RxJava unsubscribeOn with recursive call not in the right thread

RxJava unsubscribeOn with recursive call not in the right thread - android

I've built an headless webview in an Android application for scrape an URL from a webpage. Every time I retrieve an URL I may need to redoing the scraping in the webpage with this URL. I'm using RxJava to handle these operations concurrently, and I'm using the flatMap function to make a recursive call.
The problem is that I need to dispose the WebView in the mainThread, so I tried to add .unsubscribeOn(AndroidSchedulers.mainThread()) but it seems it doesn't work, and the dispose() method in HeadlessRequest is called in the last thread I called observeOn(Schedulers.computation()). What should I change to execute the dispose() method in the mainThread?
This is my code:
HeadlessRequest
public class HeadlessRequest implements Disposable {
...
private class HeadlessWebView extends WebView {
...
private void destroyWebView() {
this.removeAllViews();
this.clearCache(false);
this.loadUrl("about:blank");
this.onPause();
this.removeAllViews();
this.destroy();
this.isDisposed = true;
}
}
#Override
public void dispose() {
// This doesn't print the mainThread id
Log.d(TAG, "Disposing on thread " + Thread.currentThread().getId());
this.webView.destroyWebView();
this.webView = null;
}
#Override
public boolean isDisposed() {
return (this.webView == null || this.webView.isDisposed);
}
}
NetworkUtils
public static Single<Document> downloadPageHeadless(final String url, final int delay, final Context context) {
return Single.create((SingleEmitter<Document> emitter) -> {
try {
emitter.setDisposable(new HeadlessRequest(url, USER_AGENT, delay, context, emitter::onSuccess, emitter::onError));
} catch (Exception e) {
emitter.onError(e);
}
}).unsubscribeOn(AndroidSchedulers.mainThread()) // It MUST be executed on the mainThread
.subscribeOn(AndroidSchedulers.mainThread());
}
ServerService
private static Single<String> resolveRecursive(String url, Context context) {
Server server = getServerInstance(url, context);
if (server == null) {
return Single.error(new UnsupportedOperationException("Server for " + url + " not supported"));
} else if (server.isVideo()) {
return server.resolve(url, context); // This method return a Single with observeOn(Schedulers.computation())
} else {
return server.resolve(url, context)
.observeOn(Schedulers.computation())
.flatMap(resolvedUrl -> resolveRecursive(resolvedUrl, context));
}
}
public static Single<String> resolveURL(String url, Context context) {
return resolveRecursive(url, context)
.observeOn(AndroidSchedulers.mainThread());
}

At the end I found another method to dispose the webview in the mainThread without RxJava. I've used the post method of the WebView.
private void destroyWebView() {
this.post(() -> {
this.removeAllViews();
this.clearCache(false);
this.loadUrl("about:blank");
this.onPause();
this.removeAllViews();
this.destroy();
this.isDisposed = true;
});
}

Related

How to Manage State with RxJava in Android using Java (Not Kotlin)

