[Qt-interest] Using QStateMachine in large apps (Was qscxml and Qhttp)

[Stephen Kelly]

noam.rosenthal at nokia.com wrote:

> Actually, the problem is the build order
> You have to make install scc before you can compile the examples under
> examples/scc. That's because the stuff under examples/scc requires scc.prf
> to be installed in [QTDIR]/mkspecs/features.
> 
> So:
> 
> cd scc
> [QTDIR]/bin/qmake
> make install
> 
> cd ..
> make

Thanks for that. I managed to build the module and build and try the 
examples. They seem to work well. I tried make docs, but that didn't work, 
so I tried cd doc && qdoc scxml.qocconf, which also did nothing useful (I 
don't really know how to use qdoc), so I just read the doc source.

I'm new to QStateMachine and am planning to use it in kontact-mobile and 
another large project. I just read through the docs a couple of days ago. I 
was wondering if there was a better way to maintain the state machine than 
in C++ code. I thought at first that qscxml would be the answer, and it 
might be. Maybe you can clarify. It seems to aimed towards implementing the 
state machine in xml+QtScript. 

My aim is to implement my own transition class so that I can change states 
based on selections in a QItemSelectionModel. Such a thing would be defined 
in a header file which could be specified in a similar way to how they are 
specified in .ui files.

Given that, I'd do something like this (and I know it's not valid scxml :)):

<statemachine>
  <state id="no selection" 
         object="myObject" 
         property="something" 
         value="9" />
  <state id="single selection" 
         object="myObject" 
         property="something" 
         value="42" />
  <transition type="ModelSelectionTransition" 
              definition="modelselectiontranstion.h"
              from="no selection"
              to="single selection">
    <property name="mode" value="SingleSel" /> 
  </transition>
</statemachine>

the ModelSelectionTransition class would set up the connection to the 
selectionChanged signal and would implement the logic of whether to run the 
transition for a particular value in the selectionChanged.

So the above would generate code something like this:

QObject *myObject = getSomeObject();
myObject->setObjectName("myObject");

QStateMachine machine;
QState *noSel = new QState();
noSel->assignProperty(myObject, "something", 9);
QState *singleSel = new QState();
singleSel->assignProperty(myObject, "something", 42);

ModelSelectionTransition *tr = new ModelSelectionTransition(SingleSel);
tr->setTargetState(singleSel);
noSel->addTransition(tr);

where ModelSelectionTransition is something like

class ModelSelectionTransition 
{

  bool eventTest(QEvent *e)
  {
    if (m_type == SingleSel)
      // if the selection model has only one item, accept it.
    if (m_type == MultiSel)
      // ...
  }

};

The engine for the scxml description would need to have a Context to inject 
the myObject into it etc. It looks like QScxml::registerObject does exactly 
that. What is the RightWay to use qscxml to what I'm trying to achieve?

Sorry for the brain-dump post. I haven't written any code for this yet, only 
read documentation so far. Hope I got it right.

All the best,

Steve.