GUI setting default value to text box

I am trying to set a default to the Text box or the slider, but this is not working as the text box does not show the default value:

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

% Last Modified by GUIDE v2.5 27-Jun-2019 13:56:22

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

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

% Update handles structure
guidata(hObject, handles);

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


% --- Outputs from this function are returned to the command line.
function varargout = GPEC_Task_Generator_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;


% --- Executes on slider movement.
function Num_Task_Callback(hObject, eventdata, handles)
% hObject    handle to Num_Task (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
Num_Task_Val = round(hObject.Value);
set(handles.Num_Task, 'Value', Num_Task_Val);
set(handles.Num_Task_Disp, 'String', Num_Task_Val);

% Hints: get(hObject,'Value') returns position of slider
%        get(hObject,'Min') and get(hObject,'Max') to determine range of slider


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

% Hint: slider controls usually have a light gray background.
if isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
    set(hObject,'BackgroundColor',[.9 .9 .9]);
end


% --- Executes during object creation, after setting all properties.
function Num_Task_Disp_CreateFcn(hObject, eventdata, handles)
% hObject    handle to Num_Task_Disp (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    empty - handles not created until after all CreateFcns called
Num_Task_Disp_Val = str2double(get(hObject,'string'))
if isnan(Num_Task_Disp_Val)
     set(handles.Num_Task_Disp, 'String', '5');
end


% --- Executes on button press in Next_Button.
function Next_Button_Callback(hObject, eventdata, handles)
% hObject    handle to Next_Button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
disp('Next')


% --- Executes on button press in Cancel_Button.
function Cancel_Button_Callback(hObject, eventdata, handles)
% hObject    handle to Cancel_Button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
disp('Cancel')
close(GPEC_Task_Generator)

Error:

Struct contents reference from a non-struct array object.

Error in GPEC_Task_Generator>Num_Task_Disp_CreateFcn (line 108)
     set(handles.Num_Task_Disp, 'String', '5');

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

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

Error in
matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)GPEC_Task_Generator('Num_Task_Disp_CreateFcn',hObject,eventdata,guidata(hObject))

[Peng Zhao]

error line:

set(handles.Num_Task_Disp, 'String', '1')

[Rik]

What is the exact error message? It looks like your variable should exist and the assignment should work as intended.

[Peng Zhao]

I have updated the code.

[Rik]

If you set a breakpoint at that line, what are the sizes of the variables involved? handles should be scalar struct, and the Num_Task_Disp field should be a scalar uicontrol object handle.

After fixing this, you could also consider replacing that line with the line below

set(hObject, 'String', '5')

[Peng Zhao]

I was able to set the default within the opening function:

% --- Executes just before GPEC_Task_Generator is made visible.
function GPEC_Task_Generator_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 GPEC_Task_Generator (see VARARGIN)
Num_Task_Val_Default = 1;
set(handles.Num_Task, 'Value', Num_Task_Val_Default);
set(handles.Num_Task_Disp, 'String', Num_Task_Val_Default);
% Choose default command line output for GPEC_Task_Generator
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

But thanks for helping.