I am attempting to developed an Android application based on the following talk presented by Jake Wharton
The State of Managing State with RxJava
21 March 2017 – Devoxx (San Jose, CA, USA)
Jake promised a part 2 and/or GITHUB example which I am unable to find (If indeed either exists)
At a high level I can follow/understand the majority of the above talk.
However I have the following questions.
I can see how employing UiEvent, UiModel, Action, and Result keeps concerns separated.
What I am confused about is the following:-
The diagram on slide 194 shows the "flow/stream" of Observables as
Android Device -----> Observable<UiEvent> -----> <application code> -----> Observable<Action> -----> {Backend}
{Backend} -----> Observable<Result> -----> <application code> -----> Observable<UiModel> -----> Android Device
Slide 210 contains this code snippet, showing how the Result(s) stream is "scan"ned into UiModel
SubmitUiModel initialState = SubmitUiModel.idle();
Observable<Result> results = /* ... */;
Observable<SubmitUiModel> uiModels = results.scan(initialState, (state, result) -> {
if (result == CheckNameResult.IN_FLIGHT
|| result == SubmitResult.IN_FLIGHT)
return SubmitUiModel.inProgress();
if (result == CheckNameResult.SUCCESS)
return SubmitUiModel.idle();
if (result == SubmitResult.SUCCESS)
return SubmitUiModel.success();
// TODO handle check name and submit failures...
throw new IllegalArgumentException("Unknown result: " + result);
});
and the final code snippet on slide 215, the code snippet resembles this:-
ObservableTransformer<SubmitAction, SubmitResult> submit =
actions -> actions.flatMap(action -> service.setName(action.name)
.map(response -> SubmitResult.SUCCESS)
.onErrorReturn(t -> SubmitResult.failure(t.getMessage()))
.observeOn(AndroidSchedulers.mainThread())
.startWith(SubmitResult.IN_FLIGHT));
ObservableTransformer<CheckNameAction, CheckNameResult> checkName =
actions -> actions.switchMap(action -> action
.delay(200, MILLISECONDS, AndroidSchedulers.mainThread())
.flatMap(action -> service.checkName(action.name))
.map(response -> CheckNameResult.SUCCESS)
.onErrorReturn(t -> CheckNameResult.failure(t.getMessage()))
.observeOn(AndroidSchedulers.mainThread())
.startWith(CheckNameResult.IN_FLIGHT));
which illustrates conversion from Action(s) to Result(s)
what am I missing from this talk/slide-deck on how to combine the UiEvent/UiModel to the Action/Result stream?
The stream is driven by UiEvents
How do you complete the flow from UiEvent(s) to Action back to Result then finally UiModel?
UPDATE
Using the Star Wars API I have taken the following approach
I use my UI Events to drive the transformation between UI Events to Results via Actions, then scan the results to map back to UI Model.
Heres my classes and code:-
ACTION CLASSES
==============
public abstract class Action<T> {
Api service = Service.instance();
final T data;
public Action(final T data) {
this.data = data;
}
public T getData() {
return data;
}
public abstract Observable<Response<String>> execute();
}
public class CheckCharacterAction extends Action<String> {
public CheckCharacterAction(final String characterName) {
super(characterName);
}
#Override
public Observable<Response<String>> execute() {
return service.peopleSearch(getData());
}
}
public class CheckFilmAction extends Action<String> {
public CheckFilmAction(final String filmTitle) {
super(filmTitle);
}
#Override
public Observable<Response<String>> execute() {
return service.filmSearch(getData());
}
}
public class SearchAction extends Action<String> {
public SearchAction(final String search) {
super(search);
}
#Override
public Observable<Response<String>> execute() {
return service.filmSearch(getData());
}
}
EVENT CLASSES
=============
public abstract class UiEvent<T> {
private final T data;
public UiEvent(final T data) {
this.data = data;
}
public T getData() {
return data;
}
}
public class CharacterUiEvent extends UiEvent<String> {
public CharacterUiEvent(final String name) {
super(name);
}
}
public class FilmUiEvent extends UiEvent<String> {
public FilmUiEvent(final String title) {
super(title);
}
}
public class SearchUiEvent extends UiEvent<String> {
public SearchUiEvent(final String data) {
super(data);
}
}
UI MODEL CLASSES
================
public class UiModel<T> {
public final boolean isProgress;
public final String message;
public final boolean isSuccess;
public T data;
public UiModel(final boolean isProgress) {
this.isProgress = isProgress;
this.message = null;
this.isSuccess = false;
this.data = null;
}
public UiModel(final T data) {
this.isProgress = false;
this.message = null;
this.isSuccess = true;
this.data = data;
}
public UiModel(final String message) {
this.isProgress = false;
this.message = message;
this.isSuccess = false;
this.data = null;
}
public UiModel(final boolean isProgress, final String message, final boolean isSuccess, final T data) {
this.isProgress = isProgress;
this.message = message;
this.isSuccess = isSuccess;
this.data = data;
}
}
public class CharacterUiModel extends UiModel<JsonData> {
public CharacterUiModel(final boolean isProgress) {
super(isProgress);
}
public CharacterUiModel(final JsonData data) {
super(data);
}
public CharacterUiModel(final String message) {
super(message);
}
public CharacterUiModel(final boolean isProgress, final String message, final boolean isSuccess, final JsonData data) {
super(isProgress, message, isSuccess, data);
}
public static CharacterUiModel inProgress() {
return new CharacterUiModel(true);
}
public static CharacterUiModel success(final JsonData data) {
return new CharacterUiModel(data);
}
public static CharacterUiModel failure(final String message) {
return new CharacterUiModel(message);
}
}
