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5 RXJAVA TIPS
YOU MIGHT NOT KNOW
HIROSHI KUROKAWA (FABLIC, INC.)
POTATOTIPS #29, MAY 25TH, 2016
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription signInSubscription = null;
private void sendSignInRequest() {
signInSubscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
if (signInSubscription != null) {
signInSubscription.unsubscribe();
}
super.onDestroy();
}
▸ In RxJava, it’s really important to call unsubscribe()
▸ If you forgot it, memory leak would occur
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription signInSubscription = null;
private void sendSignInRequest() {
signInSubscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
if (signInSubscription != null) {
signInSubscription.unsubscribe();
}
super.onDestroy();
}
▸ In RxJava, it’s really important to call unsubscribe()
▸ If you forgot it, memory leak would occur
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription subscription = null;
private void sendSignInRequest() {
subscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
if (subscription != null) {
subscription.unsubscribe();
}
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription subscription = null;
private void sendSignInRequest() {
subscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
if (subscription != null) {
subscription.unsubscribe();
}
super.onDestroy();
}
Use Subscriptions.empty() instead
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription subscription = null;
private void sendSignInRequest() {
subscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
if (subscription != null) {
subscription.unsubscribe();
}
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription subscription =
private void sendSignInRequest() {
subscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
if (subscription != null) {
subscription.unsubscribe();
}
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription subscription = Subscriptions.empty();
private void sendSignInRequest() {
subscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
if (subscription != null) {
subscription.unsubscribe();
}
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
1. AVOID NULL CHECK FOR SUBSCRIPTION - SINGLE
private Subscription subscription = Subscriptions.empty();
private void sendSignInRequest() {
subscription = service.signInUser(new SignInRequest(email, password))
.subscribe(...);
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
2. REPLACE AN EXISTING SUBSCRIPTION
private Subscription subscription = Susbscriptions.empty();
// can be called multiple times
private void update() {
// cancel the previous request if necessary
if (!subscription.isUnsubscribed()) {
subscription.unsubscribe();
}
subscription = service.fetchData()
.subscribe(...);
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
Awkward
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POTATOTIPS #29 (2016-05-25)
2. REPLACE AN EXISTING SUBSCRIPTION
private Subscription subscription = Susbscriptions.empty();
// can be called multiple times
private void update() {
// cancel the previous request if necessary
if (!subscription.isUnsubscribed()) {
subscription.unsubscribe();
}
subscription = service.fetchData()
.subscribe(...);
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
2. REPLACE AN EXISTING SUBSCRIPTION
private Subscription subscription =
// can be called multiple times
private void update() {
// cancel the previous request if necessary
if (!subscription.isUnsubscribed()) {
subscription.unsubscribe();
}
subscription = service.fetchData()
.subscribe(...);
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
2. REPLACE AN EXISTING SUBSCRIPTION
private SerialSubscription subscription = new SerialSubscription();
// can be called multiple times
private void update() {
// cancel the previous request if necessary
if (!subscription.isUnsubscribed()) {
subscription.unsubscribe();
}.
