event.PropertyEvent - Data for property events - MATLAB (original) (raw)

Namespace: event

Description

The event.PropertyEvent class defines the event data objects passed to listeners of the predefined property events PreGet,PostGet, PreSet, andPostSet. Predefined property events enable listeners to respond to changes made to property values. For more information, see Listen for Changes to Property Values.

The event.PropertyEvent class is a sealed subclass ofevent.EventData (that is, you cannot subclassevent.PropertyEvent). The class constructor is private. MATLAB® creates an event.PropertyEvent object to pass to listeners of property events.

The event.PropertyEvent class is a handle class.

Class Attributes

For information on class attributes, see Class Attributes.

Properties

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Object whose property is affected, specified as the object handle.

Attributes:

Data Types: handle object

Property that triggers the event, specified as thematlab.metadata.Property object for the property.

Attributes:

Name of the property event, specified as one of the four event names.

Attributes:

Data Types: char

Examples

Listen for Property Event

Define the propEventClass class with thePropOne GetObservable and SetObservable attributes enabling observation of property events. The class constructor adds listeners for these events.

classdef propEventClass < handle % Class to observe property events properties (GetObservable,SetObservable) PropOne string = "default" end methods function obj = propEventClass addlistener(obj,'PropOne','PreGet',@propEventHandler); addlistener(obj,'PropOne','PostSet',@propEventHandler); end end end

The propEventHandler function serves as the callback for thePreGet and PostSet events.

The event.PropertyEvent object Source property contains the matlab.metadata.Property object forPropOne. Access thematlab.metadata.Property Name property to get the name of the property on which the event is triggered. Switch on the property name when the callback handles multiple properties.

The event.PropertyEvent object EventName property contains the name of the event. To handle multiple property events from the callback, switch on the event name.

function propEventHandler(~,eventData) switch eventData.Source.Name % Get property name case 'Prop1' switch eventData.EventName % Get the event name case 'PreGet' fprintf('%s\n','PreGet triggered') case 'PostSet' fprintf('%s\n','PostSet triggered') disp(eventData.AffectedObject.(eventData.Source.Name)); end end end

Referencing the PropOne property value results in a response from the propEventHandler to the PreGet event.

obj = propEventClass; obj.PropOne

PreGet triggered

ans =

"default"

Assigning to the PropOne property results in a response from the propEventHandler to the PostSet event.

Because the callback gets the property value to display the new value after thePostSet event, the PreGet event is triggered. Also, because the assignment statement is not terminated by a semicolon, MATLAB gets the property value to display the object in the command window, which triggers the PreGet event again.

obj.PropOne = "New string"

PostSet triggered PreGet triggered New string

obj =

PreGet triggered propEventClass with properties:

PropOne: "New string"

Version History

Introduced in R2008a