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Recording and Mapping State Changes
This topic discusses how to set constraints against each State in the StateMachine under a Class, to define the change in state to be recorded.
Example
This example of a 'State Properties' dialog is for the State called Parliament; the 'Constraints' tab is open to show how the State is linked to the Class CXTrain.
A State can be defined by a single constraint or by many; in the example, the State Parliament has two constraints:
The values of constraints can only be compared for elemental, enum and string types
The CXTrain Class has a member called Location of type int, and a member called Departing.Name of type CString; what this constraint means is that this State is evaluated to True when:
- an instance of the CXTrain Class exists and
- its member variable Location has the value 0 and
the member variable Departing.Name has the value Parliament
Operators in Constraints
There are two types of operators you can use on constraints to define a State:
- Logical operators AND and OR can be used to combine constraints
- Equivalence operators {= and !=} can be used to define the conditions of a constraint
All the constraints for a State are subject to an AND operation unless otherwise specified; you can use the OR operation on them instead, so you could rewrite the constraints in the example as:
Location=0 OR
Location=1 AND
Departing.Name!=Central
Here are some examples of using the equivalence operators:
Departing.Name!=Central AND
Location!=1
Notes
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