event.ClassInstanceEvent - Event data for InstanceCreated and InstanceDestroyed events - MATLAB (original) (raw)

Namespace: event
Superclasses: event.EventData

Event data for InstanceCreated and InstanceDestroyed events

Description

This class defines the event data that is passed to listeners of thematlab.metadata.Class InstanceCreated and InstanceDestroyed events.

The event.ClassInstanceEvent class is a handle class.

Class Attributes

For information on class attributes, see Class Attributes.

Creation

MATLAB® creates an event.ClassInstanceEvent object when triggering a InstanceCreated or InstanceDestroyed event.

Properties

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Object being created or deleted.

Attributes:

Data Types: object

matlab.metadata.Class object that is the source of the event, returned as a matlab.metadata.Class object.

Attributes:

Name of the event, returned as a character vector that is either InstanceCreated or InstanceDestroyed.

Attributes:

Data Types: char

Examples

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Use matlab.metadata.Class events to count the number of instances as objects are created and destroyed.

Create a class with a callback function for the InstanceCreated andInstanceDestroyed events. The eventCallback static method uses a persistent variable to store the number of instances of the class that exist. The addEventListeners method adds the listeners to thematlab.metadata.Class object for the CountInstances class.

classdef CountInstances methods (Static) function eventCallback(~,eventData) % Callback for InstanceCreated and InstanceDestroyed persistent instanceCount if ~isempty(instanceCount) switch eventData.EventName case "InstanceCreated" instanceCount = instanceCount + 1; case "InstanceDestroyed" if ~instanceCount == 0 instanceCount = instanceCount - 1; end end else instanceCount = 1; end fprintf('%s %d \n',... 'Number of Instances: ',instanceCount) end function addEventListeners(mc) % Add listeners addlistener(mc,"InstanceCreated",... @(src,evnt)CountInstances.eventCallback(src,evnt)); addlistener(mc,"InstanceDestroyed",... @(src,evnt)CountInstances.eventCallback(src,evnt)); end end end

Create a matlab.metadata.Class object for theCountInstances class and add listeners for theInstanceCreated and InstanceDestroyed events. This example uses the same callback for both events.

mc = ?CountInstances; CountInstances.addEventListeners(mc)

Whenever you create or destroy an object of the CountInstances class, the event causes an update to the instanceCount persistent variable.

Use matlab.metadata.Class events to observe the creation and destruction of objects

Create a class with a callback function for the InstanceCreated andInstanceDestroyed events. The eventCallback static method serves as the callback function for both events. TheaddEventListeners method adds the listeners to thematlab.metadata.Class object for the ClassInstanceEvent class.

classdef ClassInstanceListeners properties Prop end methods function obj = ClassInstanceListeners(p) obj.Prop = p; end end methods (Static) function eventCallback(~,eventData) % Callback for InstanceCreated and InstanceDestroyed I = eventData.Instance; S = eventData.Source; E = eventData.EventName; dashLine = sprintf('%s\n','--------------------'); fprintf('%s',dashLine) fprintf('%s \n',['Class: ',class(I)]) fprintf('%s %d \n',[S.PropertyList.Name ': '],I.Prop) fprintf('%s%s \n','Event: ', E) fprintf('%s',dashLine) end function addEventListeners(mc) % Add listeners addlistener(mc,"InstanceCreated",... @(src,evnt)ClassInstanceListeners.eventCallback(src,evnt)); addlistener(mc,"InstanceDestroyed",... @(src,evnt)ClassInstanceListeners.eventCallback(src,evnt)); end end end

Create a matlab.metadata.Class object for theCreateInstanceListeners class and add listeners for theInstanceCreated and InstanceDestroyed events. This example uses the same callback for both events. Construct an instance of theCreateInstanceListeners class and assign an identifier to the propertyProp.

mc = ?ClassInstanceListeners; ClassInstanceListeners.addEventListeners(mc) obj = ClassInstanceListeners(1334);

Class: ClassInstanceListeners Prop: 1334 Event: InstanceCreated

Constructing another instance that is assigned to the same variable creates a new object and destroys the old object.

obj = ClassInstanceListeners(7335);

Class: ClassInstanceListeners Prop: 7335 Event: InstanceCreated

Class: ClassInstanceListeners Prop: 1334 Event: InstanceDestroyed

If you modify the class definition, MATLAB deletes the matlab.metadata.Class object because it is no longer a valid description of the class. After modifying the class, you must create a new matlab.metadata.Class object and add listeners to it.

Version History

Introduced in R2008a