Extending Fragment: MainActivity is not an enclosing class when adding JavacriptInterface

I got the error MainActivity is not an enclosing class when I try to addJavascriptInterface to the Webview inside the extended Fragment class:

mXWalkView.addJavascriptInterface(new MainActivity.JS_Bind(this, mXWalkView),"Android");

In my MainActivity I implented it this way in the onCreate method:

mXWalkView.addJavascriptInterface(new JS_Bind(this, mXWalkView),"Android");

And JS_Bind is a public class inside MainActivity:

public class JS_Bind {
    private static final String TAG = "JS_Bind";
    private Context context;
    private XWalkView mXWalkView;

    public JS_Bind(Context c, XWalkView mXWalkView) {
        context = c;
        this.mXWalkView = mXWalkView;
    }

    @org.xwalk.core.JavascriptInterface
    public void makeToast(String toast) {
        Toast mToast = Toast.makeText(context, toast, Toast.LENGTH_SHORT);
        mToast.setGravity(Gravity.CENTER, 0, 0);
        mToast.show();
    }
}

Note: I also use Crosswalk (a Webview library). How can I fix this error and what exactly does it mean? I read similiar questions and answers but didn't understand it.

Edit: Fragment class:

public class SlideFragment extends Fragment {
    private XWalkView mXWalkView;
    private Context c;

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_demo, container, false);

    }

   @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        int position = FragmentPagerItem.getPosition(getArguments());

        XWalkPreferences.setValue(XWalkPreferences.REMOTE_DEBUGGING, true);
        mXWalkView.addJavascriptInterface(new MainActivity.JS_Bind(this, mXWalkView),"Android");
        mXWalkView = (XWalkView) view.findViewById (R.id.webView);
        mXWalkView.clearCache(true);

        mXWalkView.load(MainActivity.ROOT + "?s=" + getArguments().getString("title") + ".php?page=" + position, null);