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SUSPENDERS
ANDROID
@chrisbanes
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ANDROID SUSPENDERS
chris.banes.me/suspenders
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Android’s main thread
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Android’s main thread
measure + layout
draw
View inflation
and many more things
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ms
60Hz
16
Android’s main thread
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12 ms
Android’s main thread
90Hz
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ms
120Hz
8
Android’s main thread
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No content
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ASYNC ALL THE THINGS
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How do we do that?
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Executors
AsyncTask
How do we do that?
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Loaders
Executors
AsyncTask
How do we do that?
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Future
Executors
Loaders
How do we do that?
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Libraries
Loaders
Future
How do we do that?
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WorkManager
Future
Libraries
How do we do that?
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Coroutines
Libraries
Coroutines
How do we do that?
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Coroutines
Libraries
Coroutines
So why use
?
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What does your typical
mobile app do?
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CRUD
What does your typical
mobile app do?
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C R U D
reate ead pdate elete
What does your typical
mobile app do?
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Sync
What does your typical
mobile app do?
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Sync
What does your typical
mobile app do?
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So why coroutines?
Scale on limited hardware
Easier development model
Great for I/O tasks
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Tivi
github.com/chrisbanes/tivi
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kotlinx-coroutines-core
-android
-rx2
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-core
-android
-rx2
jars: 774KB
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-core
-android
-rx2
jars: 774KB
apk: 499KB
3260 method refs
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-core
-android
-rx2
jars: 774KB
apk: 499KB
3260 method refs
r8: 113KB
1208 method refs
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-core
-android
-rx2
jars: 774KB
apk: 499KB
3260 method refs
r8: 113KB
1208 method refs
r8
optimized:
99KB
834 method refs
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-keepclassmembernames class kotlinx.** {
volatile ;
}
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ANDROID SUSPENDERS
Creating routines
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override suspend fun updateShow(showId: Long) {
val localResult = localShowStore.getShow(showId)
val result1 = remoteSource1.getShow(showId)
val result2 = remoteSource2.getShow(showId)
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
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override suspend fun updateShow(showId: Long) {
val localResult = localShowStore.getShow(showId)
val result1 = remoteSource1.getShow(showId)
val result2 = remoteSource2.getShow(showId)
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
1
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override suspend fun updateShow(showId: Long) {
val localResult = localShowStore.getShow(showId)
val result1 = remoteSource1.getShow(showId)
val result2 = remoteSource2.getShow(showId)
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
1
2
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override suspend fun updateShow(showId: Long) {
val localResult = localShowStore.getShow(showId)
val result1 = remoteSource1.getShow(showId)
val result2 = remoteSource2.getShow(showId)
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
1
2
3
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override suspend fun updateShow(showId: Long) {
val localResult = localShowStore.getShow(showId)
val result1 = remoteSource1.getShow(showId)
val result2 = remoteSource2.getShow(showId)
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
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override suspend fun updateShow(showId: Long) {
val localResult = localShowStore.getShow(showId)
val result1 = remoteSource1.getShow(showId)
val result2 = remoteSource2.getShow(showId)
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
1
2
3
Runs in 1.2 seconds
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override suspend fun updateShow(showId: Long) {
val localDeferred = async {
localShowStore.getShow(showId)
}
val remoteDeferred1 = async {
remoteSource1.getShow(showId)
}
val remoteDeferred2 = async {
remoteSource2.getShow(showId)
}
val localResult = localDeferred.await()
val result1 = remoteDeferred1.await()
val result2 = remoteDeferred2.await()
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
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override suspend fun updateShow(showId: Long) {
val localDeferred = async {
localShowStore.getShow(showId)
}
val remoteDeferred1 = async {
remoteSource1.getShow(showId)
}
val remoteDeferred2 = async {
remoteSource2.getShow(showId)
}
val localResult = localDeferred.await()
val result1 = remoteDeferred1.await()
val result2 = remoteDeferred2.await()
