A Separation of Concerns Clean Architecture on Android

Transcription

1 A Separation of Concerns Clean Architecture on Android Kamal Kamal Mohamed Android Developer, //TODO Find Better Outware Mobile Ryan Hodgman Official Despiser of Utils Outware Mobile 18/09/ YOW Connected 2015

2 Why are we here? To share with you our journey in applying Clean Architecture to an Android project...and get some valuable feedback

3 Premise Our own interpretation Multiple possible implementations Under development Iterating on it on a day to day basis Not a silver bullet Best suited for medium-big projects

4

5 What are our goals as developers? Maintainable Easy to refactor on volatile projects

6 What are our goals as developers? Maintainable Easy to refactor on volatile projects Testable Be confident that the code is reliable

7 What are our goals as developers? Maintainable Easy to refactor on volatile projects Testable Be confident that the code is reliable Scalable Can increase scope without requiring a rework

8 What are our goals as developers? Maintainable Easy to refactor on volatile projects Testable Be confident that the code is reliable Scalable Can increase scope without requiring a rework Readable Reduce the difficulty of future development efforts

9 Introduction to Clean

10 What is Clean Architecture?

11 Robert Martin s original depiction of Clean Architecture 8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html

12 The Dependency Rule Source code dependencies can only point inwards

13 How many layers? (The answer is three)

14 Separation of Concerns Presentation Logic Defines how to display visual information to the user Examples: Organize screen layout Format text Enable user input

15 Separation of Concerns Business Logic Implements the business requirements of the application Examples: Verify user authorization Choose data to be displayed Determine if additional user input is required

16 Separation of Concerns Data Logic Stores and retrieves data to achieve the business requirements Examples: Make an API call Query a local database Access the local filesystem

17 Architectural Diagram

18 Architectural Diagram Image Source: Lucasfilm Ltd. All Rights Reserved

19 Domain Layer

20 Domain Layer

21 Entity Represents a business object that concerns the application Least likely to change when shifting requirements

22 Entity Represents a business object that concerns the application Least likely to change when shifting requirements Responsibilities Model the relationships with real-world objects / concepts Encapsulate the properties required by the application s business logic

23 Entity Represents a business object that concerns the application Least likely to change when shifting requirements Responsibilities Interactions Model the relationships with real-world objects / concepts May be used directly by all layers of the application Encapsulate the properties required by the application s business logic Likely that they may be mapped from data sources or to presentable view models

24 Entity

25 Entity Properties

26 Entity Entity-specific logic

27 Use Case Contains the business logic related to a specific use case Can be run and canceled

28 Use Case Contains the business logic related to a specific use case Can be run and canceled Responsibilities Execute a piece of business logic Define a Callback to provide results Inform the Callback of the result Interact with the data layer

29 Use Case Contains the business logic related to a specific use case Can be run and canceled Responsibilities Execute a piece of business logic Define a Callback to provide results Inform the Callback of the result Interactions Use Case Implements Notifies Uses Interact with the data layer Repository Callback Use Case Callback Repository

30 Use Case

31 Use Case One or more Repository objects

32 Use Case May be run and cancelled

33 Use Case Contains business logic

34 Use Case Defines interactions

35 Repository Asynchronous interface to abstract data access to a specific set of data from the data layer

36 Repository Asynchronous interface to abstract data access to a specific set of data from the data layer Responsibilities Provide methods to store and retrieve data of a specific type Define Callback interfaces to return the results of each operation

37 Repository Asynchronous interface to abstract data access to a specific set of data from the data layer Responsibilities Interactions Repository Provide methods to store and retrieve data of a specific type Uses Define Callback interfaces to return the results of each operation Use Case Implements Data Manager

38 Repository

39 Repository Asynchronous

40 Repository Callback definition

41 A Brief Note on Test-Driven-Development

42 Presentation Layer

43 Presentation Layer

44 Model-View-Presenter Implements View Surface Activity Fragment Presentation Uses View Presenter Domain Uses Uses

45 Presenter Implements presentation logic by directing UI changes and handling user input

46 Presenter Implements presentation logic by directing UI changes and handling user input Responsibilities Direct UI changes Handle user triggered UI events Create and trigger Use Case objects Define a View Surface interface

