[GUI] Update variable in while loop

Hello, I have problem with updating variable (handles.Background) in while loop when I press pushbutton. While loop:

 function CameraPreviewButton_Callback(hObject, eventdata, handles)
% hObject    handle to CameraPreviewButton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
 while get(hObject,'Value')
    img = im2double(handles.GigeCam.snapshot);
    data = (img(1,:) + img(2,:))/2;
    data = data - handles.Background;
    plot(handles.axes1,handles.CamVect,data);
    pause(0.1);
    drawnow;
 end
 guidata(hObject, handles);

Callback function:

 function SetBackButton_Callback(hObject, eventdata, handles)
 % hObject    handle to SetBackButton (see GCBO)
 % eventdata  reserved - to be defined in a future version of MATLAB
 % handles    structure with handles and user data (see GUIDATA)
 img = im2double(handles.GigeCam.snapshot);
 handles.Background = (img(1,:) + img(2,:))/2;
 guidata(hObject, handles);

It only works if I push tooggle button to stop while loop and then push again to start loop.

[OCDER]

I'm not quite understanding the setup here. You have 2 callbacks: CameraPreviewButton_Callback and SetBackButton_Callback.

When you push the CameraPreviewButton, there is NO call to the SetBackButton or handles.Background. So when exactly should handles.Background update within the while loop of CameraPreviewButton?

Answer 1

[Stephen23]

If you want any values of handles to change inside that loop because of something that you did in another callback then you will have to explicitly obtain handles again on each loop iteration:

while ...
    handles = guidata(hObject);
    ...
end

One copy of handles does is not shared between all callbacks: each time you change it within a callback it will create a copy local to that callback. It is only when you store that copy (using guidata) that it will be stored in the parent figure... and only then can you get the updated handles structure (either by triggering a callback, or calling handles=guidata(...)).

Or you could avoid this entire mess by writing your own GUI and using nested functions.