Referencing an object property within the set method for a different property

I have the following custom class definition:

classdef PlotParameters < handle
    % properties that affect how data is plotted
    properties
        Prop1 (1,1) double
        Prop2 (1,1) double
    end
    
    % properties that don't affect how data is plotted
    properties
        Prop3 (1,1) string
        Prop4 (1,1) string
    end
    
    % The HoldUpdatePlot private property is set to true by class methods
    % that updated multiple properties at once. When this property is true,
    % the UpdatePlot event is not fired. When this property is changed from
    % true to false, the UpdatePlot event is always fired (see the set
    % method for HoldUpdatePlot).
    properties (Access = private)
        HoldUpdatePlot (1,1) logical = false
    end
    
    
    % The UpdatePlot event is fired whenever the object properties that
    % affect how data is plotted (i.e. Prop1 and Prop2) are updated.
    events
        UpdatePlot
    end
    
    
    % CONSTRUCTOR METHOD
    methods
        function obj = PlotParameters(opt)
            arguments
                opt.Prop1 (1,1) double = 1
                opt.Prop2 (1,1) double = 1
                opt.Prop3 (1,1) string = ""
                opt.Prop4 (1,1) string = ""
            end
            
            obj.HoldUpdatePlot = true;
            obj.Prop1 = opt.Prop1;
            obj.Prop2 = opt.Prop2;
            obj.Prop3 = opt.Prop3;
            obj.Prop4 = opt.Prop4;
            obj.HoldUpdatePlot = false;
        end
    end
    
    % PROPERTY SET METHODS
    methods
        function set.Prop1(obj, NewProp1Value)
            arguments
                obj (1,1) PlotParameters
                NewProp1Value (1,1) double
            end
            % fires the UpdatePlot event
            obj.Prop1 = NewProp1Value;
            if ~obj.HoldUpdatePlot
                notify(obj,'UpdatePlot');
            end
        end

        function set.Prop2(obj, NewProp2Value)
            arguments
                obj (1,1) PlotParameters
                NewProp2Value (1,1) double
            end
            % fires the UpdatePlot event
            obj.Prop2 = NewProp2Value;
            if ~obj.HoldUpdatePlot
                notify(obj,'UpdatePlot');
            end
        end

        function set.HoldUpdatePlot(obj, NewHoldUpdatePlotValue)
            % fires the UpdatePlot event when HoldUpdatePlot is switched from true to false
            arguments
                obj (1,1) PlotParameters
                NewHoldUpdatePlotValue (1,1) logical
            end
            if ~NewHoldUpdatePlotValue && obj.HoldUpdatePlot
                obj.HoldUpdatePlot = NewHoldUpdatePlotValue;
                notify(obj,'UpdatePlot');
            else
                obj.HoldUpdatePlot = NewHoldUpdatePlotValue;
            end
        end
    end
    
    
    % GENERAL METHODS
    methods
        function ResetAllProperties(obj)
            % resets all properties to their default values
            arguments
                obj (1,1) PlotParameters
            end
            obj.HoldUpdatePlot = true;
            obj.Prop1 = 1;
            obj.Prop2 = 1;
            obj.Prop3 = "";
            obj.Prop4 = "";
            obj.HoldUpdatePlot = false;
        end
    end
end

The idea is that I can have an external listener for the UpdatePlot event which will replot data when the relevant properties of the PlotParameters object are updated:

>> PlotParametersObject = PlotParameters();

>> addlistener(PlotParametersObject,'UpdatePlot',@(src,evnt)disp("Property changed - data will be replotted!"));

>> PlotParametersObject.Prop1 = 5;

Property changed - data will be replotted!

However, if multiple properties are being updated at once, I don't want the UpdatePlot event to be fired more than once. So there is a private property ("HoldUpdatePlot") that will prevent the UpdatePlot event from firing if it is set to true. This is used by class methods such as ResetAllProperties to stop the UpdatePlot event from firing until all property updates have been made:

>> PlotParametersObject.ResetAllProperties();

Property changed - data will be replotted!

Notice how only one notification is printed, even though multiple properties were updated.

Although the code is working as intended, MATLAB shows warnings in the set methods for Prop1 and Prop2 (on lines 59 and 71). These set methods reference a property other than the property being set (HoldUpdatePlot), and the text of the warning is the following:

I tried saving and loading a PlotParameters object to/from a file, and I didn't have any issues. However, the language in the warning suggests that that might not always be the case. Unfortunately, I really need to prioritize stability with this code, and the possiblity of it working one day and then not working the next day is not acceptable.

