back.java

if (getDialog() != null) {
 getDialog().setOnKeyListener(new OnKeyListener() {
    @Override
    public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) {
       if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_UP) {
          onBackPressed();
       }
       return true;
    }
 });
}