Coroutines and Flow integration with Android Architecture Components

In just two years, Andorid development has radically evolved: Google I/O 2017 marked the introduction of Kotlin as a supported language in the platform and just two years later, Google announced that Android Development will be Kotlin-first.

In this talk, we'll learn together what Coroutines are and how they're changing the way Android Developers are writing code. Then, we will explore the world of Architecture Components, learning how ViewModel, LiveData, WorkManager and Room can integrate with Kotlin language features like Coroutines and Flow, making the development of an app architecture easier than ever. We'll also have some `fun` converting old callbacks in the Andoird framework to Kotlin suspend functions!

Transcript

1. Coroutines and Flow with Architecture Components Paolo Rotolo @paolorotolo
2. Long running tasks • Network requests • Database operations • Image processing • ...
3. Execute on a non-UI thread
4. Execute on a non-UI thread Get informed when the task is done
5. Execute on a non-UI thread Get informed when the task is done Android solutions • AsyncTask • RxJava • Thread / HandlerThread / Executor with callbacks
6. Execute on a non-UI thread Get informed when the task is done Android solutions • AsyncTask • RxJava • Thread / HandlerThread / Executor with callbacks
7. Execute on a non-UI thread Get informed when the task is done Android solutions • AsyncTask • RxJava • Thread / HandlerThread / Executor with callbacks
8. Execute on a non-UI thread Get informed when the task is done callbacks!!! • AsyncTask • RxJava • Thread / HandlerThread / Executor with Android solutions
9. • AsyncTask • RxJava • Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions
10. • AsyncTask • RxJava • Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions Deprecated this month!
18. • AsyncTask • RxJava • Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions Deprecated this month!
19. • AsyncTask • RxJava • Thread / HandlerThread / Executor with Execute on a non-UI thread Get informed when the task is done callbacks!!!1 Android solutions Deprecated this month! Need to handle cancellation
20. Kotlin Coroutines
21. Kotlin Coroutines simple state machine
22. Threads and callbacks fun login(name, pass) { val thread = Thread(Runnable() -> { requestLogin(name, pass) { result -> show(result) } } thread.start() }
23. Threads and callbacks fun login(name, pass) { val thread = Thread(Runnable() -> { requestLogin(name, pass) { result -> Handler(Looper.getMainLooper()) { show(result) } } }
24. Threads and callbacks fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }
25. onDraw onDraw onDraw requestLogin UI Thread fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }
26. onDraw onDraw onDraw requestLogin UI Thread fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }
27. onDraw onDraw onDraw requestLogin UI Thread show onDraw fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }
28. onDraw onDraw onDraw requestLogin UI Thread show onDraw fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } onDraw onDraw onDraw
29. Coroutine = suspendable computation onDraw onDraw onDraw requestLogin UI Thread show onDraw onDraw onDraw onDraw
30. When all of the coroutines on the main thread are suspended, the main thread is free to do other work.
31. Kotlin Coroutines simple state machine
32. Kotlin Coroutines simple state machine suspend keyword
33. Kotlin Coroutines simple state machine suspend keyword dispatchers
34. Dispatchers.Main • Main thread • Use it for: UI operations
35. Dispatchers.Default • Common pool of shared background threads • Use it for: computing-intensive coroutines Dispatchers.Main • Main thread • Use it for: UI operations
36. Dispatchers.Default • Common pool of shared background threads • Use it for: computing-intensive coroutines Dispatchers.IO • Shared pool of on-demand created threads • Use it for: IO-intensive blocking operations Dispatchers.Main • Main thread • Use it for: UI operations
37. Dispatchers.Default • Common pool of shared background threads • Use it for: computing-intensive coroutines Dispatchers.IO • Shared pool of on-demand created threads • Use it for: IO-intensive blocking operations Dispatchers.Main • Main thread • Use it for: UI operations Common thread pools!
38. Dispatchers.Default • Common pool of shared background threads • Use it for: computing-intensive coroutines Dispatchers.IO • Shared pool of on-demand created threads • Use it for: IO-intensive blocking operations Dispatchers.Main • Main thread • Use it for: UI operations Common thread pools! Easy to switch dispatchers!
40. Used for example by libraries
41. Kotlin Coroutines simple state machine suspend keyword dispatchers
42. Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency
43. Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency (scope)
44. Kotlin Coroutines Hello World
45. Kotlin Coroutines World Hello
46. // prints Hello, World!
47. Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency
48. Kotlin Coroutines simple state machine suspend keyword dispatchers structured concurrency <3 Andorid
49. Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status
50. fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } requestLogin Thread show Suspension point
51. suspend fun requestLogin( name: String, pass: String ): Result {...}
52. Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status
53. Login button pressed Launch coroutine requestLogin Show login status val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job)
54. Login button pressed Launch coroutine requestLogin Show login status val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job) fun login(username: String, pass: String ) = uiScope.launch { val result = requestLogin(name, pass) show(result) }
55. Login button pressed Launch coroutine requestLogin Show login status val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job) fun login(username: String, pass: String ) = uiScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) }
56. Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status Activity destroyed
57. Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status Activity destroyed Coroutine leak
58. Coroutines + ViewModel
59. Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status ViewModel
61. Login button pressed Launch coroutine requestLogin Show login status ViewModel fun onCleared() { super.onCleared() job.cancel() }
62. class MyViewModel: ViewModel() { val viewModelJob = Job() val uiScope = CoroutineScope(Dispatchers.Main+viewModelJob) fun login( username: String, pass: String ) = uiScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) } fun onCleared() { super.onCleared() viewModelJob.cancel() } }
63. class MyViewModel: ViewModel() { val viewModelJob = Job() val uiScope = CoroutineScope(Dispatchers.Main+viewModelJob) fun login( username: String, pass: String ) = uiScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) } fun onCleared() { super.onCleared() viewModelJob.cancel() } } lifecycle-viewmodel-ktx
64. class MyViewModel: ViewModel() { fun login( username: String, pass: String ) = viewModelScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) } }
65. suspend does not mean background
66. class MyViewModel: ViewModel() { fun login( username: String, pass: String ) = viewModelScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) } }
67. Coroutines + Lifecycle
68. Coroutines + Lifecycle viewmodel.viewModelScope
69. Coroutines + Lifecycle activity.lifecycleScope viewmodel.viewModelScope
70. Coroutines + Lifecycle activity.lifecycleScope fragment.lifecycleScope fragment.viewLifecycleOwner viewmodel.viewModelScope
71. Coroutines + Lifecycle Examples
73. Coroutines + Lifecycle
74. Coroutines + Lifecycle React to Lifecycle.State
77. Coroutines + LiveData
78. Coroutines + LiveData getUser Example
81. Coroutines + LiveData LiveData Builder
87. Coroutines + LiveData Builder Examples
90. Coroutines + LiveData getUser Example
93. Coroutines + LiveData LiveData Builder + other LiveData!
100. Coroutines + Room
101. Coroutines + Room Suspending DAO functions
103. Coroutines + Room Behind the scenes
105. Runs on IO threads
106. Runs on IO threads IO-Thread-1
107. Runs on IO threads IO-Thread-1 IO-Thread-2
108. Android SQLite transactions are thread confined
109. Runs on IO threads IO-Thread-1 IO-Thread-2
110. Runs on IO threads IO-Thread-1 IO-Thread-2 Will block until transaction in Io-Thread-1 ends
111. Runs on IO threads IO-Thread-1 IO-Thread-2 Will block until transaction in Io-Thread-1 ends DEADLOCK!
113. Coroutines + Room Behind the scenes Coroutines executor
117. Immediately execute the callable
118. Immediately execute the callable Use Room dispatchers
119. Immediately execute the callable Use Room dispatchers Free main-safety!
120. Coroutines + WorkManager
121. Coroutines + WorkManager Types of background work
123. Coroutines Coroutines
124. Coroutines Coroutines Foregroun dService
125. Coroutines Coroutines Foregroun dService WorkManager
126. Coroutines + WorkManager Simple Example
131. Defaults to Dispatcher.Default
133. Coroutines + WorkManager WorkManager -> ForegroundService
136. suspendCancellableCoroutine Make callbacks Great again
145. suspendCancellableCoroutine Structured Concurrency
147. Coroutines + Flows
148. Coroutines + Flows Cold stream of data
150. Coroutines + Flow Flow builder
153. Coroutines + Flow Example: Firebase Realtime
163. Questions? Paolo Rotolo @paolorotolo
164. Thank you! Paolo Rotolo @paolorotolo