Using_Kotlin_Coroutines.pdf

Transcript

1. Using Kotlin Coroutines In your Android App Heri Sulistiyanto https://github.com/herisulistiyanto https://medium.com/@heri.sulis
2. Long running tasks • Network requests • Database operations • Image processing • ...
3. Challenge 1: Execute on a non-UI thread Challenge 2: Get informed when the task is done
4. Android solutions • AsyncTask • Loaders (deprecated in Android P) • RxJava • Thread / HandlerThread / Executor with callbacks
5. Threads and callbacks fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } }
6. fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } onDraw onDraw onDraw requestLogin UI Thread
7. fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } onDraw onDraw onDraw requestLogin UI Thread onDraw process is blocked
8. fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } onDraw onDraw onDraw requestLogin UI Thread show onDraw onDraw process is blocked
9. fun login(name, pass) { requestLogin(name, pass) { result -> show(result) } } onDraw onDraw onDraw requestLogin UI Thread show onDraw onDraw onDraw onDraw
10. Threads and callbacks fun login(name, pass) { val thread = Thread(Runnable() -> { requestLogin(name, pass) { result -> show(result) //non-ui thread? } } thread.start() }
11. Threads and callbacks fun login(name, pass) { val thread = Thread(Runnable() -> { requestLogin(name, pass) { result -> Handler(Looper.getMainLooper()) { show(result) //back to Main } } } thread.start() }
12. onDraw onDraw onDraw requestLogin UI Thread show onDraw onDraw onDraw onDraw Coroutine Suspendable Computation
13. Coroutine • Write asynchronous code sequentially • ~lightweight thread fun login(name, pass) = launch { val result = requestLogin(name, pass) show(result) }
14. Coroutine • Not bound to specific Thread • Complete with a result fun login(name, pass) = launch(Dispatchers.IO){ val result = requestLogin(name, pass) withContext(Dispatchers.Main) { show(result) } }
15. Coroutine • Suspend function • Non-blocking Execution requestLogin Thread show Suspension point
16. suspend fun requestLogin( name: String, pass: String ): Result {...} Coroutine Suspend function
17. Coroutine Suspend function suspend fun requestLogin( name: String, pass: String ): Result = withContext(Dispatchers.IO) { ... } Suspending functions do not block the caller thread.
18. Dispatchers.Default • Common pool of shared background threads • Use it for: computing-intensive coroutines Dispatchers.Unconfined • Doesn’t confine the coroutine to any specific thread • Don’t use it in code 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
19. Coroutine Suspend function Suspension functions can only be called from other suspension functions or from coroutines suspend fun login(name, pass) { val result = requestLogin(name, pass) //suspend show(result) }
20. Sequencial & Data Dependencies suspend fun login(name, pass) { val authToken = authenticate() //suspend val result = requestLogin(authToken, name, pass) //suspend show(result) }
21. Errors suspend fun login(name, pass) { try { val result = requestLogin(name, pass) show(result) } catch (error: NetworkError){ //Handle error } }
22. Login button pressed Launch coroutine requestLogin Show login status val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job)
23. 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) }
24. 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) }
25. val job = Job() val uiScope = CoroutineScope(Dispatchers.Main + job) fun login( username: String, pass: String ) = uiScope.launch { val result = requestLogin(name, pass) show(result) } job.cancel()
26. Launching and cancelling coroutines Login button pressed Launch coroutine requestLogin Show login status Activity destroyed
27. Login button pressed Launch coroutine requestLogin Show login status ViewModel fun onCleared() { super.onCleared() job.cancel() }
28. 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() } }
29. lifecycle-viewmodel-ktx class MyViewModel: ViewModel() { fun login( username: String, pass: String ) = viewModelScope.launch(Dispatchers.IO) { val result = requestLogin(name, pass) show(result) } }
30. • Coroutines • suspend functions • Dispatchers • Launching a coroutine • Using a coroutine from ViewModels
31. codelabs.developers.google.com/ codelabs/kotlin-coroutines Useful Link
32. https://github.com/herisulistiyanto/devfest-coroutine Your turn