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Knowledge Modeler |
Subscribing to EventsHow to be warned when events occur on parameters |
| Use Case | ||
AbstractAn event is an object that notifies another that an event has occurred. This article explains how to subscribe to the events supported by the KnowledgeInterfaces framework. |
This article explains how to subscribe to "change value", "change visu" and "delete" events.
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The LiteralFeatures platform supports four types of events which are described by the CATIParrnEvents interface. These events are:
When designing a literal-based application, if you want to be warned whenever a parameter is modified, you must: be provided with a feature whose purpose is to observe or detect the parameter modifications. This feature must subscribe to the events supported by the LiteralFeatures platform.
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CAALifEvents is a use case of the CAALiteralFeatures.edu framework that illustrates KnowledgeInterfaces framework capabilities.
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This use case:
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To launch CAALifEvents, you will need to set up the build time environment, then compile CAALifEventsMain along with its prerequisites, set up the run time environment, and then execute the use case which main program is CAALifEventsMain [1].
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The CAALifEvents use case is located in:
| Windows | InstallRootDirectory\CAALiteralFeatures.edu\CAALifEvents.m\ |
| Unix | InstallRootDirectory/CAALiteralFeatures.edu/CAALifEvents.m/ |
where InstallRootDirectory is the directory where the CAA
CD-ROM is installed.
The main program related to this use case is CAALifEventsMain.
An implementation of the CAAILifMyFeatureEvents interface is defined in the CAALifMyFeatureEventsExt extension of the CAAMyFeature late type. The interface is defined in the PrivateInterfaces directory, the implementation is defined in the CAALifEvents.m module.
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Here is the step-by-step description of the program:
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The CATICkeParmFactory is retrieved from the document container. For more information on the purpose of this factory, see [2].
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A Length type parameter is created. This parameter is assigned a 1m initial value. Let's remind you that the value you pass in the argument of a CreateLength method is read as an SI unit. This also applies to other literal creation methods. The parameter which is created is the one we are going to "observe". In other words its is going to subscribe to the events managed by the KnowledgeInterfaces framework.
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The current unit of the "Length" parameter is specified as the first item of the list which is displayed in the Tools->Options->Units for parameters of Length type. In our example, the first unit in the list of units for Length type parameter is the mm. Depending on your application settings, you may get a different unit when displaying a parameter value. For more information, see [3].
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The "CAAMyfeature" StartUp is created. The CAAMyFeature late type is defined in the CAALifBasis.m module. The CAALifMyFeaturesEventsExt extension provides an implementation of the CAAILifMyFeatureEvents interface which is defined in the PrivateInterfaces directory.
About the CAAILifMyFeatureEvents::Observe method:
This method which is implemented in the CAALifMyFeaturesEventsExt.cpp extension
uses the CATInterfaceEvents::AddSubscription method defined in the
ObjectModelerBase framework.
virtual CATCallback AddSubscription( CATInterfaceEvents *eventManager,
CATCallbackEvent event,
CATSubscriberMethod method,
char *interfaceID,
CATSubscriberData data = NULL ) = 0 ;
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Writing the instruction below:
spSpev->AddSubscription(spParameterEvents,
spParameterEvents->GetChangeValueNotification(),
(CATSubscriberMethod)&CAAILifMyFeatureEvents::IfChangeValue,
"CAAILifMyFeatureEvents",
(CATSubscriberData) this);
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means that the parameter the Observe method is applied to calls the service defined in the third argument (IfChangeValue) when the event specified in the second argument occurs. The CAAILifMyFeatureEvents::IfChangeValue method is defined in CAALifMyFeatureEventsExp::Observe extension. It just increments a counter and displays a message in the standard output whenever the parameter value is modified.
Subscriptions to "delete" and "change visu" events are patterned on the same principle.
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The "OBJ0" instance is created from the "CAAMyFeature" StartUp.
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Subscribe to the three events defined in the CAAILifMyFeatureEvents::Observe method and implemented in the CAALifMyFeatureEventsExt extension. From this point, all the "change value", "change visu" and "delete" events should issue a message and increment the counters defined in the Observe method.
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The "Length" parameter value is replaced with 30 mm. let's remind you that when you use the CATICkeParm::ValuateStored method the value specified in the argument is the document default unit (i.e. mm for length parameters). Upon modification of the "Length" parameter, the counter which record the "change value" events increments. The statements below:
spStore->ValuateStored (30); cout << "The p1 value is " << spLength->Show().CastToCharPtr() << endl; |
display in the standard output:
Receiving ChangeValue number 1 The p1 value is 30mm |
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The number of "change value" notifications is displayed. As expected, 1 notification has been recorded.
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The access rights of the "Length" parameter are modified. A "change visu" notification should be issued. The statements below:
spLength->SetUserAccess(CATICkeParm::ReadOnly);
cout << "Number of \"change visu\" notifications (1 is expected) " ;
cout << CAALifMyFeatureEventsExt::nbchangevisu << endl;
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display in the standard output:
Receiving ChangeVisu number 1 Number of "change visu" notifications (1 is expected) 1 |
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The current unit of the "Length" parameter is modified. A "change visu" notification should be issued. The statements below:
spMag->SetCurrentUnit ((*(spMag->Units()))[2]); cout << "The p1 value is " << spLength->Show().CastToCharPtr() << endl; |
display in the standard output:
Receiving ChangeVisu number 2 The p1 value is 0.03m |
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The number of "change visu" notifications is displayed. As expected, 2 notifications have been recorded.
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The "Length" parameter is deleted. The statements below:
spLco->remove(); cout << "Number of \"delete\" notifications (1 is expected) " ; cout << CAALifMyFeatureEventsExt::nbdelete << endl; |
display in the standard output the following messages
Receiving Delete number 1 Number of "delete" notifications (1 is expected) 1 |
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The CAAILifMyFeatureEvents object is deleted. Note that is strongly recommended to delete an event object after all objects it was intended to be applied have been deleted.
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Four types of events are supported by the LiteralFeatures platform:
When developing an application, subscribing to events requires a feature dedicated to the detection of parameter modifications.
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| [1] | Building and Launching a CAA V5 Use Case |
| [2] | Getting Started with Literal Feature Programming |
| [3] | About Units |
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| Version: 1 [Jan 2000] | Document created |
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Copyright © 2000, Dassault Systèmes. All rights reserved.