Is it possible to pass a variable throu a callback function?

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Merse Gaspar 2023-5-28

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https://ww2.mathworks.cn/matlabcentral/answers/1974694-is-it-possible-to-pass-a-variable-throu-a-callback-function

评论： Walter Roberson 2023-5-28

My problem is, that I have lots off similar buttons, generated inside a for cycle, and I dont want to write the same number of callback functions. It would suffice if a parameter could be passed to indicate which button is called, i.e. which button calls the function. Example:

for i = 1:100
    mybutton(i) = uicontrol('Style','pushbutton','String',sprintf('Nr. %d',i),'Position',[30*i,10,20,20],'BackgroundColor',[.5 .5 .5],'Callback',{@button_Callback});
end

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Answer 1

Walter Roberson 2023-5-28

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Yes. In general see http://www.mathworks.com/help/matlab/math/parameterizing-functions.html

However, in the special case of setting up callbacks, when you use the cell syntax like you do in 'Callback',{@button_Callback} then anything you put as additional cell elements will be passed as an additional parameter to the function. So for example if you had 'Callback', {@button_Callback, i} then the value of i as of the time the control is built, would be passed as the third parameter to button_Callback so you could know the button number.

However... even that turns out to be unnecessary. When a callback is invoked, the first thing passed to the callback is the handle to the object that the callback is about. So even with just 'Callback',{@button_Callback} the first parameter passed to button_Callback would be the handle to the uicontrol, same as what would have been stored into mybutton(i) . You can use that to access the uicontrol properties, including the String property, or including any UserData that you might have set when you built the uicontrol.

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Merse Gaspar 2023-5-28

Thank you very much, this {@button_Callback, i} looks very nice and simple, but how can I extract the value i in the Callback function. How to refer the cell?

Walter Roberson 2023-5-28

在 MATLAB Online 中打开

You would declare

function button_Callback(hObject, event, button_number)

and access button_number inside the callback.

As I indicate though, you do not need to do this as you can access hObject.String or hObject.UserData. For example,

for i = 1:100
    mybutton(i) = uicontrol('Style', 'pushbutton', ...
                            'String', sprintf('Nr. %d',i), ...
                            'Position', [30*i,10,20,20], ...
                            'BackgroundColor', [.5 .5 .5], ...
                            'Callback',@button_Callback, ...
                            'UserData', i);
end