Hi Laurensius,
My understanding from the question is that you would like to perform different action when the popup list element is chosen for the first time than when the list element is chosen for the second time.
We can use 'persistent' variable for this purpose which holds the value between the function calls (Similar to 'static' variable in C). Based on the value of the persistent variable you may take different action as per required.
As an illustration, you may consider the following code in the callback of the particular popup:
b=valueOfPersistent;
if(b==1)
% the add_line and add_block code
disp('b==1');
else
%Code to delete the old add_line and _block and add new add_line and _block
disp(b);
end
And write the function 'valueOfPersistent' as follow:
function b=valueOfPersistent
persistent a;
if isempty(a)
a=1;
end
b=a;
a=a+1;
end
Here the function initializes the variable 'a' only once and increment the values each time the function is called from the callback and returns the latest value.