subscription = service.fetchData()
.subscribe(...);
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
2. REPLACE AN EXISTING SUBSCRIPTION
private SerialSubscription subscription = new SerialSubscription();
// can be called multiple times
private void update() {
// cancel the previous request if necessary
subscription = service.fetchData()
.subscribe(...);
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
2. REPLACE AN EXISTING SUBSCRIPTION
private SerialSubscription subscription = new SerialSubscription();
// can be called multiple times
private void update() {
// cancel the previous request if necessary
subscription.set(service.fetchData()
.subscribe(...));
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
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POTATOTIPS #29 (2016-05-25)
2. REPLACE AN EXISTING SUBSCRIPTION
private SerialSubscription subscription = new SerialSubscription();
// can be called multiple times
private void update() {
// cancel the previous request if necessary
subscription.set(service.fetchData()
.subscribe(...));
}
@Override
public void onDestroy() {
subscription.unsubscribe();
super.onDestroy();
}
The previous subscription is automatically
unsubscribed
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POTATOTIPS #29 (2016-05-25)
3. APPLY A COMMON SET OF OPERATORS WITH COMPOSE()
private void update() {
// cancel the previous request if necessary
subscription = service.fetchData()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}
Applying the same thread operators
every time? Use compose()
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POTATOTIPS #29 (2016-05-25)
3. APPLY A COMMON SET OF OPERATORS WITH COMPOSE()
private void update() {
// cancel the previous request if necessary
subscription = service.fetchData()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
}
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POTATOTIPS #29 (2016-05-25)
3. APPLY A COMMON SET OF OPERATORS WITH COMPOSE()
private void update() {
// cancel the previous request if necessary
subscription = service.fetchData()
.subscribe(...);
}
public static Observable.Transformer applySchedulers() {
return new Observable.Transformer() {
@Override
public Observable call(Observable observable) {
return observable
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
};
}
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POTATOTIPS #29 (2016-05-25)
3. APPLY A COMMON SET OF OPERATORS WITH COMPOSE()
private void update() {
// cancel the previous request if necessary
subscription = service.fetchData()
.compose(RxUtil.applySchedulers())
.subscribe(...);
}
public static Observable.Transformer applySchedulers() {
return new Observable.Transformer() {
@Override
public Observable call(Observable observable) {
return observable
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread());
}
};
}
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POTATOTIPS #29 (2016-05-25)
4. AVOID A CUSTOM ONSUBSCRIBE
public static Observable do() {
return Observable.create(subscriber -> {
try {
subscriber.onNext(doSomething());
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
});
}
▸ Don’t create your OnSubscribe if possible
▸ It’s hard to implement properly
Observable contract, Backpressure, Subscription handling
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POTATOTIPS #29 (2016-05-25)
4. AVOID A CUSTOM ONSUBSCRIBE
public static Observable do() {
return Observable.create(subscriber -> {
try {
subscriber.onNext(doSomething());
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
});
}
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POTATOTIPS #29 (2016-05-25)
4. AVOID A CUSTOM ONSUBSCRIBE
public static Observable do() {
return Observable. (subscriber -> {
try {
subscriber.onNext(doSomething());
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
});
}
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POTATOTIPS #29 (2016-05-25)
4. AVOID A CUSTOM ONSUBSCRIBE
public static Observable do() {
return Observable.fromCallable(subscriber -> {
try {
subscriber.onNext(doSomething());
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
});
}
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POTATOTIPS #29 (2016-05-25)
4. AVOID A CUSTOM ONSUBSCRIBE
public static Observable do() {
return Observable.fromCallable(() -> {
try {
subscriber.onNext(doSomething());
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
});
}
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POTATOTIPS #29 (2016-05-25)
4. AVOID A CUSTOM ONSUBSCRIBE
public static Observable do() {
return Observable.fromCallable(() -> doSomething());
}
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POTATOTIPS #29 (2016-05-25)
4. AVOID A CUSTOM ONSUBSCRIBE
public static Observable do() {
return Observable.fromCallable(() -> doSomething());
}
▸ Don’t create your OnSubscribe if possible
▸ Use Observable.fromCallable() instead
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POTATOTIPS #29 (2016-05-25)
5. CONCAT().FIRST() FOR MULTIPLE RESOURCE ACCESS
▸ concat(observable1, observable2, …)
▸ Concatenates the events emit from the observables
▸ Take events from ovservable1
▸ On completed, take events from observable2
▸ And so on
▸ first(condition)
▸ Filters the events and returns the first event satisfying the condition
▸ concat().first()
▸ Access the observables one by one and returns the first valid resource
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POTATOTIPS #29 (2016-05-25)
5. CONCAT().FIRST() FOR MULTIPLE RESOURCE ACCESS
// Create our sequence for querying best available data
Observable source = Observable.concat(
sources.memory(),
sources.disk(),
sources.network()
)
.first(data -> data != null && data.isUpToDate());
from https://github.com/dlew/rxjava-multiple-sources-sample
▸ Check memory/disk/network one by one and return the
available data