Using findobj() on Heterogeneous handle object array

Hello,

I ran into a problem when working with heterogenous class hierarchies. I created a superclass Body which is derived from handle and matlab.mixin.Heterogeneous :

classdef Body < matlab.mixin.Heterogeneous
    ...
end
%-----------------------------------
classdef RigidBody < Body
    ...
end
%-----------------------------------
classdef FlexBody < Body
    ...
end

The problem that I now ran into came when I combine these two derived classes in a heterogenous array from the class Body. I can't use the function findobj() on that array to find an object with a specific property value,

When trying to find an object with a specific object property whichw as defined in the Body class

% init heterogenous array a
a(1) = RigidBody(...)
a(2) = FlexBody(...)

% find body with name body_1
findobj(a, 'name', 'body_1')

I get the error message

Error using Body/findobj
Unable to call method 'findobj' because one or more inputs of class 'Body' are heterogeneous and 'findobj' is not sealed.  For more
details please see the method dispatching rules for heterogeneous arrays.

Is there any kind of work around, since findobj is a method inhereted by the handle class and I therefore can't just seal it.

Thanks!

Answer 1

[Adarsh]

Hi @Lennart Scherz,

I have faced a similar issue calling an unsealed function on an array of Heterogeneous objects.

This issue occurs because functions that are applied on heterogeneous object arrays needed to be sealed in the base class to ensure uniformity of the function around all the elements by preventing the subclassing of the sealed functions.

Here is an alternate workaround that worked for me:

1. Wrap the original “findobj” function inside another function in base class.
2. Seal the wrapper function.
3. Inside the wrapper function apply the “findobj”function to each element using a for loop or “arrayfun”individually.

Here is a sample code demonstrating the workaround:

classdef Body < matlab.mixin.Heterogeneous & handle
    properties
        name
    end
    
    methods (Sealed)
        function obj = findBodyByName(objArray, varargin)
            % Initialize a logical array to store matches
            matches = false(size(objArray));
            
            % Loop through each element in the array
            for i = 1:numel(objArray)
                % Use findobj on each individual element with varargin
                foundObj = findobj(objArray(i), varargin{:});
                
                % Check if findobj found anything
                if ~isempty(foundObj)
                    matches(i) = true;
                end
            end
            
            % Return the objects that match the criteria
            obj = objArray(matches);
        end
    end
end

For more information on heterogeneous object arrays please refer to the following documentation link:

https://www.mathworks.com/help/matlab/matlab_oop/heterogeneous-arrays.html

I hope this helps.