I can't think of a different way to structure the class which would avoid the warning while still achieving the functionality I need. Is there anyone out there who's smarter than I am and can suggest a better way to do what I'm trying to do?

Alternatively, is there anyone out there who can say difinitively, "That code will always work - you should just ignore the warning"?

Answer 1

[Matt J]

This may seem cumbersome to you, but the robust way to deal with this is to make any property that can trigger an event Dependent. Because Dependent properties are not set when loading an object from a file, you don't need to worry about any kind of event sequencing in that circumstance. For brevity's sake, I illustrate for only one such property Prop1:

classdef PlotParameters < handle
    % properties that affect how data is plotted
    properties (Hidden,Access=private)
        Prop1_ (1,1) double  %Holdd the data for Prop1
    end
    properties (Access=private)
        HoldUpdatePlot (1,1) logical = false
    end
    properties (Dependent)
       Prop1 
    end
    
    function val=get.Prop1(obj)
        val=obj.Prop1_;
    end
    
    function set.Prop1(obj, NewProp1Value)
        arguments
            obj (1,1) PlotParameters
            NewProp1Value (1,1) double
        end

        obj.Prop1_ = NewProp1Value;
        if ~obj.HoldUpdatePlot
            notify(obj,'UpdatePlot');
        end
    end   
    
end
    

[DBFun]

You're right - that is cumbersome. But it works, and that's really what matters. Thanks for your help.

Answer 2

[Matt J]

You can create a processNotification() method and do all the necessary property referencing there instead:

        function processNotification(obj)
        
            if ~obj.HoldUpdatePlot
                notify(obj,'UpdatePlot');
            end

        end
        function set.Prop1(obj, NewProp1Value)
            arguments
                obj (1,1) PlotParameters
                NewProp1Value (1,1) double
            end
            % fires the UpdatePlot event
            obj.Prop1 = NewProp1Value;
            
            processNotification(obj);
        end

        function set.Prop2(obj, NewProp2Value)
            arguments
                obj (1,1) PlotParameters
                NewProp2Value (1,1) double
            end
            % fires the UpdatePlot event
            obj.Prop2 = NewProp2Value;

            processNotification(obj);
        end

[DBFun]

Matt J - before I say anything else, I appreciate you taking the time to look at this. Thank you!

Adding the processNotification wrapper function does work to eliminate the warning. However, after thinking it through, I suspect it's doing it more by tricking the MATLAB editor rather than by addressing the root cause of the issue.

If I understand the warning correctly, MATLAB doesn't guarantee that the HoldPlotUpdate property will always be initialized before the Prop1 and Prop2 properties when loading a PlotParameters object from a file. So if Prop1 or Prop2 gets initialized first (which will result in a call to the set method for Prop1 or Prop2), and the HoldPlotUpdate property hasn't been initialized yet, then the whole load operation could blow up when the set method tries to retrieve the (uninitialized) value of HoldPlotUpdate. It seems to me that this would happen regardless of whether the reference to HoldPlotUpdate is in the set method itself, or burried in the processNotification sub-method.

After going through that thought exercise, another possibility occurred to me. It may be possible to do something with a custom load method that forces MATLAB to initialize the properties in a certain order when loading an object from a file. I'm not sure what that would look like yet, but if it works, then I could just ignore the warnings.

[Matt J]

I notice that there are no plot handle properties in your classdef. Shouldn't there be, since all this seems to be geared toward plot management?

If you had a handle property, you could have the processNotification() method first check if the handle (i.e., if the plot is exists), and abort if not. Then the status of the HoldPlotUpdate property wouldn't matter.

[DBFun]

Under normal circumstances, that would work, yes. However, in this case, the example class I provided above is a component of a fairly intricate app. The concept for the app is that there there can be multiple types of source object for each plot (for example, a PlotParameters object, a PlotData object, etc) and an update to any one of the source objects would force the related plot to update. An additional intention is that multiple plots can point to the same source object(s), which means that an arbitrary number of plots may need to update when a source object is altered. I would much rather manage the whole system by just having the individual plots listen for changes in their source object(s), as opposed to having the source objects maintain arrays of handles for the plots they are linked to.