Implement Property Set Listeners

R2026b

This example shows how to define a listener for a property set event. The listener triggers when the value of the specified property changes. The callback function of the listener then updates a figure based on that property change.

DataSetWithPlot Class Overview

This class DataSetWithPlot defines a Data property that holds a 2-by-n array of numeric data. The visualize method plots the values in Data and also defines a listener to respond to changes in Data. The callback function updateFigureData updates the plot with the new data.

classdef DataSetWithPlot < handle
    properties (SetObservable)
        Data (2,:) {mustBeNumeric}
    end

    methods
        function obj = DataSetWithPlot(initialData)
           obj.Data = initialData;
        end
        
        function visualize(obj)
            f = plot(obj.Data(1,:),obj.Data(2,:));
            dataChangedListener = listener(obj,"Data","PostSet",@(~,evtData)updateFigureData(f,evtData.AffectedObject.Data));
            f.UserData = dataChangedListener;
        end
    end
end

function updateFigureData(fig,data)
    fig.XData = data(1,:);
    fig.YData = data(2,:);
end

Event and Listener Design

The Data property is defined with the attribute SetObservable set to true, enabling listeners to respond to changes in its value. After plotting the data, the visualize method defines the listener dataChangedListener and assigns that listener to the UserData property of the figure..

dataChangedListener = listener(obj,"Data","PostSet",@(~,evtData)updateFigureData(f,evtData.AffectedObject.Data));
f.UserData = dataChangedListener;

• The listener object, dataChangedListener, is defined using the listener method of handle. The listener responds to the PostSet event for the Data property. PostSet is a predefined MATLAB^® event that fires after the value of a property is set.

• The callback function, updateFigureData, updates an existing plot with the new data. The callback function does not need any information from the source argument (which in this case is the matlab.metadata.Property instance for the Data property), so the listener does not pass that information to the callback. The callback takes the handle for the figure (f) and the new value for Data as inputs. The value of Data is passed in through an instance of event.PropertyEvent, which holds a DataSetWithPlot instance in its AffectedObject property.

• Unlike the addlistener method, the listener method does not bind the listener lifecycle to the event source. The listener object is stored in the UserData property of the figure, so when the figure is deleted, the listener is also deleted.

Test DataSetWithPlot

Create a DataSetWithPlot instance and call the visualize method.

d = DataSetWithPlot([0 2; 0 2]);
d.visualize

Change the Data property of d. The PostSet event fires and the listener calls updateFigureData. The existing figure is updated with the new value of Data.

d.Data = [0 1.6 2; 0 1 2];