MATLAB: How to add new imroi objects to an array

Image Processing Toolboximroi

At the moment, I am creating new imroi objects manually like so:

line1 = imline(main_axes, [1 2], [1 2], ...
                        'PositionConstraintFcn', constraint_line);
line2 = imline(main_axes, [2 3], [2 3], ...
                        'PositionConstraintFcn', constraint_line);
line3 = imline(main_axes, [3 4], [3 4], ...
                        'PositionConstraintFcn', constraint_line);

However, what I really want is to store the imroi objects in an array. Something a bit like this:

line_objects(line1, line2, line3)

Then my objective is to use this to add line objects from the press of a button like so:

line_button = uicontrol('style', 'pushbutton',...
                  'string', 'Add a line', ...
                  'callback', {@add_line, line_objects});

Can anyone give some general advice on how to approach this?

Best Answer

My understanding is that you would like to use the "line_objects" variable across callbacks in your GUI. Rather than trying to pass a "line_objects" variable around as an argument to "add_line", I suggest sharing the variable using "setappdata"/"getappdata" or "guidata". The following link provides an overview of different approaches for sharing data in GUIs as well as examples: http://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

Related Solutions

MATLAB: How to add a new element to an object array using pass by reference

The documentation on Initialize Arrays of Handle Objects says "[...] Creates unique handles for each element in the array." I assume that explains the behaviour you see.

Another potential solution: Preallocate a large enough array. It doesn't require that much memory. And implement a mechamism to keeps track of the "current size" of the arryay. MWE:

>> object_array(1,12) = MyClass(-1);
>> add_MyClass_object( object_array )
>> add_MyClass_object( object_array )
>> add_MyClass_object( object_array )
>> [object_array.ID]
ans =
     1     2     3    -1    -1    -1    -1    -1    -1    -1    -1    -1
>>

where

classdef MyClass < handle
    properties
        ID
    end
    methods
        function this = MyClass( id )
            if nargin == 0
                this.ID = -1;
            else
                this.ID = id;
            end
        end
    end
end

and

function  add_MyClass_object( array )
    nxt = find( [array.ID] == -1, 1, 'first' );
    array(1,nxt).ID = nxt; %#ok<*NASGU>
end

Your "awfully clunky" approach is that something like this?

>> ac = ArrayContainer;
>> ac.add_object
>> ac.add_object
>> ac.add_object
>> [ac.object_array.ID]
ans =
     1     2     3

where

classdef    ArrayContainer < handle
    properties
        object_array (1,:)  MyClass   = MyClass.empty
    end
    methods
        function    add_object( this )
            len = numel(this.object_array);
            this.object_array(1,end+1) = MyClass(len+1);
        end
    end
end

Comment: When using approaches like these in real applications one will certainly encounter problems, which one didn't anticipate up front. Experiments are needed, e.g.

>> ac.object_array(2).ID = 200;
>> [ac.object_array.ID]
ans =
    -1   200
>>

:-( What *** happened? )-:

Guess what this returns

%%

object_array(1,12) = MyClass(-1);
add_MyClass_object( object_array )
add_MyClass_object( object_array )
add_MyClass_object( object_array )
[object_array.ID] %#ok<*NOPTS>

%%
object_array(1,2).ID = 200;
[object_array.ID] %#ok<*NOPTS>

Conclusion: Don't try to outsmart Matlab!

/R2018b

MATLAB: How to display an array in uitable GUI when click “show table” button

1. 'ColumnFormat' needs to be a cell array, so use

h = uitable('Data', dat, 'ColumnFormat', {'numeric'});

2. It looks to me you already have a uitable in your GUI, why do you create another uitable? I think you should do:

set(handles.uitable_data, 'Visible', 'on');
set(handles.uitable_data, 'Data',dat, 'ColumnFormat',{'numeric'});

Best Answer

Related Solutions

MATLAB: How to add a new element to an object array using pass by reference

MATLAB: How to display an array in uitable GUI when click “show table” button

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