Update Spinner items at runtime

Question

I have a spinner that returns the saved cities in my comic book, when this city does not exist, I allow to register the same, and after registering and saving, I make to close the city registration Activity and return to the previous one that would be Activity containing the spinner, Only this city that just got saved doesn’t show up on my spinner, I have to get out of the app and back in it again so I can update that information. How do I update the spinner data at runtime, that is how I return to Activity that contains the spinner? Follow in my spinner:

List<String> labels = ds.getAllLabels();

spin = (Spinner) findViewById(R.id.spinner);

ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
    android.R.layout.simple_spinner_item,labels);

dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spin.setAdapter(dataAdapter);