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
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override suspend fun updateShow(showId: Long) {
val localDeferred = async {
localShowStore.getShow(showId)
}
val remoteDeferred1 = async {
remoteSource1.getShow(showId)
}
val remoteDeferred2 = async {
remoteSource2.getShow(showId)
}
val localResult = localDeferred.await()
val result1 = remoteDeferred1.await()
val result2 = remoteDeferred2.await()
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
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override suspend fun updateShow(showId: Long) {
val localDeferred = async {
localShowStore.getShow(showId)
}
val remoteDeferred1 = async {
remoteSource1.getShow(showId)
}
val remoteDeferred2 = async {
remoteSource2.getShow(showId)
}
val localResult = localDeferred.await()
val result1 = remoteDeferred1.await()
val result2 = remoteDeferred2.await()
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
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override suspend fun updateShow(showId: Long) {
val localDeferred = async {
localShowStore.getShow(showId)
}
val remoteDeferred1 = async {
remoteSource1.getShow(showId)
}
val remoteDeferred2 = async {
remoteSource2.getShow(showId)
}
val localResult = localDeferred.await()
val result1 = remoteDeferred1.await()
val result2 = remoteDeferred2.await()
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
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override suspend fun updateShow(showId: Long) {
val localDeferred = async {
localShowStore.getShow(showId)
}
val remoteDeferred1 = async {
remoteSource1.getShow(showId)
}
val remoteDeferred2 = async {
remoteSource2.getShow(showId)
}
val localResult = localDeferred.await()
val result1 = remoteDeferred1.await()
val result2 = remoteDeferred2.await()
val merged = mergeShow(localResult, result1, result2)
localShowStore.saveShow(merged)
}.
Runs in 0.8 second
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How do we use them
on Android?
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class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
init {
refresh()
}
private fun refresh() {
launch {
showRepository.updateShow(showId)
// update view state
}
}
}
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class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
init {
refresh()
}
private fun refresh() {
launch {
showRepository.updateShow(showId)
// update view state
}
}
}
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class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
init {
refresh()
}
private fun refresh() {
launch {
showRepository.updateShow(showId)
// update view state
}
}
}
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class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
init {
refresh()
}
private fun refresh() {
launch {
showRepository.updateShow(showId)
// update view state
}
}
}
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class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
init {•
refresh()
}.
private fun refresh() {•
launch {•
showRepository.updateShow(showId)
// update view state
}.
}.
}.
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Jobs
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class ShowDetailsViewModel: ViewModel() {
private fun refresh() {
launch {
showRepository.updateShow(showId)
// update view state
}.
}.
}.
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class ShowDetailsViewModel: ViewModel() {
private fun refresh() {
val job = launch {
showRepository.updateShow(showId)
// update view state
}.
}.
}.
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class ShowDetailsViewModel: ViewModel() {
private fun refresh() {
val job = launch {
showRepository.updateShow(showId)
// update view state
}.
// can call job.cancel()
}.
}.
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class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private fun refresh() {
val job = launch {
showRepository.updateShow(showId)
// update view state
}.
// can call job.cancel()
}.
}.
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class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private fun refresh() {
updateShowJob = launch {
showRepository.updateShow(showId)
// update view state
}.
// can call job.cancel()
}.
}.
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class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private fun refresh() {
updateShowJob = launch {
showRepository.updateShow(showId)
// update view state
}.
}.
}.
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class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private fun refresh() {
updateShowJob = launch {
showRepository.updateShow(showId)
// update view state
}.
}.
override fun onCleared() {
updateShowJob ?.cancel()
}
}.
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class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private var updateEpisodesJob: Job? = null
private fun refresh() {
updateShowJob = launch {
showRepository.updateShow(showId)
// update view state
}.
updateShowJob = launch { ... }
}.
override fun onCleared() {
updateShowJob ?.cancel()
updateEpisodesJob ?.cancel()
}
}.
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class ShowDetailsViewModel: ViewModel() {
private var updateShowJob: Job? = null
private var updateEpisodesJob: Job? = null
private var updateCastJob: Job? = null
private fun refresh() {
updateShowJob = launch {
showRepository.updateShow(showId)
// update view state
}.
updateShowJob = launch { ... }
updateCastJob = launch { ... }
}.
override fun onCleared() {
updateShowJob ?.cancel()
updateEpisodesJob ?.cancel()
updateCastJob ?.cancel()
}
}.
