Scanning barcode method doesn't work after back is pressed

Question

I'm developing one app on CIPHERLAB device that has two lateral physical buttons that activate the laser and can scar some barcodes.

My main issue is all what i would make it do works properly but if i get back to another activity by pressing back button and return to the same activity where i can scan the barcode the app crash if i scan another code and when i return to that activity it gives following errors and crash if i scan a code:

06-11 12:11:47.211 25170-25170/com.example.igardini.visualposmobile E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.igardini.visualposmobile, PID: 25170 android.view.WindowManager$BadTokenException: Unable to add window -- token android.os.BinderProxy@89ed74e is not valid; is your activity running? at android.view.ViewRootImpl.setView(ViewRootImpl.java:796) at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:351) at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:93) at android.app.Dialog.show(Dialog.java:322) at com.example.igardini.visualposmobile.cassa.CustomAllert(cassa.java:217) at com.example.igardini.visualposmobile.cassa$2.run(cassa.java:123) at android.os.Handler.handleCallback(Handler.java:836) at android.os.Handler.dispatchMessage(Handler.java:103) at android.os.Looper.loop(Looper.java:203) at android.app.ActivityThread.main(ActivityThread.java:6251) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)

Here is my cassa.java activity code where i've implemented method which i use to scan the barcode with the laser and print it as a String.

     @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_cassa);

    editText = findViewById(R.id.editTextBar);

    myDB = new DataBaseHandler(this);

    itemCassas = new ArrayList<>();
    buildTopRecyclerView();

     loadData();
     buildRecyclerView();


    price = findViewById(R.id.priceText);


    m_RM = ReaderManager.InitInstance(getApplicationContext());
    mReaderCallback = cassa.this;

    IntentFilter filter = new IntentFilter();
    filter.addAction(GeneralString.Intent_READERSERVICE_CONNECTED);
    registerReceiver(myDataReceiver, filter);


}


@Override
protected void onDestroy() {
    super.onDestroy();
    unregisterReceiver(myDataReceiver);
}

private final BroadcastReceiver myDataReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        if (intent.getAction().equals(GeneralString.Intent_READERSERVICE_CONNECTED)) {

            if(mReaderCallback != null){
                m_RM.SetReaderCallback(mReaderCallback);
            }

        }
    }
};



// getting a string of barcode after scanning it

@Override
public void onDecodeComplete(final String arg0) throws RemoteException {
    this.runOnUiThread(new Runnable() {
        @Override
        public void run() {
            editText.setText(arg0);

            // using the string got from the scanning for searching some data from the DB

            if(!TextUtils.isEmpty(editText.getText().toString())) {
                searchKeyword = editText.getText().toString();
                result = myDB.dbRawSearch(searchKeyword);

                if(result != null) {
                    String[] split = result.split("\n");

                    if (!split[0].equals("")) {
                        resultArt = myDB.dbRawArticoli(split[0]);

                        String[] splitArt = resultArt.split("\n");

                        itemCassas.add(new ItemCassa(splitArt[0], splitArt[1], Double.parseDouble(splitArt[2].replace(",", "."))));
                        exampleAdapter.notifyItemInserted(itemCassas.size());
                    } else {
                        CustomAllert();
                    }
                }
            }
        }
    });
}

@Override
public IBinder asBinder() {
    return null;
}


// Funzione per il controllo del pulsante Back
@Override
public void onBackPressed() {
    overridePendingTransition(android.R.anim.fade_in, android.R.anim.fade_out);
    super.onBackPressed();

}

public void CustomAllert(){
    AlertDialog.Builder mBuilder = new AlertDialog.Builder(this);

    @SuppressLint("InflateParams") View mView = getLayoutInflater().inflate(R.layout.alert_dialog, null);

    Button button = mView.findViewById(R.id.btnOK);

    mBuilder.setView(mView);
    final AlertDialog dialog = mBuilder.create();
    dialog.show();
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            dialog.dismiss();

        }
    });


}