Java map.putString not working within listener

Question

I am working on a program in Java that is reading QR codes from images. I have the following code:

@Override
    public Object callback(ImageProxy imageProxy, Object[] params) {
        WritableNativeMap writableNativeMap = new WritableNativeMap();

        BarcodeScannerOptions options =
                new BarcodeScannerOptions.Builder()
                        .setBarcodeFormats(Barcode.FORMAT_QR_CODE)
                        .build();

        Image mediaImage = imageProxy.getImage();

        final List<Barcode>[] barcodesList = new List[]{Collections.<Barcode>emptyList()};

        if (mediaImage != null) {
            InputImage image =
                    InputImage.fromMediaImage(mediaImage, imageProxy.getImageInfo().getRotationDegrees());

            BarcodeScanner scanner = BarcodeScanning.getClient(options);

            Task < List < Barcode >> result = scanner.process(image);

            result.addOnSuccessListener(new OnSuccessListener < List < Barcode >> () {
                @Override
                public void onSuccess(List < Barcode > barcodes) {
                    for (Barcode barcode: barcodes) {
                        int valueType = barcode.getValueType();

                        switch (valueType) {
                            case Barcode.TYPE_TEXT:
                                // TODO
                            case Barcode.TYPE_URL:
                                Log.d(TAG, barcode.getUrl().getUrl());
                                writableNativeMap.putString("URL", barcode.getUrl().getUrl());
                                // TODO
                                break;
                        }
                    }
                }
            }).addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    // ...
                }
            })
            .addOnCompleteListener(results -> imageProxy.close());
        }

        return writableNativeMap;
    }

When I call this function it will return {}. Even when it reached the Log.d statement in the Barcode.TYPE_URL case. So I know that it is putting stuff in the writableNativeMap. When I do a .putString just before the return statement then it works. Can someone help me with this?

Answer 1

Okay so to solve the problem I used a notifier as following:

    @Override
    public Object callback(ImageProxy imageProxy, Object[] params) {
        // Added this
        final AtomicReference<WritableNativeMap> notifier = new AtomicReference();

        WritableNativeMap writableNativeMap = new WritableNativeMap();

        BarcodeScannerOptions options =
                new BarcodeScannerOptions.Builder()
                        .setBarcodeFormats(Barcode.FORMAT_QR_CODE)
                        .build();

        Image mediaImage = imageProxy.getImage();

        final List<Barcode>[] barcodesList = new List[]{Collections.<Barcode>emptyList()};

        if (mediaImage != null) {
            InputImage image =
                    InputImage.fromMediaImage(mediaImage, imageProxy.getImageInfo().getRotationDegrees());

            BarcodeScanner scanner = BarcodeScanning.getClient(options);

            Task < List < Barcode >> result = scanner.process(image);

            result.addOnSuccessListener(new OnSuccessListener < List < Barcode >> () {
                @Override
                public void onSuccess(List < Barcode > barcodes) {
                    if (barcodes.size() > 0){
                        Barcode barcode = barcodes.get(0);

                        int valueType = barcode.getValueType();

                        switch (valueType) {
                            case Barcode.TYPE_TEXT:
                                writableNativeMap.putString("type", "TEXT");
                                writableNativeMap.putString("value", barcode.getRawValue());
                                break;
                            case Barcode.TYPE_URL:
                                writableNativeMap.putString("type", "URL");
                                writableNativeMap.putString("value", barcode.getUrl().getUrl());
                                break;
                            default:
                                writableNativeMap.putString("type", "OTHER");
                                writableNativeMap.putString("value", barcode.getRawValue());
                        }
                    }

                    // Added this
                    synchronized (notifier) {
                        notifier.set(writableNativeMap);
                        notifier.notify();
                    }
                }
            }).addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    // Added this
                    synchronized (notifier) {
                        notifier.set(writableNativeMap);
                        notifier.notify();
                    }
                }
            })
            .addOnCompleteListener(results -> imageProxy.close());
        }

        // Added this
        synchronized (notifier) {
            while (notifier.get() == null) {
                try {
                    notifier.wait();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        }

        return notifier.get();
    }