Problem description

I writing an Android application in Java to handle RFID reading based on some proprietary library and hardware. The RFID reader has a JNI library, which acts as an API to the hardware. This library is thread safe (as they say) but I cannot make the scanning process run on the Android's UI thread. I also don't want to use AsyncTask because it has started being deprecated I want the user to be able to start/resume the scanning process based on the click of a button without the process starting each time from the beginning.

I have the following code inside a class Scanner that is a singleton object.

class Scanner {
/*...*/
    public Observable<Product> scan() {
        return Observable.create(emitter -> {
            while (true) {
                 UHFTAGInfo TAG = RFIDReader.inventorySingleTag();
                 if (TAG != null) {
                    emitter.onNext(new Product(TAG.getEPC()));
                 }
            }
        });
    }
/*...*/
}

On the UI side, I have a ScanFragment and some buttons. This is the OnClickListener() of the scanButton that triggers the scanning process.

scanButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
         Scanner.getInstance().scan()
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Observer<Product>() {
                @Override
                public void onSubscribe(@NonNull Disposable d) {

                }

                @Override
                public void onNext(@NonNull Product product) {
                    listProducts.add(product);
                    adapter.notifyDataSetChanged();
                }

                @Override
                public void one rror(@NonNull Throwable e) {

                }

                @Override
                public void onComplete() {

                }
            });
}

Questions

• What is the correct way to stop/resume/end the above infinite emitting Observable when another stopButton/resumeButton is pressed or when user moves to another fragment?
• I have thought many different things like an Atomic flag without and with an Observable for it and using takeUntil for that Observable. But will takeUntil stop my Observable and I will have to start it from the beginning?

CodePudding user response：

First of all, you have an unconditional infinite loop which is unable to respond to when the downstream disposes the sequence. Use while (!emitter.isDisposed()).

Stopping a sequence is done via Disposable.dispose. You get one Disposable in onSubscribe so you'll have to make that available to the button that you want to stop a sequence.

Resuming is essentially subscribing to the sequence again, i.e., what you already do in that onClick callback.