Create an Observable that generates a Single on subscribe, but which stops and reuses a specific value
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I'm using Retrofit to make an API call, which returns a Single, and I use onErrorReturn to convert any exceptions to a default object. I want consumers to see the current value, but if the current value is the default object, I want to try to requery the API and send that result out in addition. To complicate things, I might have multiple subscribers to this.
So, I know the Retrofit Single has to be converted to a proper Observable stream and not just an onNext/onComplete like a normal Single.toObservable would, but I don't know how to requery the API and push the value back out to my previous subscribers using only the Single from Retrofit.
Right now, I do:
fun request(): Observable<Foo> {
if (behaviorSubject.value == defaultObject) {
API
.request()
.onErrorReturn(defaultObject)
.subscribe(behaviorSubject)
}
return behaviorSubject
}
But I know that calling subscribe is violating Rx chaining, so I'm trying to figure out how to get rid of that.
retrofit2 rx-java2
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
add a comment |
I'm using Retrofit to make an API call, which returns a Single, and I use onErrorReturn to convert any exceptions to a default object. I want consumers to see the current value, but if the current value is the default object, I want to try to requery the API and send that result out in addition. To complicate things, I might have multiple subscribers to this.
So, I know the Retrofit Single has to be converted to a proper Observable stream and not just an onNext/onComplete like a normal Single.toObservable would, but I don't know how to requery the API and push the value back out to my previous subscribers using only the Single from Retrofit.
Right now, I do:
fun request(): Observable<Foo> {
if (behaviorSubject.value == defaultObject) {
API
.request()
.onErrorReturn(defaultObject)
.subscribe(behaviorSubject)
}
return behaviorSubject
}
But I know that calling subscribe is violating Rx chaining, so I'm trying to figure out how to get rid of that.
retrofit2 rx-java2
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
add a comment |
I'm using Retrofit to make an API call, which returns a Single, and I use onErrorReturn to convert any exceptions to a default object. I want consumers to see the current value, but if the current value is the default object, I want to try to requery the API and send that result out in addition. To complicate things, I might have multiple subscribers to this.
So, I know the Retrofit Single has to be converted to a proper Observable stream and not just an onNext/onComplete like a normal Single.toObservable would, but I don't know how to requery the API and push the value back out to my previous subscribers using only the Single from Retrofit.
Right now, I do:
fun request(): Observable<Foo> {
if (behaviorSubject.value == defaultObject) {
API
.request()
.onErrorReturn(defaultObject)
.subscribe(behaviorSubject)
}
return behaviorSubject
}
But I know that calling subscribe is violating Rx chaining, so I'm trying to figure out how to get rid of that.
retrofit2 rx-java2
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
I'm using Retrofit to make an API call, which returns a Single, and I use onErrorReturn to convert any exceptions to a default object. I want consumers to see the current value, but if the current value is the default object, I want to try to requery the API and send that result out in addition. To complicate things, I might have multiple subscribers to this.
So, I know the Retrofit Single has to be converted to a proper Observable stream and not just an onNext/onComplete like a normal Single.toObservable would, but I don't know how to requery the API and push the value back out to my previous subscribers using only the Single from Retrofit.
Right now, I do:
fun request(): Observable<Foo> {
if (behaviorSubject.value == defaultObject) {
API
.request()
.onErrorReturn(defaultObject)
.subscribe(behaviorSubject)
}
return behaviorSubject
}
But I know that calling subscribe is violating Rx chaining, so I'm trying to figure out how to get rid of that.
retrofit2 rx-java2
retrofit2 rx-java2
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
asked Nov 16 '18 at 20:42
Heath BordersHeath Borders
20.5k9101195
20.5k9101195
add a comment |
add a comment |
1 Answer
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thank you for the interesting scenario. Here's a solution which I believe covers your requirements. It is longer than your solution but should be safe when it comes to multiple subscriptions.
// subscribe to this observable with one or more subscribers
val requestObservable = replayAndRetry(API.request(), defaultObject)
private fun <T> replayAndRetry(request: Single<T>, defaultValue: T): Observable<T> {
val responses = BehaviorSubject.create<T>()
val initialRequest = request
.onErrorReturnItem(defaultValue)
.doOnSuccess(responses::onNext)
.ignoreElement()
.cache() // run the initial request at most once
val retryWhenNecessary = Maybe
.fromCallable { if (responses.value == defaultValue) true else null }
.flatMapCompletable { request
.doOnSuccess(responses::onNext)
.ignoreElement()
.onErrorComplete() // subject already has the default value
}
.toObservable<T>().share() // avoid multiple simultaneous retries
return responses // source for all responses
.mergeWith(initialRequest) // will run once and then complete
.mergeWith(retryWhenNecessary) // will check for default item on every subscription
// will not run simultaneous retries
}
answered Feb 12 at 16:45
laengerlaenger
5401616
Thanks very much! I need to investigate this further to understand everything. I'm not familiar withmergeWith.
– Heath Borders
Feb 12 at 18:59
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
thank you for the interesting scenario. Here's a solution which I believe covers your requirements. It is longer than your solution but should be safe when it comes to multiple subscriptions.