public class FilmUiModel extends UiModel<JsonData> {
public FilmUiModel(final boolean isProgress) {
super(isProgress);
}
public FilmUiModel(final JsonData data) {
super(data);
}
public FilmUiModel(final String message) {
super(message);
}
public FilmUiModel(final boolean isProgress, final String message, final boolean isSuccess, final JsonData data) {
super(isProgress, message, isSuccess, data);
}
public static FilmUiModel inProgress() {
return new FilmUiModel(true);
}
public static FilmUiModel success(final JsonData data) {
return new FilmUiModel(data);
}
public static FilmUiModel failure(final String message) {
return new FilmUiModel(message);
}
}
public class SearchUiModel extends UiModel<JsonData> {
private SearchUiModel(final boolean isProgress) {
super(isProgress);
}
private SearchUiModel(final JsonData data) {
super(data);
}
private SearchUiModel(final String message) {
super(message);
}
private SearchUiModel(final boolean isProgress, final String message, final boolean isSuccess, final JsonData data) {
super(isProgress, message, isSuccess, data);
}
public static SearchUiModel idle() {
return new SearchUiModel(false, null, false, null);
}
public static SearchUiModel inProgress() {
return new SearchUiModel(true);
}
public static SearchUiModel success(final JsonData data) {
return new SearchUiModel(data);
}
public static SearchUiModel failure(final String message) {
return new SearchUiModel(message);
}
}
RESULT CLASSES
==============
public abstract class Result<T> {
public enum LIFECYCLE {
DEPARTURE_LOUNGE,
IN_FLIGHT,
LANDED_SAFELY,
CRASHED_BURNED
}
final LIFECYCLE lifecycle;
final T data;
final String errorMessage;
public Result(final LIFECYCLE lifecycle, final T data, final String errorMessage) {
this.lifecycle = lifecycle;
this.data = data;
this.errorMessage = errorMessage;
}
public T getData() {
return data;
}
public String getErrorMessage() {
return errorMessage;
}
public LIFECYCLE getLifecycle() {
return lifecycle;
}
}
public class CharacterResult extends Result<JsonData> {
private CharacterResult(final LIFECYCLE lifecycle, final JsonData data, final String errorMessage) {
super(lifecycle, data, errorMessage);
}
private CharacterResult(final LIFECYCLE lifecycle) {
super(lifecycle, null, null);
}
public static CharacterResult departureLounge() {
return new CharacterResult(LIFECYCLE.DEPARTURE_LOUNGE);
}
public static CharacterResult inflight() {
return new CharacterResult(LIFECYCLE.IN_FLIGHT);
}
public static CharacterResult landedSafely(final JsonData data) {
return new CharacterResult(LIFECYCLE.LANDED_SAFELY, data, null);
}
public static CharacterResult crashedBurned(final String errorMessage) {
return new CharacterResult(LIFECYCLE.CRASHED_BURNED, null, errorMessage);
}
}
public class FilmResult extends Result<JsonData> {
private FilmResult(final LIFECYCLE lifecycle, final JsonData data, final String errorMessage) {
super(lifecycle, data, errorMessage);
}
private FilmResult(final LIFECYCLE lifecycle) {
super(lifecycle, null, null);
}
public static FilmResult departureLounge() {
return new FilmResult(LIFECYCLE.DEPARTURE_LOUNGE);
}
public static FilmResult inflight() {
return new FilmResult(LIFECYCLE.IN_FLIGHT);
}
public static FilmResult landedSafely(final JsonData data) {
return new FilmResult(LIFECYCLE.LANDED_SAFELY, data, null);
}
public static FilmResult crashedBurned(final String errorMessage) {
return new FilmResult(LIFECYCLE.CRASHED_BURNED, null, errorMessage);
}
}
public class SearchResult extends Result<JsonData> {
private SearchResult(final LIFECYCLE lifecycle, final JsonData data, final String errorMessage) {
super(lifecycle, data, errorMessage);
}
private SearchResult(final LIFECYCLE lifecycle) {
super(lifecycle, null, null);
}
public static SearchResult departureLounge() {
return new SearchResult(LIFECYCLE.DEPARTURE_LOUNGE);
}
public static SearchResult inflight() {
return new SearchResult(LIFECYCLE.IN_FLIGHT);
}
public static SearchResult landedSafely(final JsonData data) {
return new SearchResult(LIFECYCLE.LANDED_SAFELY, data, null);
}
public static SearchResult crashedBurned(final String errorMessage) {
return new SearchResult(LIFECYCLE.CRASHED_BURNED, null, errorMessage);
}
}
I then set up my Rx Streams as follows from my Activity onCreate() method:-
final Observable<SearchUiEvent> searchEvents = RxView.clicks(activityMainBinding.searchButton)
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(AndroidSchedulers.mainThread())
.map(ignored -> new SearchUiEvent(activityMainBinding.filmTitle.getText().toString()));
final Observable<FilmUiEvent> filmEvents = RxTextView.afterTextChangeEvents(activityMainBinding.filmTitle)
.skipInitialValue()
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(AndroidSchedulers.mainThread())
.delay(1000, MILLISECONDS, AndroidSchedulers.mainThread())
.map(text -> new FilmUiEvent(text.view().getText().toString()));
final Observable<CharacterUiEvent> characterEvents = RxTextView.afterTextChangeEvents(activityMainBinding.people)
.skipInitialValue()
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(AndroidSchedulers.mainThread())
.delay(200, MILLISECONDS, AndroidSchedulers.mainThread())
.map(text -> new CharacterUiEvent(text.view().getText().toString()));
/**
*
*/
final Observable<UiEvent> uiEvents = Observable.merge(searchEvents, filmEvents, characterEvents);
/*********
*
*/
final ObservableTransformer<SearchUiEvent, SearchResult> searchAction =
events -> events.flatMap(event -> new SearchAction(event.getData()).execute().subscribeOn(Schedulers.io()))
.map(response -> SearchResult.landedSafely(new JsonData(response.body())))
.onErrorReturn(throwable -> SearchResult.crashedBurned(throwable.getMessage()))
.startWith(SearchResult.inflight());
