How do I add new imroi objects to an array?

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?

Answer 1

[Rebecca Krosnick]

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

[Hasan Aslam]

Hey, thanks for the reply. I actually posted this a while ago now and I managed to think of a way using the button UserData attribute (which I think is similar to the guidata you mentioned). Here is my solution in case anybody wishes to use it in the future.

I used a cell array to store created object handles, then I stored this array in the 'UserData' attribute of the button. This is all done inside the button callback:

 if isempty(get(object_handle, 'UserData'))

    % If the array doesn't exist, create it

    object_array = cell(10, 1);
    set(object_handle, 'UserData', imroi_array);

 end

 % Retrieve the array from the 'UserData' property

 object_array = get(object_handle, 'UserData');

Then I found this handy function online to find the next empty cell (Source: http://stackoverflow.com/questions/3400515/how-do-i-detect-empty-cells-in-a-cell-array)

% Find the next empty cell to store our imroi object

next_cell = find(cellfun(@isempty, object_array),1);
object_array{next_cell} = imline(gca, [3 4], [3 4], ...
                      'PositionConstraintFcn', constraint);

And finally, update the user_data again:

 % Update the UserData attribute 
 set(object_handle, 'UserData', imroi_array);

Oh, and it doesn't handle deleted objects yet. You can easily do so by checking at the start of the callback if any of the objects have been deleted using isvalid(handle), and set the cell array index to {}.