shengchan - I think what was missing from your code was the initialization of the contents variable...and so when you try to use it with
blocks = contents(get(hObject, 'Value'));
you probably get the Undefined function or variable 'contents'. Try doing
contents = cellstr(get(hObject, 'String'));
blocks = contents(get(hObject, 'Value'));
so that contents is defined before you use it.