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Coroutines can have a
parent-child relationship
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Coroutines can have a
parent-child relationship
Expressed via Jobs
(in a context)
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class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
private val job = Job()
init {•
refresh()
}.
private fun refresh() {•
launch(parent = job) {•
showRepository.updateShow(showId)
// update view state
}.
}.
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class ShowDetailsViewModel: ViewModel() {
val showRepository: ShowRepository = // ...
val state: LiveData
private val job = Job()
init {
refresh()
}.
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
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private val job = Job()
init {
refresh()
}.
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
job.cancel()
} ..
}.
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private val job = Job()
init {
refresh()
}.
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
job.cancel()
}
} ..
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private val job = Job()
init {
refresh()
}.
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
job.cancel()
}
} ..
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private val job = Job()
init {
refresh()
}.
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
job.cancel()
}
} ..
launch is now scoped to the
lifetime of the ViewModel
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Scopes
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private val job = Job()
init {
refresh()
}.
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
super.onCleared()
job.cancel()
}
} ..
Explicit
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launch(parent = job) {
}
suspend fun updateShow(showId: Long) {
val local = async {
localShowStore.getShow(showId)
}}
val remote = async {
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}.
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launch(parent = job) {
}
suspend fun updateShow(showId: Long) {
val local = async {
localShowStore.getShow(showId)
}}
val remote = async {
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}.
New coroutines
No parent
Suspended
job.cancel()
Cancelled
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init {
refresh()
}.
private fun refresh() {
launch(parent = job) {
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
Deprecated in v0.26
async too
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New!
v0.26
CoroutineScope
async & launch become instance methods
Allows objects to provide scope for coroutines
You provide a default context
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class ShowDetailsViewModel: ViewModel() {•
val showRepository: ShowRepository = // ...
val state: LiveData
private val job = Job()
init {
refresh()
}.
private fun refresh() {•
launch(parent = job) {•
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
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class ShowDetailsViewModel: ViewModel(), CoroutineScope {•
val showRepository: ShowRepository = // ...
val state: LiveData
private val job = Job()
init {
refresh()
}.
private fun refresh() {•
launch(parent = job) {•
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
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class ShowDetailsViewModel: ViewModel(), CoroutineScope {•
val showRepository: ShowRepository = // ...
val state: LiveData
private val job = Job()
override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
init {
refresh()
}.
private fun refresh() {•
launch(parent = job) {•
showRepository.updateShow(showId)
// update view state
}.
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override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
init {
refresh()
}.
private fun refresh() {•
launch(parent = job) {•
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {
super.onCleared()
job.cancel()
}.
}.
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override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
init {
refresh()
}.
private fun refresh() {•
launch {•
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {•
super.onCleared()
job.cancel()
}.
}.
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override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
init {
refresh()
}.
private fun refresh() {•
this.launch(context = coroutineContext) {•
showRepository.updateShow(showId)
// update view state
}.
}.
override onCleared() {•
super.onCleared()
job.cancel()
}.
}.
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open class ScopedViewModel : ViewModel(), CoroutineScope {
private val job = Job()
override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
override fun onCleared() {
super.onCleared()
job.cancel()
}
}
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launch {
}
suspend fun updateShow(showId: Long) {}
val local = async {}
localShowStore.getShow(showId)
}}
val remote = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}.
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launch {
}
suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
}}
val remote = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}.
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launch {
}
suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
}}
val remote = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}.
Child coroutines
Suspended
job.cancel()
Cancelled
Children are
cancelled too
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What if I’m not using
ViewModels?