final ObservableTransformer<FilmUiEvent, FilmResult> filmAction =
events -> events.flatMap(event -> new CheckFilmAction(event.getData()).execute().subscribeOn(Schedulers.io()))
.map(response -> FilmResult.landedSafely(new JsonData(response.body())))
.onErrorReturn(throwable -> FilmResult.crashedBurned(throwable.getMessage()))
.startWith(FilmResult.inflight());
final ObservableTransformer<CharacterUiEvent, CharacterResult> characterAction =
events -> events.flatMap(event -> new CheckCharacterAction(event.getData()).execute().subscribeOn(Schedulers.io()))
.map(response -> CharacterResult.landedSafely(new JsonData(response.body())))
.onErrorReturn(throwable -> CharacterResult.crashedBurned(throwable.getMessage()))
.startWith(CharacterResult.inflight());
final ObservableTransformer<UiEvent, ? extends Result> whatever = events -> events.publish(shared -> Observable.merge(
shared.ofType(SearchUiEvent.class).compose(searchAction),
shared.ofType(CharacterUiEvent.class).compose(characterAction),
shared.ofType(FilmUiEvent.class).compose(filmAction)));
/**
*
*/
final UiModel initialState = SearchUiModel.idle();
final Observable<? extends Result> results = uiEvents.compose(whatever).doOnSubscribe(COMPOSITE_DISPOSABLE::add);
final Observable<UiModel> models = results.scan(initialState, (state, result) -> {
Log.e(TAG, "scan() state = " + state + " result = " + result);
if (result.getLifecycle().equals(SearchResult.LIFECYCLE.DEPARTURE_LOUNGE) ||
result.getLifecycle().equals(CharacterResult.LIFECYCLE.DEPARTURE_LOUNGE) ||
result.getLifecycle().equals(FilmResult.LIFECYCLE.DEPARTURE_LOUNGE)) {
return SearchUiModel.idle();
}
if (result.getLifecycle().equals(SearchResult.LIFECYCLE.IN_FLIGHT) ||
result.getLifecycle().equals(CharacterResult.LIFECYCLE.IN_FLIGHT) ||
result.getLifecycle().equals(FilmResult.LIFECYCLE.IN_FLIGHT)) {
return SearchUiModel.inProgress();
}
if (result.getLifecycle().equals(SearchResult.LIFECYCLE.LANDED_SAFELY) ||
result.getLifecycle().equals(CharacterResult.LIFECYCLE.LANDED_SAFELY) ||
result.getLifecycle().equals(FilmResult.LIFECYCLE.LANDED_SAFELY)) {
return SearchUiModel.success((JsonData) result.getData());
}
if (result.getLifecycle().equals(SearchResult.LIFECYCLE.CRASHED_BURNED) ||
result.getLifecycle().equals(CharacterResult.LIFECYCLE.CRASHED_BURNED) ||
result.getLifecycle().equals(FilmResult.LIFECYCLE.CRASHED_BURNED)) {
return SearchUiModel.failure(result.getErrorMessage());
}
return null;
});
models.doOnSubscribe(COMPOSITE_DISPOSABLE::add).subscribe(model -> report(model), throwable -> error(throwable));
As soon as my activity displays I get the following logs:-
2018-10-09 14:22:33.310 D/MainActivity: report() called with: model = [UiModel{isProgress=false, message='null', isSuccess=false, data=null}]
2018-10-09 14:22:33.311 E/MainActivity: scan() state = UiModel{isProgress=false, message='null', isSuccess=false, data=null} result = SearchResult{lifecycle=IN_FLIGHT, data=null, errorMessage='null'}
2018-10-09 14:22:33.311 D/MainActivity: report() called with: model = [UiModel{isProgress=true, message='null', isSuccess=false, data=null}]
2018-10-09 14:22:33.313 E/MainActivity: scan() state = UiModel{isProgress=true, message='null', isSuccess=false, data=null} result = CharacterResult{lifecycle=IN_FLIGHT, data=null, errorMessage='null'}
2018-10-09 14:22:33.313 D/MainActivity: report() called with: model = [UiModel{isProgress=true, message='null', isSuccess=false, data=null}]
2018-10-09 14:22:33.313 E/MainActivity: scan() state = UiModel{isProgress=true, message='null', isSuccess=false, data=null} result = FilmResult{lifecycle=IN_FLIGHT, data=null, errorMessage='null'}
2018-10-09 14:22:33.313 D/MainActivity: report() called with: model = [UiModel{isProgress=true, message='null', isSuccess=false, data=null}]
Im guessing I get these IN FLIGHT results due to my .startWith() statements.
When I either click my Search button or enter any text in my EditText views I see the following logs:-
2018-10-09 14:55:19.463 E/MainActivity: scan() state = UiModel{isProgress=false, message='null', isSuccess=true, data=com.test.model.JsonData#5e0b6f1} result = FilmResult{lifecycle=LANDED_SAFELY, data=com.test.model.JsonData#8ae4d86, errorMessage='null'}
2018-10-09 14:55:19.463 D/MainActivity: report() called with: model = [UiModel{isProgress=false, message='null', isSuccess=true, data=com.test.model.JsonData#8ae4d86}]
Why do I not see "IN FLIGHT" then "LANDED SAFELY"?
I only get "LANDED SAFELY"
Is my approach to transforming between UI Event -> Action -> Result -> UI Model anywhere close to what is described by Mr J Wharton?
Where have I gone wrong?
UPDATE (II)
My mistake was to not include all my downstream Rx within the .flatmap() operation.
CLARIFICATION
Does this pattern of UI Event ---> Action ---> Result ---> UI Model still apply for cases where there is no "Backend" as such? e.g. a Home screen could present the user with a number of options (buttons) to navigate to lower level screens within the application. The UI Event would be "Button Click" the UI Model would return with the associated Activity class to employ with the startActivity() method call.
How can I amalgamate the UI input events of a login screen into a single stream of UI events where I have two EditText fields (User Name and Password) and a Login Button.
I would want the button click UI event to contain the user name and user password entered. If I was using RxBinding to process the EditTexts and the Login button click I cannot see how I can combine these three Observables into my UI event stream and have the EditTexts validated to ensure they have data entered and then pass this user entered data to my back end login API (or maybe Google Sign In for example)

