Fill spinner with array of strings returned from Javascript function in Fragment layout

I'm trying to fill a spinner in a fragment layout with an array of strings that I get returned from a Javascript function of my WebView page.

This is my scenario: I'm in fragment1 which has a webview1. I click on something in the webview1 and I go to fragment2 which has another WebView2. I want to fill a spinner in fragment2 with an array returned from a function wrote in the page that is being loaded in WebView2.

js function wrote in the page that is gonna load in WebView2:

function test(){
    var cars = ["Saab", "Volvo", "BMW"];
    window.JSInterface.callback(cars);
}

And this is my fragment2 code:

public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    view = inflater.inflate(R.layout.fragment_edificio, container, false);

    ...

    wv.getSettings().setJavaScriptEnabled(true);
    Fragment2.JavaScriptInterface jsInterface = new 
                   Fragment2.JavaScriptInterface(getActivity());
    wv.addJavascriptInterface(jsInterface, "JSInterface");
    wv.loadUrl("file:///android_asset/"+idEdificio+"-p0.html"); // point it to the SVG
    wv.setBackgroundColor(0x00000000);

    wv.setWebChromeClient(new WebChromeClient() {

        public void onProgressChanged(WebView view, int progress) {
            progressBar.setProgress(progress);
            if(progress == 100) {
                //wait for page to load

                wv.loadUrl("javascript:test()");                   
            }
        }
    });


    return view;
}

And this is my JSInterface for callbacks from WebView page

public class JavaScriptInterface {
    private Activity activity;

    public JavaScriptInterface(Activity activity) {
        this.activity = activity;
    }

    @JavascriptInterface
    public void loadEdificio(){

        loadFragment(new FragmentEdificio());
    }
    @JavascriptInterface
    public void callback(String[] value) {
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                getActivity(), android.R.layout.simple_spinner_item, value);

        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setAdapter(adapter);
    }
}

What happens is that i get the array returned but the spinner doesn't fill up, but if put these lines in the OnCreateView() the spinner does fill up :

String[] value = {"value1", "value2"};
ArrayAdapter<String> adapter = new ArrayAdapter<String>(
            getActivity(), android.R.layout.simple_spinner_item, value);

adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);;

From what I undertood is that the callbacks from the webview are handled in a different thread and what I'm trying to do cannot be done. Is there a different way to do this? Or am I missing something?

Thanks in advance!