47 Presenter Implements presentation logic by directing UI changes and handling user input Responsibilities Direct UI changes Handle user triggered UI events Create and trigger Use Case objects Interactions Presenter Implements Uses Triggers Define a View Surface interface Use Case Callback View Surface Use Case

48 Presenter

49 Presenter Systems Surfaces and Use Cases

50 Presenter Lifecycle events

51 Presenter UI event management

52 View Surface Abstracts away the implementation of the UI logic, and is typically implemented by a View, Activity or Fragment

53 View Surface Abstracts away the implementation of the UI logic, and is typically implemented by a View, Activity or Fragment Responsibilities Screen layout Animations / transitions Propagate UI events to the Presenter Navigation

54 View Surface Abstracts away the implementation of the UI logic, and is typically implemented by a View, Activity or Fragment Responsibilities Screen layout Animations / transitions Propagate UI events to the Presenter Navigation Interactions Activity Implements Presenter View Surface Informs Presenter

55 View Surface

56 View Surface Navigation

57 View Surface UI information

58 View Surface UI state

59 System Surface Abstracts away the implementation of various system functionalities

60 System Surface Abstracts away the implementation of various system functionalities Responsibilities Provide functionality specific to the OS / device Gracefully fail in the event of missing functionality

61 System Surface Abstracts away the implementation of various system functionalities Responsibilities Provide functionality specific to the OS / device Gracefully fail in the event of missing functionality Interactions System Surface Used by Presenter

62 System Surface

63 System Surface Android system dependencies

64 System Surface System-specific implementation

65 Data Layer

66 Data Layer

67 Data Manager Implements a single Repository interface to handle all the data sources required for a specific set of data

68 Data Manager Implements a single Repository interface to handle all the data sources required for a specific set of data Responsibilities Provide access to a specific set of data Make request on a data source in the form of a Client Handle a cache when required

69 Data Manager Implements a single Repository interface to handle all the data sources required for a specific set of data Responsibilities Interactions Data Manager Provide access to a specific set of data Implements Notifies Uses Make request on a data source in the form of a Client Repository Callback Repository Handle a cache when required Client

70 Client Encapsulates a particular source of data and exposes an abstracted interface to the Data Managers

71 Client Encapsulates a particular source of data and exposes an abstracted interface to the Data Managers Responsibilities Make Database queries Manage an API connection Access Local Storage Map data results to domain Entities

72 Client Encapsulates a particular source of data and exposes an abstracted interface to the Data Managers Responsibilities Interactions Client Make Database queries Handles Manage an API connection Access Local Storage Map data results to domain Entities Used by Uses Data Manager Data Source Mapper

73 Mapper Converts a data object (API or DB response) to a domain Entity

74 Mapper Converts a data object (API or DB response) to a domain Entity Responsibilities Transform data into domain-convenient Entities

75 Mapper Converts a data object (API or DB response) to a domain Entity Responsibilities Transform data into domain-convenient Entities Interactions Data Object Mapper Entity

76 Conclusions

77 Pros Workflow improvements Possibility to work on separate layers in parallel Code readability No more line Activity classes Testability Isolated business logic

78 Cons Hierarchy implementation Implementing a feature requires working across all of the layers Developer onboarding Increased ramp-up time for new developers Interfaces Interfaces, interfaces,...

79 Further thoughts Dependency injection Dagger 2! Can help a lot with keeping the layers clean

80 Further thoughts Dependency injection Dagger 2! Can help a lot with keeping the layers clean Thread management Where should we split tasks onto a worker thread?

81 Further thoughts Dependency injection Dagger 2! Can help a lot with keeping the layers clean Thread management Where should we split tasks onto a worker thread? Functional programming RxJava! Helps to reduce callbacks and make flows clearer

82 Further thoughts Dependency injection Dagger 2! Can help a lot with keeping the layers clean Thread management Where should we split tasks onto a worker thread? Functional programming RxJava! Helps to reduce callbacks and make flows clearer User narratives May be useful to model a stateful user flow through the application

83 Next thing you can do! Consider the separation between data, domain, and presentation logic in one of your projects

84 References The Clean Architecture [Uncle Bob] Architecting Android The clean way? [Fernando Cejas] Sample Project [Ryan and Kamal]

85 Contact details Kamal Kamal Mohamed Ryan Hodgman