(I was adding a comment but it was too long)
I cannot help with the talks and so on presented by Jake. But regarding your last question:
Does this pattern of UI Event ---> Action ---> Result ---> UI Model
still apply for cases where there is no "Backend" as such?
It does, it is just that the backend is your application state repository.
In this kind of architecture there should only be one place of truth for your application: be it a backend, a local database, a combination of both or whatever solution is appropriate for your usecase.
Having that in mind your Action streams should modify the state either by doing calls to the backend, posting changes to a database or writing elements in the sharedSetting. Similarly, changes in your state should trigger sending Results down your streams.
The specific details would depend on what you use as a source of truth for your application.

DataFlow and State
It uses mainly Paco and Jake Wharton RxState idea plus added some more stuff.
To use UiEvent → Action, Result → UiModel transformers and always act
on a single state with the help of RxJava operators (Forming a single
stream of events, then based on their types handling actions with
different transformers, then combine results again, modifying the
state and then finally render it on the UI.
or not to use transformers and make it a little bit “simpler”.
So here is the “full” view model code without using any transformers:
class SomeViewModel(private val someRepository: SomeRepository): ViewModel() {
val uiEvents: PublishSubject<UiEvent> = PublishSubject.create()
val outputState: MutableLiveData<Result<UiState>> = MutableLiveData()
init {
uiEvents.subscribe {
when (it) {
is FirstEvent -> getSomeResultsFromRepo(it.id)
is SecondEvent -> handleSecondEvent()
}
}
}
fun getSomeResultsFromRepo(id: String) {
someRepository.getResult(id)
.map { UiState(it) }
.map { Result.success(it) }
.startWith(Result.loading())
.onErrorReturn { handleError(it) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe({
outputState.postValue(it)
})
}
fun handleSecondEvent() {
/* do something here */
someRepository.getSomeOtherResult()
.map { UiState(it) }
.map { Result.success(it) }
.startWith(Result.loading())
.onErrorReturn { handleError(it) }
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe({
outputState.postValue(it)
})
}
private fun handleError(error: Throwable): Result<UiState> {
return if (error is RetrofitException) {
when (error.kind) {
RetrofitException.Kind.NETWORK -> Result.failure(NetworkError(error))
RetrofitException.Kind.HTTP -> Result.failure(ServerError(error))
RetrofitException.Kind.UNEXPECTED -> Result.failure(UnknownError(error))
else -> Result.failure(UnknownError(error))
}
} else {
Result.failure(UnknownError(error))
}
}
class Factory #Inject constructor(private val someRepo: SomeRepository) : ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
#Suppress("UNCHECKED_CAST")
return SomeViewModel(someRepo) as T
}
}
}
As you can see here 2 streams: a uiEvents (1st stream) which gets all the input events from the UI. As long as the UI exists it will be catching those events. Based on the event types it calls some repository functions (use cases) that are returning some response and then they are updating the model (2nd stream) with one of the possible outcomes: Success, Error or Loading.
Also transform the errors in API to so called RetrofitErrors, and based on their type it can show different error messages to the User.
There is some duplication as well that can be avoided easily, but what I wanted to show here is that it always start with a Loading result, then either a Success or an Error.
One of the most important thing is that this way "To keep state in the stream, which is a LiveData."
One benefit of this setup (just like using a BehaviourSubject) is that it will always return the last state — on orientation change it is very useful as it just loads the last available state.
Also it is highly testable as each piece can be tested in separation with providing mocked repo or view and it is also very easy to debug as we always have a current state in the stream.