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open class ScopedFragment : Fragment(), CoroutineScope {
private val job = Job()
override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main
override fun onDestroy() {
super.onDestroy()
job.cancel()
}
}
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// In your Activity / Fragment
val observer = MyObserver()
getLifecycle().addObserver(observer)
class MyObserver : DefaultLifecycleObserver {{
override fun onCreate(owner: LifecycleOwner) {{
// we’re created
}-
override fun onDestroy(owner: LifecycleOwner) {{
// we’re destroyed
})
}{
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class MyObserver : DefaultLifecycleObserver {{
override fun onCreate(owner: LifecycleOwner) {{
// we’re created
}-
override fun onDestroy(owner: LifecycleOwner) {{
// we’re destroyed
})
}{
// In your Activity / Fragment
val observer = MyObserver()
getLifecycle().addObserver(observer)
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class LifecycleScope : DefaultLifecycleObserver {{
override fun onDestroy(owner: LifecycleOwner) {{
// we’re destroyed
})
}{
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class LifecycleScope : DefaultLifecycleObserver {{
val job = Job(){
override fun onDestroy(owner: LifecycleOwner) {{
// we’re destroyed
})
}{
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class LifecycleScope : DefaultLifecycleObserver {{
val job = Job()
override fun onDestroy(owner: LifecycleOwner) {
// we’re destroyed{
job.cancel()
})
}{
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class LifecycleScope : DefaultLifecycleObserver, CoroutineScope {{
val job = Job()
override fun onDestroy(owner: LifecycleOwner) {
// we’re destroyed{
job.cancel()
})
}{
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class LifecycleScope : DefaultLifecycleObserver, CoroutineScope {{
val job = Job()
override val coroutineContext = job + Dispatchers.Main
override fun onDestroy(owner: LifecycleOwner) {
// we’re destroyed{
job.cancel()
})
}{
class DetailsFragment : Fragment() {
private val scope = LifecycleScope()
init {
lifecycle.addObserver(scope)
}}
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class DetailsFragment : Fragment() {
private val scope = LifecycleScope()
init {
lifecycle.addObserver(scope)
}}
override fun onCreateView( ...) {
// ...
}}
}}
// we’re destroyed{
job.cancel()
})
}{
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class DetailsFragment : Fragment() {
private val scope = LifecycleScope()
init {
lifecycle.addObserver(scope)
}}
override fun onCreateView( ...) {
// ...
}}
}}
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class DetailsFragment : Fragment() {
private val scope = LifecycleScope()
init {
lifecycle.addObserver(scope)
}}
override fun onStart() {
scope.launch {
// something async
}
}
override fun onCreateView( ...) {
// ...
}}
}}
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class DetailsFragment : Fragment() {
private val scope = LifecycleScope()
init {
lifecycle.addObserver(scope)
}}
override fun onStart() {
scope.launch {
// something async
}
}
override fun onCreateView( ...) {
// ...
}}
}}
Scoped to
Fragment lifecycle
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gist.louiscad.com/LifecycleCoroutines
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Cancellation
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Cancellation
requires co-operation
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Cancellation
requires co-operation
Need to check if cancelled
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Cancellation
requires co-operation
Need to check if active
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Call a suspending function
Check isActive
Two ways to co-operate
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Call a suspending function
Check isActive
if (job != null && !job.isActive) {
throw job.getCancellationException()
}
Two ways to co-operate
yield()
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Two ways to co-operate
Call a suspending function
Check isActive
launch {
files.forEach { file ->
if (isActive) doSomethingWith(file)
}
}
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Exceptions
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launch rethrows
exceptions
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suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
}}
val remote = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}}
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suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
}}
val trakt = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
// throws CrashyMcCrashfaceException()
}}
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suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
}}
val trakt = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
// throws CrashyMcCrashfaceException()
}}
Treated like an uncaught
exception
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async doesn’t throw
until await()
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suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
}}
val remote = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
}}
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suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
// throws CrashyMcCrashfaceException()
}}
val remote = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())}
localShowStore.saveShow(merged)}
}}
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suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
// throws CrashyMcCrashfaceException()
}}
val remote = async {}
remoteSource.getShow(showId)
}}
val merged = mergeShow(local.await(), remote.await())}
localShowStore.saveShow(merged)}
}}
Thrown here
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suspend fun updateShow(showId: Long) = coroutineScope {}
val local = async {}
localShowStore.getShow(showId)
// throws CrashyMcCrashfaceException()
}}
val remote = async {}
remoteSource.getShow(showId)
}}
try {}
val merged = mergeShow(local.await(), remote.await())
localShowStore.saveShow(merged)
} catch (t: Throwable) {}
// Handle the exception
}}
}}
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Dispatchers
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launch {{
// fun things
}}
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launch(context = Dispatchers.Default) {{
// fun things
}}
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What’s a
CoroutineDispatcher?
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What’s a
CoroutineDispatcher?
