Trying to Program a Switch-Case Expression for a Pop-up Menu in a MATLAB GUI

Can someone tell me what's wrong with my syntax or any other errors you spot?

% --- Executes on selection change in popupmenu_filters.
function popupmenu_filters_Callback(hObject, eventdata, handles)
% hObject    handle to popupmenu_filters (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% determine which filter to apply by reading string in pop-up menu
str = get(hObject, 'String');
val = get(hObject, 'Value');

% set current filter to the user-selected filter
switch str{val};
    case 'imdilate' 
        handles.current_filter = imdilate
    case 'imerode'
        handles.current_filter = imerode
    case 'imopen'
        handles.current_filter = imopen
    case 'imclose'
        handles.current_filter = imclose
    case 'imtophat'
        handles.current_filter = imtophat
    case 'imbothat'
        handles.current_filter = imbothat
    case 'entropy filter'
        handles.current_filter = entropyfilt
end

handles.image2 = handles.current_filter(handles.image);
  handles.axes2(imshow(handles.image2));
  % pushbutton_save handles structure
  guidata(hObject, handles);

Answer 1

handles.current_filter = @imdilate;

Without the @ it is going to _ call_ imdilate with no arguments.

Answer 2

So when I'm adding slider capability to the code, how do I call that within the program. Would it be:

handles.image2 = handles.current_filter(handles.image, [handles.slider1 handles.slider2]; 

or something like that?

And I'm still getting error messages like...

Error using iptchecknargin (line 57)
Function IMDILATE expected at least 2 input arguments
but was called instead with 0 input arguments.

Error in imdilate (line 119)
iptchecknargin(2,4,nargin,mfilename);

Error in FESgui>popupmenu_filters_Callback (line 544)
        handles.current_filter = @imdilate

Error in gui_mainfcn (line 96)
        feval(varargin{:});

Error in FESgui (line 49)
    gui_mainfcn(gui_State, varargin{:});

Error in @(hObject,eventdata)FESgui('popupmenu_filters_Callback',hObject,eventdata,guidata(hObject))

Error using waitfor
Error while evaluating uicontrol Callback

because it's not recognizing my input arguments. What is causing that issue?

What input arguments? You aren't passing any input arguments?

But @imdilate should only be creating a function handle, not calling imdilate.

What happens if you type

@imdilate

at the command prompt?

Wait... just how old is your MATLAB?

I'm using R2011b

And using the @function_handle has worked so far. I just haven't been able to apply the changes from the slider to the function.

Answer 3

Rather than using switch I would package this as a cell array of function handles and then extract the value:

ops={@imdilate,@imerode,@imopen} %etc
handles.current_filter = ops{val};

This still works for a pop-up menu? How does the program know what the user selected?

Your code had

val = get(hObject, 'Value');

so Sean used that.

Just make sure your ops structure is in the same order as the entries in your String property.

Now it's giving me this error:

Attempted to access handles.axes2(234.013); index must be a positive integer or logical.

Error in FESgui>popupmenu_filters_Callback (line 562)
handles.axes2(imshow(handles.image2));

Even though my handles structure contains handles for axes2

            pushbutton_browse: 238.0118
                        axes2: 233.0125
                        axes1: 228.0066
                     uipanel5: 243.0062
                     uipanel4: 241.0061
                     uipanel3: 239.0079
                     uipanel2: 56.0078

It should just be:

imshow(handles.image2,'parent',handles.axes2);