How can I wait for an object filled asynchronously in Android UI thread without blocking it?

I have a singleton to handle the registration and elimination of an entity Profilo ( a Profile).
This entity is set by passing an identifier and gathering information on the server in an async way.
My problem is that when I have to return my instance of profilo if it's not still loaded it will return null.
public class AccountHandler {
private static AccountHandler istanza = null;
Context context;
private boolean logged;
private Profilo profilo;
private AccountHandler(Context context) {
this.context = context;
//initialization
//setting logged properly
assignField(this.getName());
}
}
public static AccountHandler getAccountHandler(Context context) {
if (istanza == null) {
synchronized (AccountHandler.class) {
if (istanza == null) {
istanza = new AccountHandler(context);
}
}
}
return istanza;
}
public void setAccount(String nickname, String accessingCode) {
logged = true;
assignField(nickname);
}
//other methods
private void assignField(String nickname) {
ProfiloClient profiloClient = new ProfiloClient();
profiloClient.addParam(Profilo.FIELDS[0], nickname);
profiloClient.get(new JsonHttpResponseHandler() {
#Override
public void onSuccess(int statusCode,
Header[] headers,
JSONArray response) {
JSONObject objson = null;
try {
objson = (JSONObject) response.getJSONObject(0);
} catch (JSONException e) {
e.printStackTrace();
}
AccountHandler accountHandler = AccountHandler.getAccountHandler(context);
// Profilo is created with a JSONObject
// **setProfilo is called in async**
**accountHandler.setProfilo(new Profilo(objson));**
}
});
}
private void setProfilo(Profilo profilo) {
this.profilo = profilo;
}
public Profilo getProfilo() {
if( logged && profilo == null)
//How can I wait that profilo is loaded by the JsonHttpResponseHandler before to return it
return this.profilo;
}
}

Instead of calling getProfilo you could use a callback mechanism in which the AccountHandler class notifies the caller when the profile has been loaded. e.g.
public void setAccount(String nickname, String accessingCode, MyCallback cb) {
assignField(nickname, cb);
}
private void assignField(String nickname, MyCallback cb) {
....
accountHandler.setProfilo(new Profilo(objson));
cb.onSuccess(this.profilo);
}
Create an inner Interface MyCallback (rename it) in your AccountHandler class
public class AccountHandler {
public interface MyCallback {
void onSuccess(Profilo profile);
}
}
Now whenever you call setAccount you will pass the callback and get notified when the profile is available e.g.
accountHandler.setAccount("Test", "Test", new AccountHandler.MyCallback() {
void onSuccess(Profilio profile) {
// do something with the profile
}
}

