Why won't my GUI code work!?

I have built a GUI using GUIDE. I have a lot of handles so have only included the code of the call back functions for one of each handle type here: c_callback (edit text box), c_slider_callback(slider), c_unit_callback(drop down menu), and calculate.callback(push button):

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function c_Callback(hObject, eventdata, handles)

% Obtain the new c value entered in the box
NewVal = str2double(get(hObject,'String'));
%  If there is no value or it is outwith limits, restore to the previous value from the slider
if  isempty(NewVal) || (NewVal<get(handles.c_slider,'Min')) || (NewVal>get(handles.c_slider,'Max'))
    set(hObject,'String',get(handles.c_slider,'Value'));
    %  Otherwise the value is correct so change the slider value
else
    set(handles.c_slider,'Value',NewVal)
end

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% --- Executes on button press in calculate.
function Calculate_Callback(hObject, eventdata, handles)

c_unit_Callback(hObject, eventdata, handles)
h_0_unit_Callback(hObject, eventdata, handles)
omega_unit_Callback(hObject, eventdata, handles)
r_0_unit_Callback(hObject, eventdata, handles)
F_unit_Callback(hObject, eventdata, handles)

n_p   = (get(handles.n_p_slider,  'value'));
c     = (get(handles.c_slider,    'value'))*c_unit;
nu    = (get(handles.nu_slider,   'value'));
h_0   = (get(handles.h_0_slider,  'value'))*h_0_unit;
omega = (get(handles.omega_slider,'value'))*omega_unit;
r_0   = (get(handles.r_0_slider,  'value'))*r_0_unit;
F     = (get(handles.F_slider,    'value'))*F_unit;
n     = (get(handles.n_slider,    'value'));

% THIS IS JUST CODE FOR CALCULATIONS. NOT IMPORTANT:

theta = (0.8*360/n_p)*pi/180;
r = r_0;
F_max = 0;
while F_max < F;
    r = r + 10E-3; % increase radius by 1 mm
    U = r*omega; % calculate tangential velocity U at radius r
    L = r*theta; % calculate arc length L at radius r
    x = linspace(0,L,n+1);
    delta_x = L/n;
    h = h_0 + x*tan(c);
    p = zeros(1,n+1);
    p_max_old = 0; p_max_new = 1;
    while abs(p_max_new-p_max_old)>(0.001E-2*p_max_new)
        p_max_old=p_max_new;
        for i=2:n
            p(1,(i)) = (p(1,(i+1)) + p(1,(i-1)))/2 ...
                + (3*c*(p(1,(i+1)) - p(1,(i-1))) * delta_x)./(4*h(1,i))...
                + (3*nu*U*c*delta_x^2)./h(1,i).^3;
        end
        p_max_new=max(p);
    end
    p_mean = mean(p);
    A = pi*(r^2-r_0^2)*theta/(2*pi); % find area of pad
    F = p_mean*A; % find maximum force
end

% END OF CALCULATIONS. IMPORTANT:

% display the results in the text boxes
set(handles.P_max,'string',num2str(p_max_new));
set(handles.A,'string',num2str(A));
set(handles.D,'string',num2str(2*r));

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% --- Executes on selection change in c_unit.
function c_unit_Callback(hObject, eventdata, handles)

% retrieve unit selection from drop down list

str = get(hObject, 'String');       %  Obtain the pop up selection string
val = get(hObject, 'Value');        %  Obtain the pop up selection value
switch str{val};
    case 'mrad'       %  If the choice is mrad set c_unit to 1E-3
        c_unit=1E-3;
    case 'rad'        %  If the choice is rad set c_unit to 1
        c_unit=1;
    case 'deg'        %  If the choice is rad set c_unit to pi/180
        c_unit=pi/180;
end

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% --- Executes on slider movement.
function c_slider_Callback(hObject, eventdata, handles)

% Put the current slider value in the corresponding text box
set(handles.c,'String',num2str(get(hObject,'Value')));

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When I run the code the GUI appears. When I click the calculate button the following error appears:

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??? Cell contents reference from a non-cell array object.

Error in ==> GUI>c_unit_Callback at 454
switch str{val};

Error in ==> GUI>Calculate_Callback at 305
c_unit_Callback(hObject, eventdata, handles)

Error in ==> gui_mainfcn at 96
        feval(varargin{:});

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

Error in ==> @(hObject,eventdata)GUI('Calculate_Callback',hObject,eventdata,guidata(hObject))

??? Error while evaluating uicontrol Callback

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Line 454 is: switch str{val};

Any help is much appreciated. Thanks

Answer 1

[Matt Fig]

What is in the popup menu? To see this, take the semicolon off of the line where you retrieve the string, like this:

str = get(hObject, 'String')%  Obtain the pop up selection string

Then when you run the GUI and select something from that popup, show us what prints out to the screen.

[Matt Fig]

Grand comments:

Thanks for the reply. I defined the popup menu with the string field in the property editor of GUIDE. Following your instructions, the command window shows str =

      'mrad'
      'rad'
      'deg'
Hopefully this helps you work out my problem

Answer 2

[Jan]

Please set a breakpoint in the line 454 "switch str{val}". Then run the program until it stops there. Now check the type and size of "str".

Another method to debug is:

dbstop if error

Then the program stops, if the error occurs. Then the variable "str" can be checked again. I guess, that the callback function is called from another function also, which replies a string instead of a cell string.

[Matt Fig]

Grant comments

Okay,

setting the breakpoint and running the program to there, str is: >> str ??? Undefined function or variable 'str'.

Then typing dbstop if error into the command window and checking str:

K>> str

str =

Calculate

str shouldn't be Calculate, it should be: 'mrad' 'rad' 'deg'

Any idea where the problem lies? I'll search for it in the meantime

Answer 3

[Nick]

by using:

str = get(hObject, 'String');

You call the name/ tag of the popupmenu and not the string that is inside the popupmenu. From the comment you gave on Jan Simon I gess the Tag you assigned to your popupmenu is Calculate. If this is true I would surgest the following code:

handles = guidata(gcbo);

str   = get(handles.Calculate, 'String'); 
  %str now contains all strings from the popupmenu

val = get(handles.Calculate,'Value');
  %the value now is the selected value from the popupmenu

    switch str(val)
    %etc