MATLAB: Creating a timer in GUI

Question

Hi I'm using GUI for do a spectrum analyzer interface. My problem is when I create a timer and call my function, appears a warning, something like that:

"the "handles" estructure is no defined or recognized"

thi is a part of my code:

% --- Executes on button press in pushbutton4.
function pushbutton4_Callback(hObject, eventdata, handles)
obj1 = instrfind('Type', 'gpib', 'BoardIndex', 0, 'PrimaryAddress', 18, 'Tag', '');
if isempty(obj1)
    obj1 = gpib('ni', 0, 18);
else
    fclose(obj1);
    delete(obj1);
    clear obj1;
    obj1 = gpib('ni', 0, 18);
end
% Configure instrument object, obj1.
set(obj1, 'InputBufferSize', 10000);
set(obj1, 'OutputBufferSize', 10000);
% Connect to instrument object, obj1.
set(obj1,'Timeout',5);
fopen(obj1);
Nombre = query(obj1, '*IDN?');
set(handles.text1,'String',Nombre);
fprintf(obj1,':FORM:BORD SWAP');
fprintf(obj1,':FORM:DATA REAL,32');
% Get the nr of trace points
nr_points = str2double(query(obj1,':SWE:POIN?'));
% Get the reference level
ref_lev = str2num(query(obj1,':DISP:WIND:TRAC:Y:RLEV?'));
% Put the instrument in continuos mode
fprintf(obj1,':INIT:CONT ON');
% Create and bring to front fi gure number 1
%figure(1)
% Create a plot handle, ph, and draw a line at the refl evel
handles.axes1=(1:nr_points);
ph = plot(handles.axes1,ref_lev*ones(1,nr_points));
% Adjust the x limits to the nr of points
% and the y limits for 100 dB of dynamic range
xlim([1 nr_points])
ylim([ref_lev-100 ref_lev])
% Activate the grid
grid on
t =timer('timerfcn',@graficar,'Period',0.1);  //THIS IS MY TIMER
handles.varobj1=obj1;
handles.varph=ph;
start(t);
guidata(hObject,handles);
% hObject    handle to pushbutton4 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
    function graficar(hObject, eventdata, handles) //THIS IS MYFUNCTION
    obj1=handles.varobj1; //THE WARNING REFERS TO THIS 
    ph=handles.varph;     //LINE OF CODE
    fprintf(obj1,':TRAC? TRACE1');
    data = binblockread(obj1,'float32');
    fscanf(obj1); %removes the terminator character
    % Change the plot line data (fast update method)
    set(ph,'Ydata',data);
    % fl ushes the plot event queue
    drawnow
    guidata(hObject,handles);

Answer 1

t  = timer('timerfcn', {@graficar, gcf},'Period',0.1);

and

   function graficar(hObject, eventdata, fignum)
      handles = guidata(fignum);