I added, as #Murat K. suggested, an interface to my Class that will provide a method to be call with the object when it is ready to be used.
public class AccountHandler {
public interface Callback {
void profiloReady(Profilo profilo);
}
}
This method is called in getProfilo in a Handler that makes recursive calls to getProfilo until profilo is ready to be used, then it call the callback method which class is passed as argument of getProfilo.
public void getProfilo(final Callback Callback) {
if( logged && (profilo == null || !profilo.isReady() ) {
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
getProfilo(Callback);
}
}, 500);
}else
Callback.profiloReady(profilo);
}
Example of getProfilo call
public class ProfiloCall implements AccountHandler.MyCallback {
#Override
public void profiloReady(Profilo profilo) {
//Use profilo as needed
//EXECUTED ONLY WHEN PROFILO IS READY
}
public void callerMethod() {
//useful code
accountHandler.getProfilo(this);
//other useful code
}
}

Android notify() method is not called

I'm trying to use notify() and wait(). Here is my desired class.
I have a problem, when I try to call addNewItem(). If I call tryToReadItem() first and then call addNewItem() method, that log will not be printed. Note that my DemoClass is the singleton.
public class DemoClass {
private static final String TAG = "DemoClass";
private static DemoClass instance;
private Object lock = new Object();
private static Thread executor;
private static Runnable reader;
static MyQueue queue;
private DemoClass() {
queue = MyQueue.getInstance();
reader = new Runnable() {
#Override
public void run() {
tryToReadRequest();
}
};
}
public static DemoClass getInstance() {
if (null == instance) {
instance = new RequestExecutor();
executor = new Thread(reader);
executor.run();
}
return instance;
}
public boolean addNewItem() {
synchronized (lock) {
lock.notify(); // executor will be run
Log.i(TAG, "executor run...");
}
return true;
}
public void tryToReadItem() {
try {
while (true) {
synchronized (lock) {
if (queue.checkTopValue() == null) {
Log.v(TAG, "queue is empty");
lock.wait();
} else {
//TODO other code...
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
Here is the usage of that class:
DemoClass executor = DemoClass.getInstance();
boolean bool = executor.addNewItem();
Am I missing something?
Edit: I just changed my code. Now tryToReadRequest() is executed continuously while queue is not empty. but my problem is that the line lock.notify(); does not execute.

There are many problems with this code
First of all
if (queue.checkTopValue() == null) {
Log.v(TAG, "queue is empty");
lock.wait();
}
Depends on official documentation
Note: Always invoke wait inside a loop that tests for the condition
being waited for. Don't assume that the interrupt was for the
particular condition you were waiting for, or that the condition is
still true.
Your DemoClass is Singleton. But not thread safe Singleton
because multiple threads can pass null == instance condition at the same time
if (null == instance) {
instance = new RequestExecutor();
executor = new Thread(reader);
executor.run();
}
Right way is additional check in synchronized block and using volatile instance.
so add volatile to instance
private static volatile DemoClass instance;
and rewrite getInstance() method to something like this
public static DemoClass getInstance() {
DemoClass localInstance = instance;
if (localInstance == null) {
synchronized (DemoClass.class) {
localInstance = instance;
if (localInstance == null) {
localInstance = new DemoClass();
instance = localInstance;
executor = new Thread(reader);
executor.run();
}
}
}
return localInstance;
}
note, you can leave only check inside synchronized block, but that will make getInstance method too slow.

Why does my subscribe never complete?

I am trying to learn about rxJava and reactive programming in context of android and I feel I am nearly there, I just can't quite grasp the complete picture to fully understand what I am doing.
I have the below code which gets a list of instances of a class called iApps from the database
myHelper m = new myHelper(getApplication());
m.getApps()
.observeOn(Schedulers.newThread())
.subscribe(currentApps::addAll,
throwable -> Log.e("Error Observable", throwable.toString() + " " + Arrays.toString(throwable.getStackTrace())),
() -> compareLists(availableApps, currentApps));
}
Which uses the following methods:
//From my database caller function
public Callable<ArrayList<iApp>> getApps()
{
return this::getCurrentInfo;
}
A custom helper function
public class myHelper {
Context ctx;
tQuery t;
public myHelper(Context _ctx)
{
this.ctx = _ctx;
t = new tQuery(_ctx);
}
Observable<ArrayList<iApp>> getApps()
{
return makeObservable(t.getApps())
.subscribeOn(Schedulers.computation());
}
private static <T> Observable<T> makeObservable(final Callable<T> func) {
return Observable.create(
new Observable.OnSubscribe<T>() {
#Override
public void call(Subscriber<? super T> subscriber) {
try {
subscriber.onNext(func.call());
} catch (Exception ex) {
subscriber.onError(ex);
}
}
});
}
}
However my on complete never runs. I have checked the onNext by looping through the results of iApp and outputting one of the fields so I can see that the data is being collected, however my compareLists function is never run.
Could someone explain my oversight?

