I'm making a network request inside a Repository class in my Android app. I'm doing this for learning purposes, so I'm trying to understand, without using RXJava, how would I update the UI all the way from my Repository?
The trail of calls goes like so MainActivity -> Presenter -> Interactor -> Repository -> Network
And here is my code in the repository
WeatherRepository {
WeatherNetwork network = new WeatherNetwork();
public CurrentWeather getCurrentWeather(float lat, float lng) {
network.getDailyWeather(lat, lng, new Callback() {
#Override
public void onFailure(Request request, IOException e) {
}
#Override
public void onResponse(Response response) throws IOException {
try{
String jsonData = response.body().string();
if (response.isSuccessful()) {
CurrentWeather currentWeather = getCurrentWeatherData(jsonData);
}
} catch(JSONException e) {
Log.d("DWPresen" + " JSONEXCEPTION", e.getMessage());
} catch(IOException e){
Log.d("DWPresent" + " IOEXCEPTION", e.getMessage());
}
}
});
}
}
Imho there are two classical ways to do such a thing:
One way would be to pass a callback object down to the repository and call the callback action when you get your response.
The second (and imho more elegant) way would be to use local broadcasts in your app. They can be used to transfer messages (like if something happened in your service and you want to notify other threads - like the UI thread - about it.)
There are quite a lot of tutorials about (local) broadcasts in android. Normal broadcasts are used to communicate between apps (and between the system and an app), while local broadcasts can be used to just send information within your app.
There is a library called EventBus that works very well with MVP structure.
Briefly, it passes the event(an object with data) from one class to another. In your case, you can pass an event with CurrentWeather object inside of it from Repository to Presenter and then update UI.
Related
Here is my current code. The problem with this code is I need to wait get the data sequentially. The loading time is poor because of this. I want to use something like .enqueue() to get asynchronously several data at once, but I want to wait until I get all the data before continuing the process. Is it possible to do it with Retrofit?
List<Data> datas = new ArrayList<>();
for (long dataId : mDataIds) {
Response<T> response = resource.getData(dataId).execute();
if (response.isSuccessful()) {
datas.add(data.body());
}
}
//do something else
You can solve this problem very elegantly using RxJava.
If you never heard of RxJava before, it is a solution to many of your problems.
If you don't use java8 or retrolambda I recommend you to start using it, as it makes working with RxJava a piece of cake.
Anyway here's what you need to do:
// 1. Stream each value from mDataIds
Observable.from(mDataIds)
// 2. Create a network request for each of the data ids
.flatMap(dataId -> resource.getData(dataId))
// 3. Collect responses to list
.toList()
// Your data is ready
.subscribe(datas -> {}, throwable -> {});
1) First add RxJava2 dependencies to your project
2) Define retrofit api interface methods which return RxJava observable types
public interface DataApi {
#GET("dataById/")
Observable<Data> getData(#Query("id") String id);
}
3) Call api passing input data like below.
Observable.fromIterable(idList).subscribeOn(Schedulers.computation())
.flatMap(id -> {
return retrofitService.getData(id).subscribeOn(Schedulers.io());
}).toList().
.observeOn(AndroidSchedulers.mainThread()).subscribe( listOfData -> {// do further processing }, error -> { //print errors} );
For reference : http://www.zoftino.com/retrofit-rxjava-android-example
Define interface with callback Model type.
public interface LoginService {
#GET("/login")
Call<List<Login>> getLogin();
}
In you calling method override the callback method.
LoginService loginService = ServiceGenerator.createService(LoginService.class);
Call<List<Login>> call = loginService.getLogin();
call.enqueue(new Callback<List<Login>>() {
#Override
public void onResponse(Call<List<Login>> call, Response<List<Login>> response) {
if (response.isSuccessful()) {
// Login successful
} else {
// error response, no access to resource?
}
}
#Override
public void onFailure(Call<List<Login>> call, Throwable t) {
// something went completely south (like no internet connection)
Log.d("Error", t.getMessage());
}
}
I would recommend using RxJava and try it. You have something called FlatMap to combine the results.
To Start here is the tutorial start for RxJava2 and Retrofit2.
i am building my app on android repository by Fernando Cejas and i have a problem with subscribing to observable after calling dispose.
