This document discusses using Kotlin coroutines in Android applications. It explains that coroutines allow suspending functions without blocking threads, providing an easier way to do asynchronous programming. It shows how to launch coroutines using launch and async/await. It also demonstrates how suspending functions can be used to suspend coroutines instead of using callbacks to chain asynchronous operations like network requests sequentially.

1. KOTLIN
COROUTINES
in Android

2. 2018 / KOTLIN COROUTINES IN ANDROID
COROUTINES
Async
easy
Coroutines provide a way to
avoid blocking a thread and
simplify asynchronous
programming
SLIDE HEADLINE / Kotlin Coroutines in Android

3. COROUTINES
SLIDE HEADLINE / Kotlin Coroutines in Android
Blocking vs
Suspending
Coroutines are computations
that can be suspended without
blocking a thread
Suspending
2018 / KOTLIN COROUTINES IN ANDROID

4. COROUTINES
SLIDE HEADLINE / Kotlin Coroutines in Android
Launch
launch { … } is a Kotlin regular
function, which takes
suspending block and returns a
Job instance
Suspending
Launch
2018 / KOTLIN COROUTINES IN ANDROID

5. COROUTINES
SLIDE HEADLINE / Kotlin Coroutines in Android
Async
Await
async { … } in Kotlin is regular
function with suspending
parameter
await() is a method to get value
from suspending function done
asynchronous
Suspending
Launch
Async / await
2018 / KOTLIN COROUTINES IN ANDROID

6. Network
request
We want to send a request to
get some information …
fun getLocation(): Location {
/// gets current location
return location
}
2018 / KOTLIN COROUTINES IN ANDROID

7. Network
request
… and some more information
based on previous ...
fun getLocation(): Location { … }
fun getWeather(location: Location): Weather {
/// gets weather for current location
return weather
}
2018 / KOTLIN COROUTINES IN ANDROID

8. Network
request
… and show the result
fun getLocation(): Location { … }
fun getWeather(location: Location): Weather { … }
fun showWeather(weather: Weather) {
/// shows weather on the screen
}
2018 / KOTLIN COROUTINES IN ANDROID

9. fun getLocationAsync(cb: (Location) -> Unit) {
/// gets current location and returns it
/// with callback when done
}
Callbacks
We can do same with callbacks
2018 / KOTLIN COROUTINES IN ANDROID

10. fun getLocationAsync(cb: (Location) -> Unit) { … }
fun getWeatherAsync(location: Location,
cb: (Weather) -> Unit) {
/// gets weather for current location async
}
Callbacks
We can do same with callbacks
2018 / KOTLIN COROUTINES IN ANDROID

11. fun getLocationAsync(cb: (Location) -> Unit) { … }
fun getWeatherAsync(location: Location,
cb: (Weather) -> Unit) { … }
fun showWeather(weather: Weather) {
/// shows weather on the screen
}
Callbacks
We can do same with callbacks
2018 / KOTLIN COROUTINES IN ANDROID

12. fun getLocationAsync(cb: (Location) -> Unit) { … }
fun getWeatherAsync(location: Location,
cb: (Weather) -> Unit) { … }
fun showWeather(weather: Weather) { … }
fun processWeather() {
getLocationAsync { location ->
getWeatherAsync { weather ->
showWeather(weather)
}
}
}
Callbacks
We can do same with callbacks
2018 / KOTLIN COROUTINES IN ANDROID

13. Suspending
function
Suspending function suspends
the coroutine, without blocking
the thread
suspend fun getLocation(): Location {
/// gets current location & suspends
return location
}
2018 / KOTLIN COROUTINES IN ANDROID

14. Suspending
function
Suspending function suspends
the coroutine, without blocking
the thread
suspend fun getLocation(): Location { … }
suspend fun getWeather(location: Location): Weather {
/// gets weather for current location &
/// suspends
return weather
}
2018 / KOTLIN COROUTINES IN ANDROID

15. Suspending
function
Suspending function suspends
the coroutine, without blocking
the thread
2018 / KOTLIN COROUTINES IN ANDROID
suspend fun getLocation(): Location { … }
suspend fun getWeather(location: Location)
: Weather { … }
fun showWeather(weather: Weather) {
/// shows weather on the screen
}
suspend fun processWeather() {
val location = getLocation()
val weather = getWeather(location)
showWeather(weather)
}

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17. Launch
coroutine
/** Simple countdown with coroutines */
fun countdown(start: Int) {
launch(UI) {
for (i in start downTo 0) {
/// show time
delay(1000)
}
}
}
2018 / KOTLIN COROUTINES IN ANDROID

18. Place your screenshot
here
2018 / KOTLIN COROUTINES IN ANDROID

19. Thanks!
Any questions?
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me@robertlevonyan.com
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