GUI Interface Arduino Error

Hi I am new in the arduino/matlab interface and I am having a problem.My GUI is a simple 2 button On/Off This is my code:

    function varargout = untitled2(varargin)
    % UNTITLED2 MATLAB code for untitled2.fig
    %      UNTITLED2, by itself, creates a new UNTITLED2 or raises the existing
    %      singleton*.
    %

      if true
        % code
      end
    %      H = UNTITLED2 returns the handle to a new UNTITLED2 or the handle to
    %      the existing singleton*.
    %
    %      UNTITLED2('CALLBACK',hObject,eventData,handles,...) calls the local
    %      function named CALLBACK in UNTITLED2.M with the given input arguments.
    %
    %      UNTITLED2('Property','Value',...) creates a new UNTITLED2 or raises the
    %      existing singleton*.  Starting from the left, property value pairs are
    %      applied to the GUI before untitled2_OpeningFcn gets called.  An
    %      unrecognized property name or invalid value makes property application
    %      stop.  All inputs are passed to untitled2_OpeningFcn via varargin.
    %
    %      *See GUI Options on GUIDE's Tools menu.  Choose "GUI allows only one
    %      instance to run (singleton)".
    %
    % See also: GUIDE, GUIDATA, GUIHANDLES

    % Edit the above text to modify the response to help untitled2

    % Last Modified by GUIDE v2.5 13-Nov-2015 15:22:51

    % Begin initialization code - DO NOT EDIT
    gui_Singleton = 1;
    gui_State = struct('gui_Name',       mfilename, ...
                       'gui_Singleton',  gui_Singleton, ...
                       'gui_OpeningFcn', @untitled2_OpeningFcn, ...
                       'gui_OutputFcn',  @untitled2_OutputFcn, ...
                       'gui_LayoutFcn',  [] , ...
                       'gui_Callback',   []);
    if nargin && ischar(varargin{1})
        gui_State.gui_Callback = str2func(varargin{1});
    end

    if nargout
        [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
    else
        gui_mainfcn(gui_State, varargin{:});
    end
    % End initialization code - DO NOT EDIT

    % --- Executes just before untitled2 is made visible.
    function untitled2_OpeningFcn(hObject, eventdata, handles, varargin)
    % This function has no output args, see OutputFcn.
    % hObject    handle to figure
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)
    % varargin   command line arguments to untitled2 (see VARARGIN)

    % Choose default command line output for untitled2
    handles.output = hObject;

    % Update handles structure

    global a;
    clear a;
    a = arduino ('com3','UNO');
    a.configureDigitalPin(3,'output')
    guidata(hObject, handles);

    % UIWAIT makes untitled2 wait for user response (see UIRESUME)
    % uiwait(handles.figure1);

    % --- Outputs from this function are returned to the command line.
    function varargout = untitled2_OutputFcn(hObject, eventdata, handles) 
    % varargout  cell array for returning output args (see VARARGOUT);
    % hObject    handle to figure
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)
    % Get default command line output from handles structure
    varargout{1} = handles.output;

    function edit1_Callback(hObject, eventdata, handles)
    % hObject    handle to edit1 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)

    % Hints: get(hObject,'String') returns contents of edit1 as text
    %        str2double(get(hObject,'String')) returns contents of edit1 as a double

    % --- Executes during object creation, after setting all properties.
    function edit1_CreateFcn(hObject, eventdata, handles)
    % hObject    handle to edit1 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    empty - handles not created until after all CreateFcns called

    % Hint: edit controls usually have a white background on Windows.
    %       See ISPC and COMPUTER.
    if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
        set(hObject,'BackgroundColor','white');
    end

    function edit2_Callback(hObject, eventdata, handles)
    % hObject    handle to edit2 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)

    % Hints: get(hObject,'String') returns contents of edit2 as text
    %        str2double(get(hObject,'String')) returns contents of edit2 as a double

    % --- Executes during object creation, after setting all properties.
    function edit2_CreateFcn(hObject, eventdata, handles)
    % hObject    handle to edit2 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    empty - handles not created until after all CreateFcns called

    % Hint: edit controls usually have a white background on Windows.
    %       See ISPC and COMPUTER.
    if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
        set(hObject,'BackgroundColor','white');
    end

    function box3_Callback(hObject, eventdata, handles)
    % hObject    handle to box3 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)

    % Hints: get(hObject,'String') returns contents of box3 as text
    %        str2double(get(hObject,'String')) returns contents of box3 as a double

    % --- Executes during object creation, after setting all properties.
    function box3_CreateFcn(hObject, eventdata, handles)
    % hObject    handle to box3 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    empty - handles not created until after all CreateFcns called

    % Hint: edit controls usually have a white background on Windows.
    %       See ISPC and COMPUTER.
    if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
        set(hObject,'BackgroundColor','white');
    end

    % --- Executes on button press in pushbutton1.
    function pushbutton1_Callback(hObject, eventdata, handles)
    % hObject    handle to pushbutton1 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)
    global a;
    a.writeDigitalPin(3,1)

    % --- Executes on button press in pushbutton2.
    function pushbutton2_Callback(hObject, eventdata, handles)
    % hObject    handle to pushbutton2 (see GCBO)
    % eventdata  reserved - to be defined in a future version of MATLAB
    % handles    structure with handles and user data (see GUIDATA)
    global a;
    a.writeDigitalPin(3,0)

and it throws me this error:

Attempt to reference field of non-structure array.

Error in untitled2>pushbutton1_Callback (line 157) a.writeDigitalPin(3,1)

Error in gui_mainfcn (line 95) feval(varargin{:});

Error in untitled2 (line 42) gui_mainfcn(gui_State, varargin{:});

Error in @(hObject,eventdata)untitled2('pushbutton1_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating uicontrol Callback

Answer 1

[Madhu Govindarajan]

The variable 'a' which stores the arduino object is being cleared. Have you checked if that is causing the issue?

[Jesus Sanchez]

Yes, that was the problem. Thanks A Lot!

[yasmine koubaa]

Please how can i check that a was cleared?

Thanks

[Oyster]

Which part should be modified?