The thing which runs and
schedules coroutines
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DefaultScheduler
Dispatchers.Default
===
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DefaultScheduler
New!
v0.30
Elastic thread executor
Uses cpuCount threads (core)
Now set as Dispatchers.Default in 0.30
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New!
v0.25
IO
Designed for blocking I/O tasks
Uses 64 <= cpuCount threads
launch(IO) {{
// network things
}}
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IO
New!
v0.25
Shares threads
IO dispatcher uses DefaultScheduler
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New!
v0.25
async {
val local = withContext(IO) {
fileStore.loadImage( ...)
}}
// No thread context switch!
return processImage(local)
}}
Shares threads
IO dispatcher uses DefaultScheduler
IO
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async {
val local = withContext(IO) {
fileStore.loadImage( ...)
}}
// No thread context switch!
return processImage(local)
}}
Shares threads
IO dispatcher uses DefaultScheduler
New!
v0.25
IO
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async {
val local = withContext(IO) {
fileStore.loadImage(...)
}}
// No thread context switch!
return processImage(local)
}}
Shares threads
IO dispatcher uses DefaultScheduler
New!
v0.25
IO
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ANDROID SUSPENDERS
Reactivity
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Most devs use RxJava
for easy threading
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End up mainly using Single,
Maybe & Completable
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End up mainly using Single,
Maybe & Completable
Only exist in RxJava
RxScala
RxGroovy
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Coroutines
can replace
Single / Maybe / Completable
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service.trendingShows()
.scheduleOn(schedulers.io)
.subscribe(::onTrendingLoaded, ::onError)
interface RemoteService {}
@GET("/trendingshows")
fun trendingShows(): Single>
}}
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val show = withContext(dispatchers.io) {}
service.trendingShows().await()
}}
interface RemoteService {}
@GET("/trendingshows")
fun trendingShows(): Single>
}}
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val show = withContext(dispatchers.io) {}
service.trendingShows().await()
}}
interface RemoteService {}
@GET("/trendingshows")
fun trendingShows(): Single>
}}
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interface RemoteService {}
@GET("/trendingshows")
suspend fun trendingShows(): List
}}
val show = withContext(dispatchers.io) {}
service.trendingShows().await()
}}
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interface RemoteService {}
@GET("/trendingshows")
suspend fun trendingShows(): List
}}
val show = withContext(dispatchers.io) {}
service.trendingShows().await()
}}
Coming to Retrofit soon™
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interface RemoteService {}
@GET("/trendingshows")
suspend fun trendingShows(): List
}}
val show = withContext(dispatchers.io) {}
service.trendingShows().await()
}}
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interface RemoteService {}
@GET("/trendingshows")
suspend fun trendingShows(): List
}}
val show = withContext(dispatchers.io) {}
service.trendingShows()
}}
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Channels
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Be aware that Channels
is experimental
Channels
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Channels
Not a replacement for RxJava Publishers
Describe an asynchronous stream of things
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val channel = Channel()
launch {
// First coroutine to load images
files.forEach { file ->
val bitmap = loadBitmap(file)
channel.send(bitmap)
}
// We're done with the channel
channel.close()
}
launch {
// Second coroutine to process them
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val channel = Channel()
launch {
// First coroutine to load images
files.forEach { file ->
val bitmap = loadBitmap(file)
channel.send(bitmap)
}
// We're done with the channel
channel.close()
}
launch {
// Second coroutine to process them
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val channel = Channel()
launch {
// First coroutine to load images
files.forEach { file ->
val bitmap = loadBitmap(file)
channel.send(bitmap)
}
// We're done with the channel
channel.close()
}
launch {
// Second coroutine to process them
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val channel = Channel()
launch {
// First coroutine to load images
files.forEach { file ->
val bitmap = loadBitmap(file)
channel.send(bitmap)
}
// We're done with the channel
channel.close()
}
launch {
// Second coroutine to process them
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files.forEach { file ->
val bitmap = loadBitmap(file)
channel.send(bitmap)
}
// We're done with the channel
channel.close()
}
launch {
// Second coroutine to process them
channel.consumeEach { bitmap ->
processBitmap(bitmap)
}
}
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BroadcastChannels ≈ Subjects