// subscribe to this observable with one or more subscribers
val requestObservable = replayAndRetry(API.request(), defaultObject)
private fun <T> replayAndRetry(request: Single<T>, defaultValue: T): Observable<T> {
val responses = BehaviorSubject.create<T>()
val initialRequest = request
.onErrorReturnItem(defaultValue)
.doOnSuccess(responses::onNext)
.ignoreElement()
.cache() // run the initial request at most once
val retryWhenNecessary = Maybe
.fromCallable { if (responses.value == defaultValue) true else null }
.flatMapCompletable { request
.doOnSuccess(responses::onNext)
.ignoreElement()
.onErrorComplete() // subject already has the default value
}
.toObservable<T>().share() // avoid multiple simultaneous retries
return responses // source for all responses
.mergeWith(initialRequest) // will run once and then complete
.mergeWith(retryWhenNecessary) // will check for default item on every subscription
// will not run simultaneous retries
}
answered Feb 12 at 16:45
laengerlaenger
5401616
Thanks very much! I need to investigate this further to understand everything. I'm not familiar withmergeWith.
– Heath Borders
Feb 12 at 18:59
add a comment |
thank you for the interesting scenario. Here's a solution which I believe covers your requirements. It is longer than your solution but should be safe when it comes to multiple subscriptions.
// subscribe to this observable with one or more subscribers
val requestObservable = replayAndRetry(API.request(), defaultObject)
private fun <T> replayAndRetry(request: Single<T>, defaultValue: T): Observable<T> {
val responses = BehaviorSubject.create<T>()
val initialRequest = request
.onErrorReturnItem(defaultValue)
.doOnSuccess(responses::onNext)
.ignoreElement()
.cache() // run the initial request at most once
val retryWhenNecessary = Maybe
.fromCallable { if (responses.value == defaultValue) true else null }
.flatMapCompletable { request
.doOnSuccess(responses::onNext)
.ignoreElement()
.onErrorComplete() // subject already has the default value
}
.toObservable<T>().share() // avoid multiple simultaneous retries
return responses // source for all responses
.mergeWith(initialRequest) // will run once and then complete
.mergeWith(retryWhenNecessary) // will check for default item on every subscription
// will not run simultaneous retries
}
answered Feb 12 at 16:45
laengerlaenger
5401616
Thanks very much! I need to investigate this further to understand everything. I'm not familiar withmergeWith.
– Heath Borders
Feb 12 at 18:59
add a comment |
thank you for the interesting scenario. Here's a solution which I believe covers your requirements. It is longer than your solution but should be safe when it comes to multiple subscriptions.
// subscribe to this observable with one or more subscribers
val requestObservable = replayAndRetry(API.request(), defaultObject)
private fun <T> replayAndRetry(request: Single<T>, defaultValue: T): Observable<T> {
val responses = BehaviorSubject.create<T>()
val initialRequest = request
.onErrorReturnItem(defaultValue)
.doOnSuccess(responses::onNext)
.ignoreElement()
.cache() // run the initial request at most once
val retryWhenNecessary = Maybe
.fromCallable { if (responses.value == defaultValue) true else null }
.flatMapCompletable { request
.doOnSuccess(responses::onNext)
.ignoreElement()
.onErrorComplete() // subject already has the default value
}
.toObservable<T>().share() // avoid multiple simultaneous retries
return responses // source for all responses
.mergeWith(initialRequest) // will run once and then complete
.mergeWith(retryWhenNecessary) // will check for default item on every subscription
// will not run simultaneous retries
}
answered Feb 12 at 16:45
laengerlaenger
5401616
thank you for the interesting scenario. Here's a solution which I believe covers your requirements. It is longer than your solution but should be safe when it comes to multiple subscriptions.
// subscribe to this observable with one or more subscribers
val requestObservable = replayAndRetry(API.request(), defaultObject)
private fun <T> replayAndRetry(request: Single<T>, defaultValue: T): Observable<T> {
val responses = BehaviorSubject.create<T>()
val initialRequest = request
.onErrorReturnItem(defaultValue)
.doOnSuccess(responses::onNext)
.ignoreElement()
.cache() // run the initial request at most once
val retryWhenNecessary = Maybe
.fromCallable { if (responses.value == defaultValue) true else null }
.flatMapCompletable { request
.doOnSuccess(responses::onNext)
.ignoreElement()
.onErrorComplete() // subject already has the default value
}
.toObservable<T>().share() // avoid multiple simultaneous retries
return responses // source for all responses
.mergeWith(initialRequest) // will run once and then complete
.mergeWith(retryWhenNecessary) // will check for default item on every subscription
// will not run simultaneous retries
}
answered Feb 12 at 16:45
laengerlaenger
5401616
answered Feb 12 at 16:45
laengerlaenger
5401616
answered Feb 12 at 16:45
laengerlaenger
5401616
answered Feb 12 at 16:45
laengerlaenger
5401616
5401616
Thanks very much! I need to investigate this further to understand everything. I'm not familiar withmergeWith.
– Heath Borders
Feb 12 at 18:59
add a comment |
Thanks very much! I need to investigate this further to understand everything. I'm not familiar withmergeWith.
– Heath Borders
Feb 12 at 18:59
Thanks very much! I need to investigate this further to understand everything. I'm not familiar with
mergeWith.– Heath Borders
Feb 12 at 18:59
Thanks very much! I need to investigate this further to understand everything. I'm not familiar with
mergeWith.– Heath Borders
Feb 12 at 18:59
add a comment |
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