Tamfor - what is the process flow of your GUI? Does the user select some items in the listbox, and then presses the start1 button, and that takes the selected items and writes them to file? If so, then you should remove the cmp_list_Callback and put all that code/logic into the callback for start1.
function start1_Callback(hObject, eventdata, handles)
%other necessary data in between these lines
% get the selected items from the list box
index_selected = get(handles.cmp_list,'Value');
% create the materials list
Materials = {ABS,Aluminum,Cardboard,HIPS,KAOWOOL,Kydex,PEI,PET,PMMA,POM};
for i =1:size(index_selected,2)
RMAT(i)=(Materials(index_selected(i))); %Selected info we want to show
end
% save the selected items to file
FileName = uiputfile('*.cmp','Save as');
dlmwrite(FileName,RMAT,'');
Note how we use handles.cmp_list to get the handle of the listbox which we can then use to get the selected items.
A couple of questions - what are ABS, Aluminum, Cardboard, etc. Are they integers or strings or what? If strings, then are these the same strings that populate the list box? And if so, then rather than hard-coding that list here, why not just use
Materials = get(handles.cmp_list,'String');
which should return a cell array of those items in your list.
Also, what is the data type for RMAT?
