title: Two successive BLOCs in flutter_bloc
body: <p>I want to split my BLOC into two BLOCs:</p>
  <ol>
  <li>the one who does preparing job</li>
  <li>the main one</li>
  </ol>
  <p>Let's call it PrepBloc and MainBloc. Is it reasonable way to put one inside another like this:</p>
  <pre><code>BlocProvider&lt;PrepBloc&gt;(
            create: ......,
            child: AppView()
          )
  class AppView extends StatelessWidget {
    Widget build(BuildContext context) {
      return BlocBuilder&lt;PrepBloc, PrepState&gt;(
        builder: (context, state) {
          if (state is ReadyState) {
            return BlocProvider&lt;MainBloc&gt;(...);
          }
          else if (state is NotReadyState) {
            return PrepPage();
          }
        }
      );
    }
  }
  </code></pre>
  <p>I know there is MultiBloc thing but it seems to me a little sophisticated and producing a lots of code.</p>