Return values from figure callback

Hello,

I want to interactively choos datapoints from a graphic. The idea is to click on two datapoints which mark the start and the end of the region of interest. I came across this answer which was very helpful. Nevertheless, I'd like to implement this functionality in a function. How can I return the values from the callback?

In the main file, I'm generating the plot. Furhtermore, I'm calling the function to choose datapoints from the plot:

hFig = figure
plot(xx, yy);

xy = fchoose_from_plot(hFig) % call the function to choose datapoints from plot

The function looks as follows

function [xy] = fchoose_from_plot(hFig)
    
    % Start brushing mode and specify callback for when complete
    hBr = brush(hFig);
    hBr.ActionPostCallback = {@fonBrushAction,{'data'}};
    brush on
    
    % save selected datapoints
    xy = [];
    fprintf('select first ...\n');
    uiwait;
    xy = [xy, data'];
    fprintf('select second ...\n');
    uiwait;
    xy = [xy, data'];
    
    % turn off the brush and close figure
    hBr.Enable = 'off';
    close(hFig)

end

And the callback function is basically the same as in the linked post but I've tried to change 'base' to 'caller' in assignin.

% Callback for after the brush action has been completed
function fonBrushAction(~,eventdata,names)

    % Extract plotted graphics objects
    % Invert order because "Children" property is in reversed plotting order
    hLines = flipud(eventdata.Axes.Children);
    
    % Loop through each graphics object
    for k = 1:numel(hLines)
        % Check that the property is valid for that type of object
        % Also check if any points in that object are selected
        if isprop(hLines(k),'BrushData') && any(hLines(k).BrushData)
            % Output the selected data to the base workspace with assigned name
            ptsSelected = logical(hLines(k).BrushData.');
            data = [hLines(k).XData(ptsSelected).' ...
                hLines(k).YData(ptsSelected).'];
%             assignin('base',names{k},data)
            assignin('caller',names{k},data)
        end
    
        uiresume;
    end
end

Nevertheless, I get the error Unrecognized function or variable 'data' from where I can conclude, that the datapoints are not returned properly in the workspace of the function. How can I solve this issue?

[Stephen23]

"How can I return the values from the callback? "

Callbacks don't return arguments.

The standard ways of passing data around a GUI are explained here:

https://www.mathworks.com/help/matlab/creating_guis/share-data-among-callbacks.html

https://www.mathworks.com/help/matlab/creating_guis/share-data-across-callbacks-in-app-designer.html

Answer 1

[chrisw23]

I suggest to use the lines UserData property to save your data.

hLines(k).UserData = ...