class BaseFragment() {
   private val viewHandler = Handler(Looper.getMainLooper())

   protected fun postViewAction(action: () -> Unit) {
        viewHandler.post(action)
   }
}

class ShowcaseFragment : BaseFragment() {
   override fun showRefreshProgress(visible: Boolean) {
        postViewAction {
            showcaseRefreshLayout?.isRefreshing = visible
        }
   }
}