When i come to dashboard, i call method subscribeOnUserMessages.execute(new Subscriber(), new Params(token)), which is method in UseCase class
public void execute(DisposableObserver<T> observer, Params params) {
Preconditions.checkNotNull(observer);
final Observable<T> observable = this.buildUseCaseObservable(params)
.subscribeOn(Schedulers.from(threadExecutor))
.observeOn(postExecutionThread.getScheduler());
addDisposable(observable.subscribeWith(observer));
}
In child class SubscribeOnUserMessages i simply call repository like this
return messageRepository.subscribeOnUserMessages(params);
In my socket implementation i create like this
return Observable.create(emitter -> {
if (!isThereInternetConnection()) {
Timber.w("Network connection exception");
emitter.onError(new NetworkConnectionException());
return;
}
/*
* Open socket if not opened
*/
openSocket(params.getToken());
String channelName = CHANNEL_PRIVATE_USER + params.getAuthenticated().getUuid();
if (subscribedChannels.contains(channelName)) {
Timber.d("Channel %s is already subscribed", channelName);
return;
}
JSONObject auth;
try {
auth = createAuthJson(CHANNEL, channelName, params.getToken());
} catch (JSONException e) {
Timber.e("Couldn't create auth json");
emitter.onError(e);
return;
}
mSocket.emit(SUBSCRIBE, auth);
Timber.d("Emitted subscribe with channel: %s ", CHANNEL_PRIVATE_USER + params.getAuthenticated().getUuid());
subscribedChannels.add(CHANNEL_PRIVATE_USER + params.getAuthenticated().getUuid());
Timber.d("Subscribing on event: %s\n with user: %s", EVENT_USER_NEW_MESSAGE, params.getAuthenticated().getUuid());
if (mSocket.hasListeners(EVENT_USER_NEW_MESSAGE)) {
Timber.v("Socket already has listener on event: %s", EVENT_USER_NEW_MESSAGE);
return;
}
mSocket.on(EVENT_USER_NEW_MESSAGE, args -> {
if (args[1] == null) {
emitter.onError(new EmptyResponseException());
}
Timber.d("Event - %s %s", EVENT_USER_NEW_MESSAGE, args[1].toString());
try {
MessageEntity messageEntity = messageEntityJsonMapper.transform(args[1]);
emitter.onNext(messageEntity);
} catch (JSONException e) {
Timber.e(e, "Could not parse message json");
emitter.onError(e);
}
});
});
Symptoms are that first time i subscribe everything is going through to presentation layer. When i dispose after going to second screen and come back i only see logs coming to socket implementation, but not going through.
My question is: Is there a method for subscribing to same observable again? I've already tried to save that observable in my use case in singleton and subscribe to that observable, didn't help.
Without additional info and details regrading socket implementation it is hard to spot the problem exactly, but, from the code you've posted, you don't have dispose logic, so while you might properly call dispose() to the Observable at the correct lifecycle event, your socket will actually stay open, and it might not got disconnected/closed properly ever.
That might lead to a problems opening and connecting to the socket at the 2nd time, as you might try to reopen already open socket and depends on your internal socket impl that might be a problem.
(I can see in the comment that openSocket if not already opened, but still there might be problem elsewhere calling some method on the socket multiple times or setting listeners, again depends on the socket impl)
As a general guidelines, you should add dispose logic using emitter.setCancellable()/emitter.setDisposable() in order to dispose properly the socket resources when you no longer need them, thus - when applying subscribe again (whether the same object or not) will invoke your subscription logic again that will reopen the socket and listen to it.
It is not clear to me if you like to keep the socket open when you moving to a different screen (I don't think it is a good practice, as you will keep this resource open and might never get back to the screen again to use it), but if that's the case as #Phoenix Wang mentioned, you can use publish kind operators to multicast the Observable, so every new Subscriber will not try to reopen the socket (i.e. invoking the subscription logic) but will just get notify about messages running in the already opened socket.
Following the topic discussed here. I'm coding an Android App using the Clean Architecture. I've an Interactor that takes care of retriving the User's feed data. The flow is like this:
I must fetch the Feed data from the a Repository which calls a Retrofit's service to do the API call.
If something goes wrong I've to fetch the feed data from a FeedCache that internally works with Sqlite.
I've to merge this feed collection with another bunch of feeds from another cache called PendingPostCache. This cache contains all the articles that the user couldn't post (because something went wrong, didn't had internet connection, etc.)
My FeedCache and PendingPostCache both work with Sqlite. Botch can throw DBExceptions if something went wrong. My FeedRepository the ones that makes the requests against the server-side can also throw exceptions if something goes wrong (ServerSideException).
Here's the whole code from my Interactor:
mFeedRepository.getFeed(offset, pageSize) //Get items from the server-side
.onErrorResumeNext(mFeedCache.getFeed(userSipid)) //If something goes wrong take it from cache
.mergeWith(mPendingPostCache.getAllPendingPostsAsFeedItems(user)) //Merge the response with the pending posts
.subscribe(new DefaultSubscriber<List<BaseFeedItem>>() {
#Override
public void onNext(List<BaseFeedItem> baseFeedItems) {
callback.onFeedFetched(baseFeedItems);
}
#Override
public void onError(Throwable e) {
if (e instanceof ServerSideException) {
//Handle the http error
} else if (e instanceof DBException) {
//Handle the database cache error
} else {
//Handle generic error
}
}
});
I don't like having those instanceof. I'm thinking on creating a custom subscriber, something called like MyAppSubscriber, which implements the onError method, makes those instanceof comparations, and execute some methods called onServerSideError(), onDBError(). That way the code is going te be a lot cleaner and I can spare writing that instanceof boilerplate code. Has someone a better idea about how to approach this issue? Some way to avoid the custom Subscriber?
