Use addNewPositionCallback to updates stored line coordinates in GUIDE

Hello all,

I have read everything I could about the use of Callbacks in GUIDE, but I may use a little help from experienced users. I am trying to update a handles every time I resize an imline line, so I can use their coordinates later in my program. I cannot find the correct way to word it in Matlab. Here is an extract of the code:

handles.h = imline(gca,[-1 -1],[-2 2]);
id = addNewPositionCallback(handles.h,@hpos); 
% Update handles structure
guidata(hObject, handles);

 function hpos(h,handles)
% Display image info
set(handles.iminfo, 'String',{['It works!']});

I get the following error message: "Error while evaluating Figure WindowButtonMotionFcn.

Not enough input arguments."

Anybody could guide me in the right direction? Thanks in advance!

Answer 1

[Greg]

From the documentation:

addNewPositionCallback — Add new-position callback to ROI object
id = addNewPositionCallback(h,fcn) adds the function handle fcn to the list of new-position callback functions of the ROI object h. Whenever the ROI object changes its position each function in the list is called with the syntax:
fcn(pos)
where pos is of the form returned by the object's getPosition method.
The return value, id, is used only with removeNewPositionCallback.

This indicates that only 1 input is being passed to hpos, and you've define it to require 2 inputs. I'm not sure it'll work, but I would try:

handles.h = imline(gca,[-1 -1],[-2 2]);
id = addNewPositionCallback(handles.h,{@hpos,handles.iminfo}); 
% Update handles structure
guidata(hObject, handles);

   function hpos(pos,iminfo_obj)
   % Display image info
   set(iminfo_obj, 'String','It works!');
   % I'm assuming 'It works!' is a placeholder and you want to use pos above

[Farbos de Luzan]

Thank you very much Greg for this quick answer. Indeed the "It Works!" was supposed to be a placeholder (I wanted to keep it simple for a start). Your post actually helped me understanding how to specify the inputs to my callback function. Then I had another error message that I could fix thanks to this post:

https://www.mathworks.com/matlabcentral/answers/2032-problem-with-drawing-multiple-rois-on-an-image-using-imfreehand-with-ability-to-perform-post-process?s_tid=answers_rc1-2_p2_MLT

[Greg]

Glad it worked out.