Detector processor must first be set with setProcessor in order to receive detection results

Question

I am using Mobile Vision API to scan QR code.

I have this method in the activity to use the camera to capture the code:

private void createCameraSource() {
    final BarcodeDetector barcodeDetector = new BarcodeDetector.Builder(this).build();
    if(!barcodeDetector.isOperational()){
        Toast.makeText(this,
                "No se puede utilizar el detector de códigos de barra", Toast.LENGTH_LONG).show();
        this.finish();
    }
    else {
        final CameraSource cameraSource = new CameraSource.Builder(this, barcodeDetector)
                .setAutoFocusEnabled(true)
                .setRequestedPreviewSize(1600, 1024)
                .build();
        cameraPreview.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder surfaceHolder) {
                if (ActivityCompat.checkSelfPermission(RegisterActivity.this, Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED) {
                    try {
                        cameraSource.start(cameraPreview.getHolder());
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

            @Override
            public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {

            }

            @Override
            public void surfaceDestroyed(SurfaceHolder surfaceHolder) {
                cameraSource.stop();
            }
        });

        barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {
            @Override
            public void release() {

            }

            @Override
            public void receiveDetections(Detector.Detections<Barcode> detections) {
                final SparseArray<Barcode> barcodes = detections.getDetectedItems();
                if (!RegisterActivity.this.isProcessing() && barcodes.size() > 0) {
                    barcodeDetector.release();
                    RegisterActivity.this.setProcessing(true);
                    Intent intent = new Intent(RegisterActivity.this, ResultActivity.class);
                    intent.putExtra("code", codigo);
                    intent.putExtra("data", barcodes.valueAt(0));
                    setResult(CommonStatusCodes.SUCCESS, intent);
                    startActivity(intent);
                    RegisterActivity.this.setProcessing(false);
                    finish();
                }

            }
        });
    }
}

When a code is detected and read, I need to pass that code to other activity. That's why I have this code:

                if (!RegisterActivity.this.isProcessing() && barcodes.size() > 0) {
                    barcodeDetector.release();
                    RegisterActivity.this.setProcessing(true);
                    Intent intent = new Intent(RegisterActivity.this, ResultActivity.class);
                    intent.putExtra("code", codigo);
                    intent.putExtra("data", barcodes.valueAt(0));
                    setResult(CommonStatusCodes.SUCCESS, intent);
                    startActivity(intent);
                    RegisterActivity.this.setProcessing(false);
                    finish();
                }

When I run the application, this exception is shown in the logcat:

2020-08-27 18:19:53.894 11076-11746/com.company.myapp E/CameraSource: Exception thrown from receiver.
    java.lang.IllegalStateException: Detector processor must first be set with setProcessor in order to receive detection results.
        at com.google.android.gms.vision.Detector.receiveFrame(com.google.android.gms:play-services-vision-common@@19.1.2:17)
        at com.google.android.gms.vision.CameraSource$zza.run(com.google.android.gms:play-services-vision-common@@19.1.2:47)
        at java.lang.Thread.run(Thread.java:929)
2020-08-27 18:19:53.956 11076-11746/com.company.myapp E/CameraSource: Exception thrown from receiver.
    java.lang.IllegalStateException: Detector processor must first be set with setProcessor in order to receive detection results.
        at com.google.android.gms.vision.Detector.receiveFrame(com.google.android.gms:play-services-vision-common@@19.1.2:17)
        at com.google.android.gms.vision.CameraSource$zza.run(com.google.android.gms:play-services-vision-common@@19.1.2:47)
        at java.lang.Thread.run(Thread.java:929)

The application works because the new activity is opened and I can receive the read code there, but, if I set a breakpoint in that activity and start debugging, debugger session ends with no more errors after a few seconds.

What's wrong with that code?

Answer 1

Debugging sometimes changes the behavior of your code. Especially when your framework works with a lot of threads like android.

From the stacktrace at java.lang.Thread.run(Thread.java:929) I would say, that some code, in a thread, which is currently not under debugging wants to use the Decoder, before your call of setProcessor.

In Java only the thread which is under debugging will stop at a breakpoint other threads are not touched and won't be stopped when a breakpoint is reached.