Just use composition:
public <T,E> Function<Throwable, Observable<T>> whenExceptionIs(Class<E> what, Function<E, Observable<T>> handler) {
return t -> {
return what.isInstance(t) ? handler.apply(what.cast(t)) : Observable.error(t);
};
}
Then you use it normally :
Observable.from(...).flatMap(...)
.onErrorResumeNext(whenExceptionIs(ServerSideException.class, e-> Observable.empty()))
.onErrorResumeNext(whenExceptionIs(DBException.class, e-> ...))
You can even abstract all that in one method:
public <T> Transformer<T, T> errorHandling() {
return src -> src
.onErrorResumeNext(whenExceptionIs(ServerSideException.class, e-> Observable.empty()))
.onErrorResumeNext(whenExceptionIs(DBException.class, e-> ...));
}
Observable.from(...).flatMap(...)
.compose(errorHandling())
.subscribe();
should i put my retrofit calls inside and Android Service class?
for my application iam calling retrofit inside in some classes for example like below
Call<ArrayList<CantItem>> mycall = retrofitcalls.getCanteenItems("url.php", urldatamap);
mycall.enqueue(new Callback<ArrayList<CantItem>>() {
#Override
public void onResponse(Response<ArrayList<CantItem>> response, Retrofit retrofit) {
int code = response.code();
Log.d("code ", String.valueOf(code));
if (code == 200 || code == 201) {
ArrayList<CantItem> cantitems = response.body();
Log.d("retrieved", "returned items");
savedToSharedPrefs(createString(cantitems));
cantmap = createMap(cantitems);
presenter.updateView(cantmap);
}
}
#Override
public void onFailure(Throwable t) {
Log.d("couldnt retrieve", "failure");
}
});
I was wondering should i put this call inside an Android Service class? as my retrofit call runs asynchronously anyway? Every tutorial ive seen seems to run it in either classes or activities. I haven't seen anyone using a service. Im not 100% sure what the best approach is at present. thanks
It really depends on your requirements. Do you need the result of the webservice call even if your application killed?
If yes, then put it into a service.
If not then just starts something from your Activity.
I'm building a 2 Player game on Android. The game works turnwise, so player 1 waits until player 2 made his input and vice versa. I have a webserver where I run an API with the Slim Framework. On the clients I use Retrofit. So on the clients I would like to poll my webserver (I know it's not the best approach) every X seconds to check whether there was an input from player 2 or not, if yes change UI (the gameboard).
Dealing with Retrofit I came across RxJava. My problem is to figure out whether I need to use RxJava or not? If yes, are there any really simple examples for polling with retrofit? (Since I send only a couple of key/value pairs) And if not how to do it with retrofit instead?
I found this thread here but it didn't help me too because I still don't know if I need Retrofit + RxJava at all, are there maybe easier ways?
Let's say the interface you defined for Retrofit contains a method like this:
public Observable<GameState> loadGameState(#Query("id") String gameId);
Retrofit methods can be defined in one of three ways:
1.) a simple synchronous one:
public GameState loadGameState(#Query("id") String gameId);
2.) one that take a Callback for asynchronous handling:
public void loadGameState(#Query("id") String gameId, Callback<GameState> callback);
3.) and the one that returns an rxjava Observable, see above. I think if you are going to use Retrofit in conjunction with rxjava it makes the most sense to use this version.
That way you could just use the Observable for a single request directly like this:
mApiService.loadGameState(mGameId)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<GameState>() {
#Override
public void onNext(GameState gameState) {
// use the current game state here
}
// onError and onCompleted are also here
});
If you want to repeatedly poll the server using you can provide the "pulse" using versions of timer() or interval():
Observable.timer(0, 2000, TimeUnit.MILLISECONDS)
.flatMap(mApiService.loadGameState(mGameId))
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<GameState>() {
#Override
public void onNext(GameState gameState) {
// use the current game state here
}
// onError and onCompleted are also here
}).
It is important to note that I am using flatMap here instead of map - that's because the return value of loadGameState(mGameId) is itself an Observable.
But the version you are using in your update should work too:
Observable.interval(2, TimeUnit.SECONDS, Schedulers.io())
.map(tick -> Api.ReceiveGameTurn())
.doOnError(err -> Log.e("Polling", "Error retrieving messages" + err))
.retry()
.observeOn(AndroidSchedulers.mainThread())
.subscribe(sub);
That is, if ReceiveGameTurn() is defined synchronously like my 1.) above, you would use map instead of flatMap.
