data Attributes
Messaging
Service
Notif
Producer
Data
Refresher
DB
Updater
Remote
Message
Remote
Message

77. Pros
- Flexible
- Update remotely
- Test:
- Test the data producer
- Test the data handler

78. What Did We Do?
Gave the component a different part.

79. “exits and entrances”
The part can change
But there’s always a defined part.

80. Questions?

81. Thank you :)