How do I implement a timer function that updates a static text box within my GUI?

My goal is to have a countdown show in a static text box while the user is answering math facts. The timer function as implemented in the code below displays an error of "Not enough input arguments"

Is there a syntax issue with my use of the timer or something more fundamental about how timers work within the GUI that I'm missing to properly execute this task?

function varargout = flashcard_app(varargin)
% FLASHCARD_APP MATLAB code for flashcard_app.fig
%      FLASHCARD_APP, by itself, creates a new FLASHCARD_APP or raises the existing
%      singleton*.
%
%      H = FLASHCARD_APP returns the handle to a new FLASHCARD_APP or the handle to
%      the existing singleton*.
%
%      FLASHCARD_APP('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in FLASHCARD_APP.M with the given input arguments.
%
%      FLASHCARD_APP('Property','Value',...) creates a new FLASHCARD_APP or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before flashcard_app_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to flashcard_app_OpeningFcn via varargin.
%
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @flashcard_app_OpeningFcn, ...
                   'gui_OutputFcn',  @flashcard_app_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 flashcard_app is made visible.
function flashcard_app_OpeningFcn(hObject, eventdata, handles, varargin)

handles.output = hObject;

% Initiate timer and callback function:
handles.timer = timer('Period',1,'TimerFcn',@timerCallback); 

% Update handles structure
guidata(hObject, handles);

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

% --- Outputs from this function are returned to the command line.
function varargout = flashcard_app_OutputFcn(hObject, eventdata, handles) 
varargout{1} = handles.output;

% --- Executes on button press in start_button.
function start_button_Callback(hObject, eventdata, handles)

%Begin Timer Function:
set(handles.timer_value,'String','10');
start(handles.timer);

function timerCallback(hObject, eventdata, handles)
disp('Timer Function Executing')
current_timer = get(handles.timer_value,'String');
sprintf('The current timer value is %d', current_timer)
t = str2double(current_timer);
t = t-1;
new_timer = num2str(t);
sprintf('The new timer value is %d', new_timer)
set(handles.timer_value,'String',new_timer)
guidata(hObject,handles);

Answer 1

[Sean de Wolski]

You need to pass handles into the callback

@(t,e)timerCallback(t,e,handles)

Also, why aren't you using app designer?

doc appdesigner