i turn on and off led with mathlab by using the gui but when i push button "On" it errro

Hello. My name is kongporyou . 

could you help me . I have problame with gui when i push button "On" it not work and error line 42 (underline)

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

Error in matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)poryou('pushbutton1_Callback',hObject,eventdata,guidata(hObject))
 
Error while evaluating UIControl Callback.

function varargout = poryou(varargin)
% PORYOU MATLAB code for poryou.fig
%      PORYOU, by itself, creates a new PORYOU or raises the existing
%      singleton*.
%
%      H = PORYOU returns the handle to a new PORYOU or the handle to
%      the existing singleton*.
%
%      PORYOU('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in PORYOU.M with the given input arguments.
%
%      PORYOU('Property','Value',...) creates a new PORYOU or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before poryou_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to poryou_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 poryou

% Last Modified by GUIDE v2.5 26-Mar-2020 13:49:29

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @poryou_OpeningFcn, ...
                   'gui_OutputFcn',  @poryou_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 poryou is made visible.
function poryou_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 poryou (see VARARGIN)

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

% Update handles structure
guidata(hObject, handles);
delete(instrfind({'Port'},{'COM4'}));
clear all;
clc;
global a;
 a = arduino('COM4','Uno');

could you help me plese!

Thanks, best reguard.

[Geoff Hayes]

Kong - you will need to show the code for pushbutton1_Callback since tht is where the error is occurring. I recommend against using global variables and suggest storing the data (that you want available between callbacks) in the handles structure. The code for the poryou_OpeningFcn would become

% --- Executes just before poryou is made visible.
function poryou_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 poryou (see VARARGIN)
% Choose default command line output for poryou
handles.output = hObject;

delete(instrfind({'Port'},{'COM4'}));
handles.a = arduino('COM4','Uno');    % <---- save the arduino object to handles

% Update handles structure
guidata(hObject, handles);            % <---- update handles object

[Kong Poryou]

Yes thanks you so much.