In both cases the onNext of your Subscriber would be called every two seconds with the latest game state from the server. You can process them one after another of limit the emission to a single item by inserting take(1) before subscribe().
However, regarding the first version: A single network error would be first delivered to onError and then the Observable would stop emitting any more items, rendering your Subscriber useless and without input (remember, onError can only be called once). To work around this you could use any of the onError* methods of rxjava to "redirect" the failure to onNext.
For example:
Observable.timer(0, 2000, TimeUnit.MILLISECONDS)
.flatMap(new Func1<Long, Observable<GameState>>(){
#Override
public Observable<GameState> call(Long tick) {
return mApiService.loadGameState(mGameId)
.doOnError(err -> Log.e("Polling", "Error retrieving messages" + err))
.onErrorResumeNext(new Func1<Throwable, Observable<GameState>(){
#Override
public Observable<GameState> call(Throwable throwable) {
return Observable.emtpy());
}
});
}
})
.filter(/* check if it is a valid new game state */)
.take(1)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<GameState>() {
#Override
public void onNext(GameState gameState) {
// use the current game state here
}
// onError and onCompleted are also here
}).
This will every two seconds:
* use Retrofit to get the current game state from the server
* filter out invalid ones
* take the first valid one
* and the unsubscribe
In case of an error:
* it will print an error message in doOnNext
* and otherwise ignore the error: onErrorResumeNext will "consume" the onError-Event (i.e. your Subscriber's onError will not be called) and replaces it with nothing (Observable.empty()).
And, regarding the second version: In case of a network error retry would resubscribe to the interval immediately - and since interval emits the first Integer immediately upon subscription the next request would be sent immediately, too - and not after 3 seconds as you probably want...
Final note: Also, if your game state is quite large, you could also first just poll the server to ask whether a new state is available and only in case of a positive answer reload the new game state.
If you need more elaborate examples, please ask.
UPDATE: I've rewritten parts of this post and added more information in between.
UPDATE 2: I've added a full example of error handling with onErrorResumeNext.
Thank you, I finally made it in a similar way based the post I referred to in my question. Here's my code for now:
Subscriber sub = new Subscriber<Long>() {
#Override
public void onNext(Long _EmittedNumber)
{
GameTurn Turn = Api.ReceiveGameTurn(mGameInfo.GetGameID(), mGameInfo.GetPlayerOneID());
Log.d("Polling", "onNext: GameID - " + Turn.GetGameID());
}
#Override
public void onCompleted() {
Log.d("Polling", "Completed!");
}
#Override
public void onError(Throwable e) {
Log.d("Polling", "Error: " + e);
}
};
Observable.interval(3, TimeUnit.SECONDS, Schedulers.io())
// .map(tick -> Api.ReceiveGameTurn())
// .doOnError(err -> Log.e("Polling", "Error retrieving messages" + err))
.retry()
.subscribe(sub);
The problem now is that I need to terminate emitting when I get a positive answer (a GameTurn). I read about the takeUntil method where I would need to pass another Observable which would emit something once which would trigger the termination of my polling. But I'm not sure how to implement this.
According to your solution, your API method returns an Observable like it is shown on the Retrofit website. Maybe this is the solution? So how would it work?
UPDATE:
I considered #david.miholas advices and tried his suggestion with retry and filter. Below you can find the code for the game initialization. The polling should work identically: Player1 starts a new game -> polls for opponent, Player2 joins the game -> server sends to Player1 opponent's ID -> polling terminated.
Subscriber sub = new Subscriber<String>() {
#Override
public void onNext(String _SearchOpponentResult) {}
#Override
public void onCompleted() {
Log.d("Polling", "Completed!");
}
#Override
public void onError(Throwable e) {
Log.d("Polling", "Error: " + e);
}
};
Observable.interval(3, TimeUnit.SECONDS, Schedulers.io())
.map(tick -> mApiService.SearchForOpponent(mGameInfo.GetGameID()))
.doOnError(err -> Log.e("Polling", "Error retrieving messages: " + err))
.retry()
.filter(new Func1<String, Boolean>()
{
#Override
public Boolean call(String _SearchOpponentResult)
{
Boolean OpponentExists;
if (_SearchOpponentResult != "0")
{
Log.e("Polling", "Filter " + _SearchOpponentResult);
OpponentExists = true;
}
else
{
OpponentExists = false;
}
return OpponentExists;
}
})
.take(1)
.subscribe(sub);
The emission is correct, however I get this log message on every emit:
E/Pollingļ¹ Error retrieving messages: java.lang.NullPointerException
Apperently doOnError is triggered on every emit. Normally I would get some Retrofit debug logs on every emit which means that mApiService.SearchForOpponent won't get called. What do I do wrong?