Well that was embarassing!
private static <T> Observable<T> makeObservable(final Callable<T> func) {
return Observable.create(
new Observable.OnSubscribe<T>() {
#Override
public void call(Subscriber<? super T> subscriber) {
try {
subscriber.onNext(func.call());
subscriber.onCompleted();
} catch (Exception ex) {
subscriber.onError(ex);
}
}
});
}

Custom Loader for endless scrolling

I'm trying to create a custom loader which loads an list of data that works fine but now I want to added endless scrolling in the listview. I thought a logical place would be in the loader since almost all the examples I see on the interwebz have a private field in the custom loader which corresponds with the data to be returned to UI and in the deliverResult there is some code like this
#Override
public void deliverResult(T data) {
T oldData = mData;
mData = data;
if (isStarted()) {
// If the loader is currently started, we can immediately deliver a result
super.deliverResult(mData);
}
}
No I thought that mData still contains the previous list [1,2,3,4,5] cause the loader should cache the data to show it instantaneously on configuration changes. And data is the new list [6,7,8,9,10] for instance. I could just add data to mData, mData.add(data) and we are done. Don't have to repeat the code on multiple places or different adapters. But seemingly this doesn't work, everytime you call restartLoader to load the new data the framework creates a new instance of the Loader. Has anyone else run into this problem before? or should I just do the mData.add(data) in the Adapter or somewhere else in the code.
the full implementation of the custom loader which extends ApiResponseLoader which can also be find below:
public class SearchLoader extends ApiResponseLoader {
private SearchType mSearchType;
private int mOffset;
private String mSearchQuery;
public SearchLoader(Context context, SearchType type, int offset, String query) {
super(context);
mSearchType = type;
mOffset = offset;
mSearchQuery = query;
}
#Override
public ApiResponse loadInBackground() {
try {
Map<String, String> parameters = Utils.parametersMap("q:" + mSearchQuery, "offset:" + String.valueOf(mOffset));
return tryLoadInBackground(parameters);
} catch (Exception e) {
setError(e);
return null;
}
}
public ApiResponse tryLoadInBackground(Map<String, String> parameters) throws Exception {
if (mSearchQuery == null) {
throw new NullPointerException("mSearchQuery should not be null");
}
if (mSearchType == SearchType.A) {
return RestAdapter().searchA(parameters);
} else {
return RestAdapter().searchB(parameters);
}
}
}
public abstract class ApiResponseLoader extends AsyncTaskLoader<ApiResponse> {
private final static String TAG = ApiResponseLoader.class.getSimpleName();
private ApiResponse mApiResponse;
private Exception mError;
public ApiResponseLoader(Context context) {
super(context);
}
public abstract ApiResponse tryLoadInBackground(Map<String, String> parameters) throws Exception;
#Override
protected void onStartLoading() {
if (mApiResponse != null) {
deliverResult(mApiResponse);
}
if (takeContentChanged() || mApiResponse == null) {
forceLoad();
}
}
#Override
protected void onForceLoad() {
super.onForceLoad();
}
#Override
protected void onStopLoading() {
cancelLoad();
}
#Override
public void onCanceled(ApiResponse data) {
// Attempt to cancel the current asynchronous load.
super.onCanceled(data);
}
#Override
protected void onReset() {
// Ensure the loader has been stopped.
onStopLoading();
// At this point we can release the resources associated with 'apps' if needed
if (mApiResponse != null) {
mApiResponse = null;
}
}
#Override
public void deliverResult(ApiResponse data) {
if (isReset()) {
// An async query came in while the loader is stopped. We don't need the result
if (data != null) {
onReleaseResources(data);
}
return;
}
if (mApiResponse != null) {
mApiResponse.mMeta = data.mMeta;
mApiResponse.mSampleList.addAll(data.mSampleList);
} else {
mApiResponse = data;
}
if (isStarted()) {
// If the loader is currently started, we can immediately deliver a result
super.deliverResult(mApiResponse);
}
}
public Exception getError() {
return mError;
}
public void setError(Exception mError) {
this.mError = mError;
}
}

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.

RxJava unsubscribeOn with recursive call not in the right thread - android

Related

How to Manage State with RxJava in Android using Java (Not Kotlin)

How can I wait for an object filled asynchronously in Android UI thread without blocking it?

Android notify() method is not called

Why does my subscribe never complete?

Custom Loader for endless scrolling

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