MATLAB slider value to data file

Question

I have the following MATLAB code:

function START_Callback(a,b)
global h;
global lastVal;
global picture1;
global picture2;
global nRep;
global MaxRep;
global index;
global files;
delete(gcf);

nRep = 1;
MaxRep = 529;

files = dir(fullfile('pictures','*.png'));
nFiles = numel(files);
combos = nchoosek(1:nFiles, 2);
index = combos(randperm(size(combos, 1)), :);
picture1 = files(index(nRep,1)).name;
picture2 = files(index(nRep,2)).name;
image1 = fullfile('pictures',picture1);
image2 = fullfile('pictures',picture2);
subplot(1,2,1); imshow(image1); title(picture1);
subplot(1,2,2); imshow(image2); title(picture2);

uicontrol('Style', 'text',...
        'Position', [200 45 200 20],...
        'String','How related are these pictures?');
uicontrol('Style', 'text',...
        'Position', [50 45 100 20],...
        'String','Unrelated');
uicontrol('Style', 'text',...
        'Position', [450 45 100 20],...
        'String','Closely related');
uicontrol('Style','pushbutton','String','Next Trial',...
        'Position', [250 350 100 20],...
        'Callback',{@NextTrial});

h = uicontrol(gcf,...
   'Style','slider',...
   'Min' ,0,'Max',50, ...
   'Position',[100 20 400 20], ...
   'Value', 25,...
   'SliderStep',[0.02 0.1], ...
   'BackgroundColor',[0.8,0.8,0.8]);

set(gcf, 'WindowButtonMotionFcn', @cb);

lastVal = get(h, 'Value'); 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function cb(s,e)
global h
global lastVal;
global picture1;
global picture2;
global fileout;
global SaveResults;

fid = fopen(fileout, 'a');
    if get(h, 'Value') ~= lastVal;
        lastVal = get(h, 'Value');
        if SaveResults > 0;
        fprintf(fid, '%s\t%s\t%f\n', picture1, picture2, lastVal);
        fclose(fid);
        else
        fclose(fid);
    end
end

My problem is with the way lastVal is saved in the datafile. The problem is twofold:

1. If the slider isn't moved, no value is saved. So if it is left in the starting position (25), and "Next Trial" is clicked, it ignores that trial as if it hadn't happened. I don't want this. I want it to save whatever the value of the slider position is, regardless of whether it was moved or not.

2. The datafile looks like this:

   monkey.png  ostrich.png 24.262537
   monkey.png  ostrich.png 23.082596
   monkey.png  ostrich.png 20.870207
   monkey.png  ostrich.png 17.772862
   monkey.png  ostrich.png 13.790561
   monkey.png  ostrich.png 9.218289
   monkey.png  ostrich.png 5.383481
   monkey.png  ostrich.png 3.023599
   monkey.png  ostrich.png 2.433628
   

That is, MATLAB isn't just saving the LAST position of the slider when it is moved, it is saving all intermediate values as well. So I want the above to only be:

monkey.png  ostrich.png     2.433628

How do I get it to ONLY print the last position of the slider at the end of the trial (including the default value if the slider is not moved)?

Answer 1

Put the file writing code in the button callback (@NextTrial) not the slider callback (@cb).