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RxJava
A Stream of Joy and Woe
@chris_h_codes
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Why have we chased
the dragon?
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webServices.getSomething()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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webServices.getSomething()
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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webServices.getSomething()
.flatMap { firstResult -> webServices.getSomethingElse(firstResult) }
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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webServices.getSomething()
.flatMap { firstResult -> webServices.getSomethingElse(firstResult) }
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe (
{ something ->
// ...
},
{ error ->
// ...
}
)
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webServices.getSomething()
.flatMap { firstResult -> webServices.getSomethingElse(firstResult) }
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe (
{ something ->
// ...
},
{ error ->
// ...
}
)
OF
TERMINAL EVENTS
BEWARE
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val getSomethingFromWeb = webServices.getSomething()
.flatMap { firstResult -> webServices.getSomethingElse(firstResult) }
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
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systemEventEmitter()
.switchMap { getSomethingFromWeb.toObservable() }
.withLatestFrom(somethingElse) {
// ...
}
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interface WebServices {
@GET("something")
fun getSomething(): Single>
}/
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interface WebServices {
@GET("something")
fun getSomething(): Single>
}/
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webServices.getSomething()
.flatMap { firstResult -> webServices.getSomethingElse(firstResult) }
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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webServices.getSomething()
.flatMap { firstResult -> webServices.getSomethingElse(firstResult) }
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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webServices.getSomething()
.flatMap { firstResult ->
if (!firstResult.isError()) {
webServices.getSomethingElse(firstResult.response().body())
} else {
Single.just(ERROR)
}/
}/
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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webServices.getSomething()
.flatMap { firstResult ->
if (!firstResult.isError() && firstResult.response().isSuccessful) {
webServices.getSomethingElse(firstResult.response().body())
} else {
Single.just(ERROR)
}/
}/
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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webServices.getSomething()
.flatMap { firstResult ->
if (!firstResult.isError() && firstResult.response().isSuccessful) {
webServices.getSomethingElse(firstResult.response().body())
} else {
Single.just(ERROR)
}/
}/
.map { result -> transform(result) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { something ->
// ...
}/
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suspend fun doSomeWork() {
try {
val firstResponse = webServices.getSomething().await()
if (firstResponse.isSuccessful) {
val something = firstResponse.body()
val secondResponse = webServices.getSomethingElse(something).await()
// ..
}
} catch (e: IOException) {
// ..
}
}
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• Interfacing with an engine monitoring system
• Over bluetooth
• Which is emulating a serial connection
• Enabling a (very slow) satellite internet service
• Via SOAP
• Sending location and engine data over that
connection
• Meanwhile monitoring the accelerometer to check
for accidents
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Monitoring for accidents
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Z
X
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Y
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android.hardware.Sensor.TYPE_GRAVITY
XYZ XYZ XYZ
XZ XZ XZ
XYZ
Check against some threshold
!
Throttle detections
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sensors.observeSensor(TYPE_GRAVITY)
.distinctUntilChanged()
.map { it.sensorEvent.values }
.filter { it[0] > ROLLOVER_THRESHOLD || it[2] > ROLLOVER_THRESHOLD }
.map { Emergency.ROLLOVER }
.throttleFirst(THROTTLE_SECONDS, TimeUnit.SECONDS)
.observeOn(RealRxSchedulers.mainThread())
.subscribe { }
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• Location updates
• Bluetooth payloads from engine
• Managing output sockets as network conditions change
• Shift status timers
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RxPermissions
.request(Manifest.permission.CAMERA)
.subscribe { granted ->
if (granted) {
// I can control the camera now.
} else {
// Oh no, permission denied.
}
}
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RxActivityResult.on(this)
.startIntent(takePhoto)
.subscribe { result, resultCode ->
if (resultCode == RESULT_OK) {
result.targetUi().showImage(data)
} else {
result.targetUi().printUserCancelled()
}
}
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13:37
chris_h_codes
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13:37
chris_h_codes
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13:37
chris_h_codes
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fun onViewAttached() {
val user = userStore.getCurrentValue()
avatarView.setImage(user.profilePic)
usernameView.text = user.username
}/
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fun onViewAttached() {
val user = userStore.getCurrentValue()()
avatarView.setImage(user.profilePic)
usernameView.text = user.username
userStore.observe().subscribe { user ->
avatarView.setImage(user.profilePic)
usernameView.text = user.usernmame
}
}/
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https:/
/github.com/Gridstone/RxStore
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https:/
/github.com/Gridstone/RxStore
val userStore = storeProvider.valueStore(file, converter)
userStore.put(user)
val observeUser: Observable = userStore.observe()
val putUser: Single = userStore.observePut(user)
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webServices.getUser()
.concatMap { user -> userStore.observePut(user) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
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Controller
View
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Controller
View
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State
Controller
View
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Controller
View
State
Event
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Controller
View
Observable
Observable
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val events: Observable = Observable.merge(
loginButton.clicks().map { Event.AttemptLogin(username, password) },
cancelButton.clicks().map { Event.Cancel }
)
https:/
/github.com/JakeWharton/RxBinding
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Observables
.combineLatest(
usernameView.textChanges().map { it.isNotEmpty() },
passwordView.textChanges().map { it.isNotEmpty() })
{ hasUsername, hasPassword -> hasUsername && hasPassword }
.subscribe(loginButton::setEnabled)
Username
Password
Login
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Controller
View
Observable
Observable
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View()
onFinishInflate()
onRestoreInstanceState()
draw()
display(state)
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stateStream
.subscribeOn(Schedulers.computation())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { state ->
view.display(state)
}/
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stateStream
.replay(1)
.autoConnect()
.subscribeOn(Schedulers.computation())
.observeOn(AndroidSchedulers.mainThread())
.subscribe { state ->
view.display(state)
}/
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stateStream
.subscribeOn(Schedulers.computation())
.observeOn(AndroidSchedulers.mainThread())
.replay(1)
.autoConnect()
.subscribe { state ->
view.display(state)
}/
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stateStream
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action
state
reduce(action, previousState)
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Takeaways
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Takeaways
• If you only use Rx for callbacks with nice threading, consider coroutines
• Beware terminal events
• Be mindful of thread boundaries and state delivery
• Don’t try to Rx-AllTheThings
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RxJava
A Stream of Joy and Woe
chris_h_codes
chris-horner
chrishorner.codes