Instantiating an invalid handle object when defining an object as default property definition

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Jacob Lynch August 2020-3-13

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https://ww2.mathworks.cn/matlabcentral/answers/510751-instantiating-an-invalid-handle-object-when-defining-an-object-as-default-property-definition

编辑： Jacob Lynch August 2020-3-13

A classdef defines some properties which are defined, but have no valid construction. E.g. an event.proplistener. In the example below, this class cannot be instantiated, generating the following error.

Error defining property 'Listener' of class 'egPropWithListener':

No constructor 'event.proplistener' with matching signature found.

This property could contain a deleted handle to an event.proplistener object. Is there a way to create a "pre-deleted" handle of an object?

classdef egPropWithListener < handle
    properties(SetObservable,AbortSet)
        Prop1 (1,1) double = 0;
    end
    properties(Access=protected)
        % This listener monitors Prop1, and will  
        Listener (1,1) event.proplistener
    end
    methods
        function obj = egPropWithListener()
            obj.Listener = addlistener(obj,'Prop1','PostSet',@egPropWithListener.postSetPropAction);
        end
    end
    methods(Static)
        function postSetPropAction(prop_dat,event_dat)
            obj = event_dat.AffectedObject;
            % some actions ... 
            % if condition met ...
            obj.Listener.Enable = false;
            % ... stop listening.
        end
    end
end

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Jacob Lynch August 2020-3-13

编辑：Jacob Lynch August 2020-3-13

My colleagues that don't use MATLAB struggle with it's syntax. My current workarounds for their benefit, which I don't favor, involve relaxing the type or size defintion.

classdef egPropWithListener < handle
    % ...
    properties
        % relax the type definition
        AltDef1 (1,1) % event.proplistener
        
        % relax the size defintion
        AltDef2 (1,:) event.proplistener
        % initiates with an empty vector of listeners, like event.proplistener.empty(1,0)
    end
end