MATLAB GUI using GUIDE: List Box problem

Question

I'm creating a MATLAB GUI that contains two uicontrol objects: a pushbutton and a listbox. I use the pushbutton to add file names to the listbox. When I run the GUI from the m-file it works fine. The problem occurs only when I run the .fig file itself. Here is the callback code and the error:

function add_file_Callback(hObject, eventdata, handles)
% hObject    handle to add_file (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
%gets input file(s) from user

[input_file,pathname] = uigetfile( ...
       {'*.jpg;*.tif;*.png;*.gif;*.bmp;*.pgm'}, ...
        'Select files', ... 
        'MultiSelect', 'on');

%if file selection is cancelled, pathname should be zero
%and nothing should happen
if pathname == 0
    return
end

%gets the current data file names inside the listbox

inputFileNames = get(handles.img_list,'String');

%if they only select one file, then the data will not be a cell
%if more than one file selected at once,
%then the data is stored inside a cell
if iscell(input_file) == 0

    %add the most recent data file selected to the cell containing
    %all the data file names
    inputFileNames{end+1} = input_file;

%else, data will be in cell format
else
    %stores full file path into inputFileNames
    for n = 1:length(input_file)
        %notice the use of {}, because we are dealing with a cell here!
        inputFileNames{end+1} = input_file{n};
    end
end

%updates the gui to display all filenames in the listbox
set(handles.img_list,'String',inputFileNames);

%make sure first file is always selected so it doesn't go out of range
%the GUI will break if this value is out of range
set(handles.img_list,'Value',1);

% Update handles structure
guidata(hObject, handles);

Error:

Error in ==> Texture_Classification_GUI>add_file_Callback at 154
inputFileNames = get(handles.img_list,'String');

Error in ==> gui_mainfcn at 95
        feval(varargin{:});

Error in ==> Texture_Classification_GUI at 42
    gui_mainfcn(gui_State, varargin{:});

??? Error using ==> Texture_Classification_GUI('add_file_Callback',gcbo,[],guidata(gcbo))
Attempt to reference field of non-structure array.

??? Error while evaluating uicontrol Callback

Any help would be much appreciated.

Answer 1

Hmmm, what do you mean by "running the fig file itself"? GUIDE creates two files: an m-file and a .fig file (for example my_guide_app.m and my_guide_app.fig). Are you opening the .fig with something like openfig? This won't work because the m-file needs to set the figures opening function which creates the handle structure. So to run GUI's made with GUIDE it is necessary to call the m-file to launch the application and not just open the .fig file.

Let me know if I misinterpreted your statement about opening the .fig file, because there could be something else wrong.

Answer 2

Listbox needs to be initialized in the GUIDE I guess. If you initialize it with 1 option, it will be a char array, if you initialize it with more than 1 option, it will be a cell array. So, you have to put a similar check there (iscell) as well; and then add the new options.