Exploring Kotlin

Exploring Kotlin
Atiq Ur Rehman
@TheMaxCoder

Atiq Ur Rehman - Freelance Android Developer

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

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

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

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

Kotlin/Android
- Officially Supported
- Android KTX

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

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

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

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
}

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

for (element in this) action(element)
}

for (element in this){
action(element)
}
}
// Usage
list.forEach { print(it) }

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

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

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

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

Named Arguments
requestLogin(pass = “Kotlin”)

Using Kotlin Coroutines
in your Android App

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

Challenge 1: Execute on a non-UI thread

Challenge 2: Get informed when the task is done

Challenge 2: Get informed when the task is done
Android solutions
● AsyncTask
● Loaders (deprecated in Android P)
● RxJava
● Thread / HandlerThread / Executor with callbacks

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

val thread = Thread(Runnable() -> {
requestLogin(name, pass) { result ->
Handler(Looper.getMainLooper()) {
show(result)
}
}

requestLogin(name, pass) { result -> show(result) }
}

UI Thread
}

Coroutine
= suspendable computation
UI Thread

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

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

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

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

}
Thread

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

): Result {...}
Suspending functions do not block the caller thread.

): Result = withContext(Dispatchers.IO) {
...
}

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

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

Dispatchers.Default
Dispatchers.IO
● Shared pool of on-demand created threads
● Use it for: IO-intensive blocking operations
Dispatchers.Main
● Main thread

Dispatchers.Default
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

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

val authToken = authenticate()
val result = requestLogin(authToken, name, pass)
show(result)
}
Sequential

val authToken = authenticate()
val result = requestLogin(authToken, name, pass)
show(result)
}
Data dependencies

try {
show(result)
} catch (error: NetworkError){
}
}
Errors

Launching and cancelling coroutines

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

val job = Job()
fun login(username: String, pass: String
) = uiScope.launch {
show(result)
}

val job = Job()
fun login(username: String, pass: String
) = uiScope.launch(Dispatchers.IO) {
show(result)
}

val job = Job()
fun login(
username: String, pass: String
) = uiScope.launch {
show(result)
}
job.cancel()

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

class MyViewModel: ViewModel() {
val viewModelJob = Job()
val uiScope = CoroutineScope(Dispatchers.Main+viewModelJob)
fun login(
show(result)
}
fun onCleared() {
super.onCleared()
viewModelJob.cancel()
}
}

val viewModelJob = Job()
val uiScope = CoroutineScope(Dispatchers.Main+viewModelJob)
fun login(
show(result)
}
fun onCleared() {
super.onCleared()
viewModelJob.cancel()
}
}
lifecycle-viewmodel-ktx

fun login(
) = viewModelScope.launch(Dispatchers.IO) {
show(result)
}
}

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

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

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

Exploring Kotlin

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Editor's Notes