How can I restart BarcodeDetector for new result when I return to the activity?

Question

I have a QR scanner activity which moves to the next activity on successful code scan. However, I want to have a back button to return to the activity (if this result may be incorrect). When I return to the activity, however, the result is still stored and the scanner is not scanning for codes.

How can I restart the barcode detector? Should I override onPause/onResume? Below is my code thus far.

private void setupBarcodeDetector() {

        barcodeDetector =
                new BarcodeDetector.Builder(this).setBarcodeFormats(Barcode.QR_CODE).build();
        cameraSource =

new CameraSource.Builder(this, barcodeDetector)
                        .setRequestedPreviewSize(640, 480)
                        .build();

        surfaceView
                .getHolder()
                .addCallback(
                        new SurfaceHolder.Callback() {
                            @Override
                            public void surfaceCreated(SurfaceHolder holder) {
                                if (ActivityCompat.checkSelfPermission(
                                                getApplicationContext(), Manifest.permission.CAMERA)
                                        != PackageManager.PERMISSION_GRANTED) {
                                    return;
                                }
                                try {
                                    cameraSource.start(holder);
                                } catch (IOException e) {
                                    e.printStackTrace();
                                }
                            }

                            @Override
                            public void surfaceChanged(
                                    SurfaceHolder holder, int format, int width, int height) {
                                // LEAVE EMPTY
                            }

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

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

                    @Override
                    public void receiveDetections(Detector.Detections<Barcode> detections) {
                        final SparseArray<Barcode> qrCodes = detections.getDetectedItems();

                        if (qrCodes.size() != 0) {
                            barcodeDetector.release();
                            resultQRtv.post(
                                    new Runnable() {
                                        @Override
                                        public void run() {
                                            Vibrator vibrator =
                                                    (Vibrator)
                                                            getApplicationContext()
                                                                    .getSystemService(
                                                                            Context
                                                                                    .VIBRATOR_SERVICE);
                                            vibrator.vibrate(500);
                                            successPrompt.setVisibility(View.VISIBLE);
                                            allGoodTv.setVisibility(View.VISIBLE);

                                            // Loading animation - to be changed with specific
                                            // animation
                                            if (dialog == null) {
                                                dialog =
                                                        new ProgressDialog(
                                                                QRCodeScannerActivity.this);
                                                dialog.setCancelable(false);
                                                dialog.setMessage("Registering...");
                                            }

                                            dialog.show();

                                            Handler handler = new Handler();
                                            handler.postDelayed(
                                                    new Runnable() {
                                                        @Override
                                                        public void run() {
                                                            // On successful scan, go to the required
                                                            // activity
                                                            Intent
                                                                    goToAdminAccountConfirmationActivity =
                                                                            new Intent(
                                                                                    QRCodeScannerActivity
                                                                                            .this,
                                                                                    AdminAccountConfirmSettings
                                                                                            .class);
                                                            startActivity(
                                                                    goToAdminAccountConfirmationActivity);

                                                            // Remove the prompts in case the user
                                                            // returns to this activity
                                                            dialog.dismiss();
                                                            successPrompt.setVisibility(View.GONE);
                                                            allGoodTv.setVisibility(View.GONE);

                                                        }
                                                    },
                                                    1500);
                                        }
                                    });
                        }
                    }
                });
    } // setupBarcodeDetector

Answer 1

In your case call setupBarcodeDetector() method inside onResume() method of your activty. for batter optimisation do the initialization in onCreate() method and start and stop scanning inside onPause() and onResume() methods.