ConflatedBroadcastChannel ≈ BehaviorSubject
Channels
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Channels support null values
Channels
Channels only support streams
"hot"
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Operators
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all any associate associateBy associateByTo
associateTo consume consumeEach consumeEachIndexed
consumes count distinct distinctBy drop dropWhile
elementAt elementAtOrElse elementAtOrNull filter
filterIndexed filterIndexedTo filterNot filterNotNull
filterNotNullTo filterNotTo filterTo find findLast
first firstOrNull flatMap fold foldIndexed groupBy
groupByTo indexOf indexOfFirst indexOfLast last
l a s t I n d e x O f l a s t O r N u l l m a p m a p I n d e x e d
mapIndexedNotNull mapIndexedNotNullTo mapIndexedTo
mapNotNull mapNotNullTo mapTo maxBy maxWith minBy
minWith none partition reduce reduceIndexed
requireNoNulls single singleOrNull sumBy sumByDouble
take takeWhile toChannel toCollection toList toMap
toMutableList toMutableSet toSet withIndex zip
Channels has 73
built-in operators
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aggregate
all
amb
ambWith
and
apply
asObservable
asyncAction
asyncFunc
averageDouble
length
limit
longCount
map
mapMany
materialize
max
maxBy
merge
mergeDelayError
Compare that to RxJava
230ish
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Operators are easier to write in
coroutines
fun Publisher.map(
context: CoroutineContext,
mapper: (T) -> R
) = GlobalScope.publish(context) {
consumeEach {
send(mapper(it))
}
}
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ANDROID SUSPENDERS
Using Android APIs
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Get last known location
One shot callback
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Get last known location
FusedLocationProviderClient
In Google Play Services
client.getLastLocation(): Task
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Get last known location
FusedLocationProviderClient
client.getLastLocation().addOnCompleteListener { task ->
// where am i?
val location = task.result
}
Location
In Google Play Services
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callback ➡ suspend
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callback ➡ suspend
suspendCoroutine { ... }
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suspendCoroutine { ... }
Given a continuation to later resume
Will run the lambda and then immediately suspend
How you pass the result back
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Get last known location
suspend fun getLastLocation(): Location {
}}
// TODO
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Get last known location
suspend fun getLastLocation(): Location {
return suspendCoroutine { continuation ->
}}
}}
// TODO
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Get last known location
suspend fun getLastLocation(): Location {
return suspendCoroutine { continuation ->
}}
}}
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Get last known location
suspend fun getLastLocation(): Location {
return suspendCoroutine { continuation ->
locationClient.lastLocation.addOnCompleteListener { task ->
continuation.resume(task.result)
}}
}}
}}
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Get last known location
suspend fun getLastLocation(): Location {
return suspendCoroutine { continuation ->
locationClient.lastLocation.addOnCompleteListener { task ->
continuation.resume(task.result)
}}
}}
}}
Resumes coroutine
with result
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Get last known location
suspend fun getLastLocation(): Location {
return suspendCoroutine { continuation ->
locationClient.lastLocation.addOnCompleteListener { task ->
if (task.isSuccessful) {
continuation.resume(task.result)
} else {
continuation.resumeWithException(task.exception !!)
}
}}
}}
}}
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Observe location updates
Multiple value callback
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FusedLocationProviderClient
Takes a callback parameter
fun requestLocationUpdates(
request: LocationRequest,
callback: LocationCallback,
looper: Looper
): Task
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fun requestLocationUpdates(
request: LocationRequest,
callback: LocationCallback,
looper: Looper
): Task
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fun requestLocationUpdates(
request: LocationRequest,
callback: LocationCallback,
looper: Looper
): Task
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fun requestLocationUpdates(
request: LocationRequest,
callback: LocationCallback,
looper: Looper
): Task
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fun requestLocationUpdates(
request: LocationRequest,
callback: LocationCallback,
looper: Looper
): Task
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fun removeLocationUpdates(
callback: LocationCallback
): Task
Remove the callback
when done
request: LocationRequest,
callback: LocationCallback,
looper: Looper
): Task
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel
Lets build our function...
