As presented at the 2019 Google Developer Group Cloud's KotlinEverywhere event in Islamabad, Pakistan.

1. Exploring Kotlin
Atiq Ur Rehman
@TheMaxCoder

2. Atiq Ur Rehman - Freelance Android Developer

3. Introduction to Kotlin

4. What is Kotlin
- General-purpose
- OOP + FP
- Static typing
- Open source (Apache 2.0)
- Developed by JetBrains

5. Kotlin Philosophy
- Concise
- Safe
- Interoperable
- Tool-friendly

6. Timeline
2010 Project started
2016 Kotlin 1.0
2017 Official on Android
2018 Kotlin 1.3

7. Current adoption

8. Build Applications For

9. Kotlin/JVM
- Supports JVM 1.6+
- 100% Java Interop
- You can use all the existing Java frameworks & libraries
- Automatic Java to Kotlin conversion

10. Kotlin/Android
- Officially Supported
- Android KTX

11. Kotlin/JS
- Transpile to JavaScript
- Readable generated JS code
- JS interop

12. Kotlin/Native
- Targets
- iOS / Android
- Windows, Linux, Mac
- Small Devices
- C, Swift, Objective-C

13. Multiplatform projects

14. Some Kotlin Features

15. Extension functions
fun Date.isSaturday(): Boolean {
return day == 6
}

16. val today = Date(2019, 6, 22)
if(today.isSaturday()) {
println("Today is a Saturday")
} else {
println("Today is not a Saturday")
}
fun Date.isSaturday(): Boolean {
return day == 6
}

17. Higher-Order Functions
fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
for (element in this){
action(element)
}
}

18. Higher-Order Functions
fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
for (element in this) action(element)
}

19. Higher-Order Functions
fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
for (element in this) action(element)
}

20. Higher-Order Functions
fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
for (element in this){
action(element)
}
}

21. Higher-Order Functions
fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit {
for (element in this){
action(element)
}
}
// Usage
list.forEach { print(it) }

22. Named Arguments
fun requestLogin(name: String, pass: String)

23. Named Arguments
requestLogin(name = “Atiq”, pass = “kotlin”)

24. Named Arguments
requestLogin(pass = “kotlin”, name = “Atiq”)

25. Named Arguments
fun requestLogin(name: String = “Atiq”, pass: String)

26. Named Arguments
requestLogin(pass = “Kotlin”)

27. Using Kotlin Coroutines
in your Android App

28. Long running tasks
● Network requests
● Database operations
● Image processing
● ...

29. Challenge 1: Execute on a non-UI thread

30. Challenge 1: Execute on a non-UI thread
Challenge 2: Get informed when the task is done

31. Challenge 1: Execute on a non-UI thread
Challenge 2: Get informed when the task is done
Android solutions
● AsyncTask
● Loaders (deprecated in Android P)
● RxJava
● Thread / HandlerThread / Executor with callbacks

32. Threads and callbacks
fun login(name, pass) {
val thread = Thread(Runnable() -> {
requestLogin(name, pass) { result ->
show(result)
}
}
thread.start()
}

33. Threads and callbacks
fun login(name, pass) {
val thread = Thread(Runnable() -> {
requestLogin(name, pass) { result ->
Handler(Looper.getMainLooper()) {
show(result)
}
}

34. Threads and callbacks
fun login(name, pass) {
requestLogin(name, pass) { result -> show(result) }
}

35. UI Thread
fun login(name, pass) {
requestLogin(name, pass) { result -> show(result) }
}

36. UI Thread
fun login(name, pass) {
requestLogin(name, pass) { result -> show(result) }
}

37. UI Thread
fun login(name, pass) {
requestLogin(name, pass) { result -> show(result) }
}

38. Coroutine
= suspendable computation
UI Thread

39. https://medium.com/@elye.project/understanding-suspend-function-of-coroutines-de26b070c5ed

40. https://medium.com/@elye.project/understanding-suspend-function-of-coroutines-de26b070c5ed

41. Coroutine
Write asynchronous code sequentially
fun login(name, pass) = launch {
val result = requestLogin(name, pass)
show(result)
}

42. Coroutine
~ lightweight thread
fun login(name, pass) = launch {
val result = requestLogin(name, pass)
show(result)
}

43. fun login(name, pass) = launch(Dispatchers.IO){
val result = requestLogin(name, pass)
withContext(Dispatchers.Main) {
show(result)
}
}
Coroutine
● Not bound to a specific thread
● Complete with a result

44. fun login(name, pass) {
requestLogin(name, pass) { result -> show(result) }
}
Thread

45. suspend fun requestLogin(
name: String, pass: String
): Result {...}

46. suspend fun requestLogin(
name: String, pass: String
): Result {...}
Suspending functions do not block the caller thread.

47. suspend fun requestLogin(
name: String, pass: String
): Result = withContext(Dispatchers.IO) {
...
}

48. Dispatchers.Main
● Main thread
● Use it for: UI operations

49. Dispatchers.Default
● Common pool of shared background threads
● Use it for: computing-intensive coroutines
Dispatchers.Main
● Main thread
● Use it for: UI operations

50. 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

51. 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

52. suspend fun requestLogin(
name: String, pass: String
): Result = withContext(Dispatchers.IO) {
...
}

53. suspend fun login(name, pass) {
val result = requestLogin(name, pass)
show(result)
}
suspend fun requestLogin(
name: String, pass: String
): Result = withContext(Dispatchers.IO) {
...
}

54. suspend fun login(name, pass) {
val authToken = authenticate()
val result = requestLogin(authToken, name, pass)
show(result)
}
Sequential

55. suspend fun login(name, pass) {
val authToken = authenticate()
val result = requestLogin(authToken, name, pass)
show(result)
}
Data dependencies

56. suspend fun login(name, pass) {
try {
val result = requestLogin(name, pass)
show(result)
} catch (error: NetworkError){
}
}
Errors

57. Launching and cancelling coroutines

58. val job = Job()
val uiScope = CoroutineScope(Dispatchers.Main + job)

59. val job = Job()
val uiScope = CoroutineScope(Dispatchers.Main + job)
fun login(username: String, pass: String
) = uiScope.launch {
val result = requestLogin(name, pass)
show(result)
}

60. 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)
}

61. 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()

62. Launching and cancelling coroutines

63. Launching and cancelling coroutines

64. fun onCleared() {
super.onCleared()
job.cancel()
}

65. 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()
}
}

66. 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

67. class MyViewModel: ViewModel() {
fun login(
username: String, pass: String
) = viewModelScope.launch(Dispatchers.IO) {
val result = requestLogin(name, pass)
show(result)
}
}

68. ● Coroutines
● suspend functions
● Dispatchers
● Launching a coroutine
● Using a coroutine from ViewModels

69. Useful Links
kotlinlang.org
try.kotlinlang.org and Kotlin Koans
Slack: slack.kotl.in

70. Thank You!
Slack Community of 150+ Pakistani Android Developers from all over the world
http://bit.ly/androiddevs-pakistan
TheMaxCoderr
facebook.com/TheMaxCoder