[Boost-users] Re: boost::fsm, parameters to DestinationState

From: Andreas Huber (ahd6974-spamgroupstrap_at_[hidden])
Date: 2005-03-11 08:52:27

Jan Eickmann <je <at> framesys.de> writes:
> I'll try to give some more information. In the application we are 
> developing, we have a screen that is kind of like an encyclopedia. This 
> screen is usually shown after the user presses a "more information" 
> button in a popup dialog, etc.
> That encyclopedia-screen is the state I want to transit to. Now what I 
> want to do is tell that screen what entry to show.
> In order to be able to get back to the original state, I put the 
> "normal" GUI of the application in a state that has a deep-history.
> 
> So the common outer state would basicly be the FSM but I would rather 
> avoid having a variable there as this would require changing the FSM 
> itself everytime I want to add a similar screen that gets told from the 
> outside what to do exactly.

Hmmm, I not sure whether I already have enough information to help but you 
might consider posting an event containing the necessary information before 
making the transition. Of course, this does not help you accessing the 
information from the ctor of the state but the reaction that follows can then 
access this info, as follows:

// untested
struct EvButtonClicked : fsm::event< EvButtonClicked > {};

struct EvEntryInfo : fsm::event< EvEntryInfo >
{
  // Whatever you need to send goes here
};

struct Init;
struct Application : fsm::state_machine< Application, Init > {};

struct ShowEntry : fsm::simple_state< ShowEntry, Application >
{
  fsm::result react( const EvEntryInfo & info )
  {
    /* display info here */
  }
};

struct Init : fsm::simple_state< Init, Application,
  fsm::custom_reaction< EvButtonClicked > >
{
  fsm::result react( const EvButtonClicked & )
  {
    post_event( boost::intrusive_ptr( new EvEntryInfo() ) );
    return transit< ShowEntry >();
  }
};

I assume that you have a good reason not to use a GUI framework, which I 
expect to be better suited to implement the functionality you need than a 
general FSM framework.

HTH & Regards,

Andreas