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {}
}}
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {}
val channel = Channel()
// TODO update channel
return channel
}}
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {}
val channel = Channel()
val callback = object : LocationCallback() {
override fun onLocationResult(result: LocationResult) {
channel.sendBlocking(result.getLastLocation())
}}
}}
// TODO request location updates
return channel
}}
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
val callback = object : LocationCallback() {
override fun onLocationResult(result: LocationResult) {
channel.sendBlocking(result.getLastLocation())
}
}
// TODO request location updates
return channel
}
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
val callback = object : LocationCallback() {
override fun onLocationResult(result: LocationResult) {
channel.sendBlocking(result.getLastLocation())
}}
}}
// TODO request location updates
return channel
}}
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
val callback = object : LocationCallback() {
override fun onLocationResult(result: LocationResult) {
channel.sendBlocking(result.getLastLocation())
}}
}}
return channel
}}
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fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
val callback = object : LocationCallback() {
override fun onLocationResult(result: LocationResult) {
channel.sendBlocking(result.getLastLocation())
}}
}}
// Start location updates, sending locations to the
// channel
locationClient.requestLocationUpdates(
locationRequest,
callback,
Looper.myLooper()
)}
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val channel = Channel()
val callback = object : LocationCallback() {
override fun onLocationResult(result: LocationResult) {
channel.sendBlocking(result.getLastLocation())
}}
}}
// Start location updates, sending locations to the
// channel
locationClient.requestLocationUpdates(
locationRequest,
callback,
Looper.myLooper()
)}
return channel
}}
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}}
// Start location updates, sending locations to the
// channel
locationClient.requestLocationUpdates(
locationRequest,
callback,
Looper.myLooper()
)}
// Remove the location callback when the channel
// is closed
channel.invokeOnClose {
locationClient.removeLocationUpdates(callback)
}
return channel
}}
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lateinit var locationChannel: ReceiveChannel
override fun onStart() {
val locationRequest = LocationRequest()
.setSmallestDisplacement(100f) // 100m
locationChannel = observeLocation(locationRequest)
launch(Main) {
locationChannel.consumeEach {
// We have a new location!
updateUiForLocation(it)
}
}
}
override fun onStop() {
// Stop observing the location and
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lateinit var locationChannel: ReceiveChannel
override fun onStart() {
val locationRequest = LocationRequest()
.setSmallestDisplacement(100f) // 100m
locationChannel = observeLocation(locationRequest)
launch(Main) {
locationChannel.consumeEach {
// We have a new location!
updateUiForLocation(it)
}
}
}
override fun onStop() {
// Stop observing the location and
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lateinit var locationChannel: ReceiveChannel
override fun onStart() {
val locationRequest = LocationRequest()
.setSmallestDisplacement(100f) // 100m
locationChannel = observeLocation(locationRequest)
launch(Main) {
locationChannel.consumeEach {
// We have a new location!
updateUiForLocation(it)
}
}
}
override fun onStop() {
// Stop observing the location and
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lateinit var locationChannel: ReceiveChannel
override fun onStart() {
val locationRequest = LocationRequest()
.setSmallestDisplacement(100f) // 100m
locationChannel = observeLocation(locationRequest)
launch(Main) {
locationChannel.consumeEach {
// We have a new location!
updateUiForLocation(it)
}}
}}
}}
override fun onStop() {
// Stop observing the location and
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.setSmallestDisplacement(100f) // 100m
locationChannel = observeLocation(locationRequest)
launch(Main) {
locationChannel.consumeEach {
// We have a new location!
updateUiForLocation(it)
}}
}}
}}
override fun onStop() {
// Stop observing the location and
// close the channel
locationChannel.cancel()
}}
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.setSmallestDisplacement(100f) // 100m
locationChannel = observeLocation(locationRequest)
launch(Main) {
locationChannel.consumeEach {
// We have a new location!
updateUiForLocation(it)
}}
}}
}}
override fun onStop() {
// Stop observing the location and
// close the channel
locationChannel.cancel()
}}
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ANDROID SUSPENDERS
What's next?
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Codelab
https:/
/codelabs.developers.google.com/codelabs/kotlin-coroutines/
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RTFM
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Exploring Coroutines in
Kotlin
Kotlin Coroutines in
Practice
Coroutines and Reactive
Programming - friends or foes?
Effectenbeurzaal
Tomorrow, 13:00
Effectenbeurzaal
Tomorrow, 10:15
Granbeurszaal
Tomorrow, 15:15
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Over and out…
@chrisbanes