MATLAB: Error starting a GUI

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I have developed a simple gui with radiobuttons. Everything works fine as long as I start the gui from the script and then use it. If I start directly the gui.fig file, I got this rerror message when I start using the GUI:

Struct contents reference from a non-struct array object.
Error in gui>pushbutton1_Callback (line 88)
    dataSet = get(handles.errorset_groupbutton.SelectedObject,{'String','Value'})
Error in gui_mainfcn (line 95)
        feval(varargin{:});
Error in gui (line 42)
    gui_mainfcn(gui_State, varargin{:});
Error in
matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)gui('pushbutton1_Callback',hObject,eventdata,guidata(hObject)) 
Error while evaluating UIControl Callback.

Best Answer

That .fig file is not the complete GUI, it is only the visible elements. The callback functions it references are not contained in the figure, so when you try to execute a function, that function can't work properly, because the guidata wasn't set correctly.

You have already identified the solution: don't start the GUI by opening the fig, but start it with the function. If you can't keep them apart, don't use a fig, but either click the 'generate code' option in GUIDE, or avoid GUIDE in the first place.

If you want some hints about avoiding GUIDE, I'dd be happy to give you some pointers about what I do (or you can just have a look at my FEX submission to see some examples).

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MATLAB: GUI – Once working codes doesn’t work now with ‘Struct contents reference from a non-struct array object’ error

The posted code works for me in R2016b, provided that I run the .m (you cannot run by double-clicking on the fig)

MATLAB: Attempt to reference field of non-structure array

Each handles structure is associated with a particular figure. When you are using GUIDE, the handles structure that would be automatically referenced on your behalf would belong to the figure (GUI) that the graphics object is part of. That handles structure is not going to know anything about the handles structure of the other figure (GUI) unless you specifically passed in that information.

When the first GUI calls upon the second GUI, the figure handle of the second GUI will be returned to the caller in the first GUI. The first GUI can then use guidata() on the second figure's figure handle in order to get the second GUI's handles, and the first GUI can then write the first GUI's figure handle into the second GUI's handles. Then in the second GUI, when something is needed out of the first GUI, that recorded figure handle can be used to retrieve the first GUI's handles. For example,

%in first gui
fig1 = gcf();          %first GUI's figure handle
fig2 = SecondGUI();    %returns second GUI's figure handle
handles2 = guidata(fig2);   %fetch second GUI's handles
handles2.fig1 = fig1;       %record first GUI's figure handle
guidata(fig2, handles2);    %and update second GUI's handles

and in second GUI

function some_callback(hObject, event, handles)
  %in second GUI, handles refers to handles for second GUI
  %and we stored a copy of the first GUI's figure handle there
  fig1 = handles.fig1;
  handles1 = guidata(fig1);     %retrieve handles for first GUI
  get(handles1.T, 'String')     %reference to something in first GUI

Alternately, in the case where there is only one object with the tag T, you can skip all of this and instead use

   function some_callback(hObject, event, handles)
     T = findall(0, 'Tag', 'T');    %come out come out where-ever you are!
     get(T, 'String')

findall can search all objects in all figures. It is not as efficient as the code from above, and you have complications if there are multiple objects with the same Tag.

Best Answer

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MATLAB: GUI – Once working codes doesn’t work now with ‘Struct contents reference from a non-struct array object’ error

MATLAB: Attempt to reference field of non-structure array

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