[Qt-interest] Is it possible with the State Machine Framework?

[Sean Harmer]

Hi,

On Thursday 15 April 2010 09:13:13 Mihail Naydenov wrote:
> Hi, thank You, for your interest.
> 
> Right now the (easy) way to do work in states is to make some state
> automatically assign properties of some object (on state change).
> 
> state->assignProperty(object, property, value)
> 
> Now the object has defined meaning what is like to be in that state.
> You don't have to manually mange the object yourself, now it is smart and
> reacts automatically to the events that alter the sate. This is very
> powerful, because in a way a state represents an environment for the
> object: Here is an object, you set this and that directly, and the rest is
> handled behind the scenes, based on some external factors not of interest
> to the user.
> 
> For instance: You have a control (an icon) when clicked it does a work. You
> have a drawer/ tool window. The drawer can be "open" and "closed". Now,
> you can drag the icon in and outside the drawer in a way changing its
> environment. When in the drawer - it also "opens" and "closes", if not in
> - its always "open" (which might or might not affect what it does).
> The drawer open/close can be managed by a state - one for "open", one fore
> "closed". This state will do all the work - it will set all the props all
> over the drawer window and its contents. Lets say it hides all on close.
> The beauty is - every control can define what it is to be in that sate.
> Our icon for instance, when dragged into the drawer will also become part
> of the drawer's state, but might be made semi transparent instead of just
> hidden, by "attaching" the right property to the sate
> (drawer_open->assignProperty(icon, "opacity", 1) ; 
> drawer_closed->assignProperty(icon, "opacity", 0.5)).
> 
> So far so good, problem is if we want our icon out of the drawer again,
> there is no way to break the link with the drawer state. Outside of the
> drawer it will still go semi transparent when the drawer is opened closed.
> What we want is, upon dragging out, to "detach" or "unassing" the opacity
> and to manually set it to 1 (or let some other state handle it)
> 
> Again, I might be missing something.
> I know it possible to implement this with custom state and or custom
> transition or destroy and recreate the states every time... but then
> again, its also possible to implement it without states at all :)

I'm not entirely sure that I follow all of your example but it seems to me 
that you simply need to introduce a new pair of states that sets the property 
of your icon independently to the state of your tool window. I think you 
problem stems from trying to control orthogonal properties on two object using 
the same pair of states.

So I think you need to have four states in your case:

* drawer_open
* drawer_closed
* icon_in_drawer (set opacity to 0.5)
* icon_not_in_drawer (set opacity to 1)

I would try to arrange these in your state machine as two pairs of parallel 
sub-states since the state of the drawer is independent of the state of the 
icon. You can still get a degree of interaction between them by usign guarded 
transitions. If I have misunderstood your problem then you may need to have a 
different arrangement of states.

If you emit a signal when the icon is moved in or out of the drawer you can 
simply use QSignalTransitions to transition between the icon states.

HTH,

Sean