MATLAB: How to find all object of a certain handle class

find objectshandle classMATLABoop

I need to find all current object memory instances of a certain handle class "MyClass".

I cannot use "findobj" because I do not have a "seed" handle.

using "whos" is also problematic because: (a) different variables can in fact point to the exact same object; (b) objects may exist without any variable poitnitng to them (for example objects that are pointed to from a "UserData" of a figure); (c) handles to soem objects may be held in persitence variables of a static method of the class.

is there a generic way to find all the objects of MyClass despites these listed difficulties?

Best Answer

I don't think there's any way to track down instances after the fact.

You could however track the creation and deletion of all instances of any handle class, without changing the class code, with meta.class and the events InstanceCreated and InstanceDestroyed. The whole thing is badly documented but the 2nd argument of the event is of type ClassInstance whose one of the property is the object created/destroyed.

Unfortunately, for the Destroyed case, the handle is no longer valid by the time you get it (since the object has been destroyed), so overall, I'm not sure it's that useful. Still, you could keep a reference count of object creation and destruction to know how many are in memory.

Related Solutions

MATLAB: Suppressing superclass methods/events

This is the best you can do to hide the methods which are relared to handle (here superclass). All te methods are hidden except 'isvalid' which is a sealed method of 'handle' class.

classdef myClass < handle
    methods
        function O = myClass()
            
        end
    end
    methods (Hidden)
        function varargout = findobj(O,varargin)
            varargout = findobj@handle(O,varargin);
        end
        function varargout = findprop(O,varargin)
            varargout = findprop@handle(O,varargin);
        end
        function varargout = addlistener(O,varargin)
            varargout = addlistener@handle(O,varargin);
        end
        function varargout = notify(O,varargin)
            varargout = notify@handle(O,varargin);
        end
        function varargout = listener(O,varargin)
            varargout = listener@handle(O,varargin);
        end
        function varargout = delete(O,varargin)
            varargout = delete@handle(O,varargin);
        end
    end
end

MATLAB: Add a event callback across all instances of class?

What you're trying to create is a static property (belongs to the class not the instances). Matlab does not have that, but you could possibly emulate it with a constant property holding a reference to a handle class. Either make a lightweight handle class to wrap your static property or simply use a containers.Map with only one key:

classdef classwithstaticprop < handle
  properties (Constant, GetAccess = private)
      staticprop = containers.Map; %or just make a lightweight handle class
  end
    properties (Dependent)
        sharedprop
    end
    methods
        function this = classwithstaticprop() %constructor
            if length(this.staticprop) == 0 %#ok<ISMT> isempty not defined for map
                %first instance, initialise;
                m = this.staticprop; %you have to use a local variable, see the doc
                m('prop') = 1; %#ok<NASGU> %initialise to default value
            end
        end
        function set.sharedprop(this, value)
            m = this.staticprop;
            m('prop') = value; %#ok<NASGU> %it's a handle
        end
        function value = get.sharedprop(this)
            value = this.staticprop('prop');
        end
    end
  end

See this page for why you have to use a local variable when changing the value of the handle class referred by the constant property.

Best Answer

Related Solutions

MATLAB: Suppressing superclass methods/events

MATLAB: Add a event callback across all instances of class?

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