Function inside GUI don't save modifies to "handles"

Hi everybody, I'm trying to do my first GUI, but I'm having some problems. Excuse me if my question is a bit stupid.

When I call a function (located inside the same .m file of the main code) I'm not able to modify the handles structure from inside the function.

I've done a very easy code to explain it better:

function pushbutton1_Callback(hObject, eventdata, handles)

      handles.A=1;
      guidata(hObject, handles);

      modify_A(hObject, eventdata, handles)

      disp(num2str(handles.A))

%%%%%%%%%%%%

function modify_A(hObject, eventdata, handles)

      handles.A=100;
      guidata(hObject, handles);

How can i do it?

thank you very much.

[Jose abel De la Fuente]

Hi.

I have one problem seemed, which does not allow me update the handles.

My problem start when I try using the uipushtool and the ClickedCallback. In the handle function I have tried to update the handle of this way:

 uipushtool(tbh,'CData',imread('Complementos\Verde.png'),'Separator','off',...
                          'TooltipString','Your toggle tool',...
                          'HandleVisibility','off',...
                          'ClickedCallback',...
                              {@marcarPunto,handles, cmP,cnP}); 

function marcarPunto(hObject,event,handles,cmP,cnP) 
     [handles.pnSin(cnP,cmP),handles.pmSin(cnP,cmP)]=ginputc(1, 'Color', 'w');    
     guidata(hObject,handles);

Please I will grateful with someone who could help me.

In my example hanldes has two elements (pnSin and pmSin).

[Walter Roberson]

Jose abel De la Fuente: you are writing the x and y outputs of ginputc to the same output location. The location is going to end up as just the y value.

Answer 1

[Jan]

function pushbutton1_Callback(hObject, eventdata, handles)
    handles.A = 1;
    guidata(hObject, handles);   % Store handles
    modify_A(hObject, eventdata, handles)  % Update handles
    handles = guidata(hObject);  % Get newest version of handles
    disp(num2str(handles.A))

%%%%%%%%%%%%
function modify_A(hObject, eventdata, handles)
    handles.A = 100;  % modify handles
    guidata(hObject, handles);  % Store updated handles

Or more direct:

function pushbutton1_Callback(hObject, eventdata, handles)
    handles   = guidata(hObject);  % Do not trust handles from input
    handles.A = 1;
    handles   = modify_A(hObject, eventdata, handles)  % Update handles
    disp(num2str(handles.A))

%%%%%%%%%%%%
function handles = modify_A(hObject, eventdata, handles)
    handles.A = 100;  % modify handles

[Luca Amerio]

Great, I tried the second version and it works very well. Just one question: what it means:

handles   = guidata(hObject);  % Do not trust handles from input

It seams to works also without it, but i can't understand what it is. Why i shouldn't trust the handles variable from the input? What is the difference between that one and

guidata(hObject, handles);  % Store updated handles

?

My incomprehension could come from the fact that I don't really know what handles and hObject are, in addition to how this kind of function (without output) really work. Can you suggest me a place where I can find a more detailed description of this stuffs?

Thank you anyway very much for your help

[Jan]

The "handles" from the input arguments are the version of the struct during the creation of the figure. Therefore later changes of this struct might not be included. If you do not modify this variable or GUIDE updates it, there is no problem. But this migtht depend on the GUIDE version, therefore it is a good idea to get the current version of handles manually.

"handles" is simply a struct here. The name is misleading, because it can contain anything and not only handles. A handle is a kind of unique address for each GUI element.

While "handles = guidata(hObject)" reads the struct from the figure's application data, "guidata(hObject, handles)" writes the struct back. Inside the command guidata thuis happens:

% handles = guidata(hObject)
set(ancestor(hObject, 'figure'), 'ApplicationData', handles);

% guidata(hObject, handles)
handles = get(ancestor(hObject, 'figure'), 'ApplicationData');

For clarity I leave out, that guidata uses a field of the ApplicationData only.

Answer 2

[Jing]

That's because you didn't update A after modification! Before disp, you should get A back from the handles by "A=handles.A;".

[Luca Amerio]

I'm very sorry. The dummy code I showed you is wrong. The error is given with disp(num2str(handles.A)) It happens even if i add a guidata(...) after the modify_A call.

[Jan]

Please do not post wrong code and mention this in a comment to an answer. Use the chance to edit the original question, because this would be less confusing for the readers. And when you want the assistence of voluntary helpers, any kind of confusion is a bad idea.

[Luca Amerio]

I repeat: i'm very sorry. I tested the dummy code before posting it, but then i decided to modify it a little bit to make it clearer. I didn't noticed that i forgot to modify that value.

I try to be as clear and precise I can when I ask for help, but sometimes I miss something.

Sorry