Conditional and Parameterised transitions

[Brett Bailey]

Is it possible to access the parameter of a parameterised transition in the guard clause of  PermitIf().

For example I would like to do something like this:

_assignTrigger = _machine.SetTriggerParameters<string>(Trigger.Assign);

_machine.Configure(State.Assigned)

.PermitIf(_assignTrigger, OrderState.Blocked, x => IsBlackListed(x))

.Permit(_assignTrigger, OrderState.Accepted)

_machine.Fire(_assignTrigger, "j...@example.com") //transition to Accepted unless email is blacklisted

Cheers

~Brett

[Simon]

I've tried that as well but no luck, I think you can only us the parameter in the OnEntry(). 

Would be a good addition to the framework though!

[Grant BlahaErath]

Yes.  PermitDynamic(aTrigger, (aParam) => { .... });  should do the trick.  You have to resolve the state for that trigger in that lambda function, rather than let it iterate through a cluster of PermitIf conditionals.    I also recommend throwing an exception (like InvalidOperation) if there is no match or obvious fall through condition since that means your automaton is incomplete.

 

You can think of PermitIf as a subset of PermitDynamic.  PermitIf is a collection of conditional statements that is iterated over, while PermitDynamic performs the same role without the iteration of a collection.  Inside the PermitDynamic would be one or more if/then/return state statements.  Or, if the conditionals are too complex, create a second state machine inside the PermitDynamic.  I like using PermitDynamic for resolving WPF RoutedCommands.

 

-g