handlePropEvents method not recognized

Dear MATLAB Community

I have a class Plot with observable properties and a handlePropEvents static method. However, when I create an instance of a derived class TimeSpace and change a property there, MATLAB returns a warning that Plot.handlePropEvents is undefined. Does someone have any idea what could be the problem?

Thanks for any hints.

This is the base class:

classdef Plot < handle

    properties(SetObservable)
        titleString = 'No Title';
        xLabel = 'xLabel';
    end
    
    methods
        
        function obj = Plot(figureSize)
            % Some code here
        end
 
    end

    methods(Static)
        
        function handlePropEvents(src, event)
            
            obj = event.AffectedObject;
            switch src.Name
                case 'titleString'
                    title(obj.titleString);
                case 'xLabel'
                    xlabel(obj.xLabel);
            end
            
        end
        
    end
        
end

And this is the derived class where we change the properties:

classdef TimeSpace < Plot.Plot

    properties
    end
    
    methods
        
        function obj = TimeSpace(lineTable)
            [e-mail]();
            obj.setEnvironment(lineTable.data);
        end
        
        function setEnvironment(obj, line)
            obj.titleString = 'Abbildung A.14'
            obj.xLabel = 'Stunden';
        end
        
    end
    
end

This is the warning (LoadCarped is just another derived class from TimeSpace):

Warning: Error occurred while executing the listener callback for the Plot.LoadCarpet class xLabel
property PostSet event:
Undefined function 'Plot.handlePropEvents' for input arguments of type 'meta.property'. 
> In Plot/TimeSpace/setEnvironment (line 28)
In Plot/TimeSpace (line 17)
In Plot.LoadCarpet (line 13)
In Plot.plotAll (line 51)
In Scenario/runPlots (line 103)
In Scenario/runAnalysis (line 97)
In Scenario/runShunting (line 91)
In Scenario/runDemand (line 85)
In Scenario/runVehicles (line 74)
In Scenario/runTimetable (line 68)
In Scenario/run (line 44)
In Scenario (line 39)
In main (line 12) 

Answer 1

[TARUN]

Hi @Lukas Ballo,

The issue is because the handlePropEvents method is not connected to the observable properties. In MATLAB, when you want to react to changes in observable properties, you need to add a listener “addlistener” to those properties in the constructor of the class.

The handlePropEvents method won't be automatically called when a property changes if there are no property listeners.

You can learn more about the listeners here: https://www.mathworks.com/help/matlab/matlab_oop/listening-for-changes-to-property-values.html

Here is the updated code of both classes with listeners:

classdef Plot < handle 
    properties(SetObservable) 
        titleString = 'No Title'; 
        xLabel = 'xLabel'; 
    end 
    methods  
        function obj = Plot(figureSize) 
            addlistener(obj, 'titleString', 'PostSet', @Plot.handlePropEvents); 
            addlistener(obj, 'xLabel', 'PostSet', @Plot.handlePropEvents); 
        end 
    end 
    methods(Static) 
        function handlePropEvents(src, event) 
            obj = event.AffectedObject; 
            switch src.Name 
                case 'titleString' 
                    title(obj.titleString); 
                case 'xLabel' 
                    xlabel(obj.xLabel); 
            end    
        end 
    end 
end 

classdef TimeSpace < Plot 
    properties 
    end 
    methods 
        function obj = TimeSpace(lineTable) 
            % Call the parent class constructor 
            obj@Plot(lineTable.data); 
            obj.setEnvironment(lineTable.data); 
        end 
        
        function setEnvironment(obj, line) 
            obj.titleString = 'Abbildung A.14'; 
            obj.xLabel = 'Stunden'; 
        end 
    end 
end 

With this code the Title and x-label will be updated due to the property listeners.