Why is event PreUpdate and PostUpdate not triggered in ChartContainer?

Hi all,

I’ve created a ChartContainer in MATLAB R2024b and need to track when its update routine finishes so I can restore an internal property to its original value. During setup, I added listeners for the PreUpdate and PostUpdate events of the ChartContainer.

However, when I change a property, the update method runs, but neither the PreUpdate nor PostUpdate events seem to fire.

Below I share the class implementation:

classdef TestComponent < matlab.graphics.chartcontainer.ChartContainer
    
    %% Properties
    properties (AbortSet)

        % Internal use. Indicates update is required, triggered by external
        % property.
        TriggerUpdate (1,1) logical = false;

    end %properties

    properties (Transient, NonCopyable, Hidden, SetAccess = protected, UsedInUpdate = false)

        % Event listener array
        EventListeners (1,:) event.listener

    end
    
    %% Protected Methods
    methods (Access = protected)

        function setup(obj)
            % Setup routine

            % Show setup routine is executed
            disp('setup')

            % Setup listeners to all events in the class
            metaClass = meta.class.fromName(class(obj));
            eventList = {metaClass.EventList.Name};
            listenAcces = {metaClass.EventList.ListenAccess};

            % Initialize listener to post-update event
            for idx = 1:numel(eventList)
                if ~strcmpi(listenAcces{idx}, {'public', 'protected'})
                    continue
                end
                obj.EventListeners(end+1) = listener(obj, ...
                    eventList{idx}, @(s,e) obj.showEvent(e));
            end
        end %function
        
        function update(obj)
            % Update routine

            % Show update routine is executed
            disp('update')
        end %function

    end %methods

    methods

        function showEvent(obj, e)
            disp(e)
        end %function

    end %methods
end

Does anyone know why these events aren’t triggered? For ComponentContainer, the events work as expected.

Answer 1

[Aditya]

Hi Jacob,

You have observed correctly: PreUpdate and PostUpdate events are available and documented for ComponentContainer (UI components), but not for ChartContainer (axes-based charts).Why aren't PreUpdate/PostUpdate firing in ChartContainer?

• ChartContainer does not define or fire PreUpdate/PostUpdate events.
• The MATLAB documentation for ComponentContainer explicitly lists these events, but the ChartContainer documentation does not.
• This is by design: ChartContainer update cycle is not evented in the same way as ComponentContainer.

You can try the following steps:

• Override the update method and place your logic before and after calling the superclass update, if needed.
• If you need to execute code after every update, do it at the end of your update method.
• If you have code that should run before an update, do it at the beginning of update.

Answer 2

[Andrew Ouellette]

Hi @Jacob-Jan Sloots,

I can't give you a great answer as to why the behavior differs between ChartContainer and ComponentContainer. However, I expect that you can achieve the behavior you desire without needing to create listeners to undocumented events.

In particular, you mention that you want to perform some clean up action after "update" has finished. Could you just place your clean up functionality at the bottom of the update function?

I imagine you could have an implementation like the following:

classdef TestComponent < matlab.graphics.chartcontainer.ChartContainer
    methods (Access=protected)
        function setup(this)
            % You can often leave this method empty
        end
        function update(this)
            preUpdate(this);
            % Insert your current update code here
            postUpdate(this);            
        end
        function preUpdate(this)
            % Setup transient data for update
        end
        function postUpdate(this)
            % Cleanup transient data from update
        end
    end
end