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i am programming an App with some Android Scanners to scan a few barcodes and put them into a list. If you scan a code, which is already in the list, a toast shall appear on the screen. The problem is it doesn't.

This is the method which is called after a scan (it is located in the MainActivity):

public void onData(ScanDataCollection scanDataCollection) {
    // The ScanDataCollection object gives scanning result and the collection of ScanData
    // Check the data and its status.
    String dataStr = "";
    if ((scanDataCollection != null) && (scanDataCollection.getResult() == ScannerResults.SUCCESS)) {
        ArrayList<ScanDataCollection.ScanData> scanData = scanDataCollection.getScanData();
        for (ScanDataCollection.ScanData data : scanData) {
            // Get the scanned dataString barcodeData
            String barcodeData = data.getData();
            // Get the type of label being scanned
            ScanDataCollection.LabelType labelType = data.getLabelType();
            dataStr = barcodeData;
        }

        // Result of scanned data
        Log.i("SCANNER", "Scanned barcode " + dataStr);
        for (Container c : containerList) {
            if (c.getId().equals(dataStr)) {
                //Toast.makeText(this, "Container bereits vorhanden!", Toast.LENGTH_LONG).show();
                showToast("Container bereits vorhanden!");
                return;
            }
        }
        addNewContainer(dataStr);
    }
}

The called showToast() method:

public void showToast(String toast) {
    if (fragManager.findFragmentById(R.id.fragment_holder).getTag().equals("LIST_FRAGMENT")) {
        ((ListFragment) fragManager.findFragmentById(R.id.fragment_holder)).showToast(toast);
    }
}

And the showToast() method of the fragment:

public void showToast(String toast) {
    Log.i("FRAGMENT", "Before Toast");
    Toast.makeText(ctx, "Schon vorhanden!", Toast.LENGTH_LONG).show();
    Log.i("FRAGMENT", "After Toast");
}

The code does reach the toast, but it doesn't get any further. Log looks like this:

2020-12-03 16:49:00.422 6915-7014/com.fmg.containerapp I/SCANNER: Scanning...

2020-12-03 16:49:00.492 6915-7015/com.fmg.containerapp I/SCANNER: Scanned barcode AYYC411FX

2020-12-03 16:49:00.492 6915-7015/com.fmg.containerapp I/FRAGMENT: Before Toast

2020-12-03 16:49:00.507 6915-7016/com.fmg.containerapp I/SCANNER: Scanner is enabled and idle...

2020-12-03 16:49:00.552 6915-7017/com.fmg.containerapp I/SCANNER: Waiting for scan...

What did i do wrong, that the toast doesn't show up? I tried different contexts and it does work in the onCreateView() of every Fragment.

Thanks for your help

Skrootie
  • 1
  • The `onData()` method possibly runs on a separate worker thread, and you can only show `Toast`s from the main UI thread. There should be something in the logs about it, but either way you could test it in code pretty quickly: https://stackoverflow.com/a/9815528. – Mike M. Oct 29 '21 at 12:56

0 Answers0