Cannot allocate this handle object. For code generation, a handle object allocated inside a loop cannot be referenced outside of the loop

Here is my code snippet. Is there any workaround other than changing the handle object to a value class?

classdef ImageWrapper < handle%#codegen
    %IMAGEWRAPPER 对img matrix的wrapper类，提供常用的接口函数，尽可能避免上层代码对img matrix直接的索引操作。
    % 图像的宽高等常用信息也可以直接通过imgShape这个属性获取。
    %   此处显示详细说明
    
    properties
        img (:,:) double % 管理的img matrix像素矩阵信息
        flag_unset (:,:) double % 像素位置未设置标志位，初始化为全1
        imgShape (1,1) ImgShape % 图像宽、高信息
    end
    
    methods
        function this = ImageWrapper(img)
            arguments 
                img (:,:) double = []
            end
            this.img = img;
            this.flag_unset = ones(size(img));
            this.imgShape = ImgShape(size(img,2),size(img,1));
        end

        function multiply_in_place(this,valueMatrix)
            this.img(:) = this.img .* valueMatrix;
        end
       
        function this = setAtMatrixRange(this,matrixRange,valueMatrix)
            %SETATMATRIXRANGE 将图像对应于matrixRange的region设为valueMatrix的值
            arguments (Input)
                this ImageWrapper
                matrixRange MatrixIndexRange
                valueMatrix (:,:) double
            end
            rowStart = matrixRange.rowStart;
            rowEnd = matrixRange.rowEnd;
            colStart = matrixRange.colStart;
            colEnd = matrixRange.colEnd;
            if ~isscalar(rowStart)
                fprintf("rowStart is Non scalar \n");
            end
            if ~isscalar(rowEnd)
                fprintf("rowEnd is Non scalar \n");
            end
            if ~isscalar(colStart)
                fprintf("colStart is Non scalar \n");
            end
            if ~isscalar(colEnd)
                fprintf("colEnd is Non scalar \n");
            end
%             fprintf("size of rowStart: \n");
%             disp(size(rowStart));
%             disp(class(rowStart));
%             fprintf("size of rowEnd: \n");
%             disp(size(rowEnd));
%             disp(class(rowEnd));
%             fprintf("size of colStart: \n");
%             disp(size(colStart));
%             disp(class(colStart));
%             fprintf("size of colEnd: \n");
%             disp(size(colEnd));
%             disp(class(colEnd));
%             fprintf("size of value matrix :\n");
%             disp(size(valueMatrix));
%             disp(class(valueMatrix));
            this.img(rowStart(1):rowEnd(1),colStart(1):colEnd(1)) = valueMatrix;
            this.flag_unset(rowStart(1):rowEnd(1),colStart(1):colEnd(1)) = 0;

        end

        function this = addAtMatrixRange(this,matrixRange,valueMatrix)
            arguments (Input)
                this ImageWrapper
                matrixRange MatrixIndexRange
                valueMatrix (:,:) double
            end
            rowStart = matrixRange.rowStart;
            rowEnd = matrixRange.rowEnd;
            colStart = matrixRange.colStart;
            colEnd = matrixRange.colEnd;

            this.img(rowStart:rowEnd,colStart:colEnd) = this.img(rowStart:rowEnd,colStart:colEnd) + valueMatrix;
            this.flag_unset(rowStart:rowEnd,colStart:colEnd) = 0;
        end

        function instance = extractSubImage(this,matrixRange)
            arguments (Input)
                this ImageWrapper
                matrixRange MatrixIndexRange
            end
            rowStart = matrixRange.rowStart;
            rowEnd = matrixRange.rowEnd;
            colStart = matrixRange.colStart;
            colEnd = matrixRange.colEnd;
            subImg = this.img(rowStart:rowEnd,colStart:colEnd);
            instance = ImageWrapper(subImg);
        end

        function fillUnsetPlacesWithValue(this,fillingValue)
            arguments (Input)
                this ImageWrapper
                fillingValue (1,1) double
            end
            this.img = this.img + this.flag_unset .* fillingValue;
        end

        function matrixRange = getFullMatrixRange(this)
            matrixRange = MatrixIndexRange(rowStart=1,rowEnd=this.imgShape.m_height,colStart=1,colEnd=this.imgShape.m_width);
        end

        function sz = shape(this)
            sz = [this.imgShape.m_height,this.imgShape.m_width];
        end

    end

    methods (Static)
        function instance = zeros(sz)
            arguments (Input)
                sz (1,2) 
            end
            instance = ImageWrapper(zeros(sz));

        end

        function instance = ones(sz)
            arguments (Input)
                sz (1,2)
            end
            instance = ImageWrapper(ones(sz));
        end

        
    end
end

[Raghu Boggavarapu]

Hi, This is a documented limitation for code generation: Handle Object Limitations for Code Generation - MATLAB & Simulink (mathworks.com) .

[zzm oliver]

Thanks for replying. I was aware of the doc, I just did not know how to write a workaround.

Answer 1

[Manoj Mirge]

The MATLAB coder must statically allocate memory for handle class objects, and allocating in a loop prevents static memory allocation. That is why the handle class objects cannot be allocated in the “for” loop. As you are allocating the handle class object “ImageWrapper” in the “for” loop, you are encountering this error.

Please refer to the attached MATLAB Answer link for a workaround to store the handle classes in cell array:

https://www.mathworks.com/matlabcentral/answers/1934804-why-does-the-memory-allocation-for-handle-class-objects-in-a-cell-array-cause-an-error-in-a-loop

Similarly, you can add the “setValue” method in the “ImageWrapper” handle class.

You can refer to below code for achieving the same:

classdef ImageWrapper < handle 
    properties 
        img (:,:) double  
        flag_unset (:,:) double  
        imgShape (1,1) ImgShape  
    end 
    methods 

        % Constructor method
        
        %The setValue method that again set the properties of the object.
        function this = setValue(this,img)  
            this.img = img; 
            this.flag_unset = ones(size(img)); 
            this.imgShape = ImgShape(size(img,2),size(img,1)); 
        end 
        
        % Other Mehods
    end 
end    

And in “stitch_spine” function you can use the “repmat” function to allocate the handle class in cell array and then later change the class value using the “setValue” method.

Please refer to below code to achieve the same:

intactImgs_list = repmat({ImageWrapper(imgStack_double(:,:,1))}, 1, numIntactImgs-1);  
for i=2:numIntactImgs 
  % Set the object as you would like. 
   setValue(Nodes{i}, imgStack_double(:,:,i) ); 
end 
    

Hope this helps.

[zzm oliver]

Great help, thanks!