GUI handles reference to non-existent field 'timer'

After initiating the code below the GUI appears, but if I try to press any of the buttons I get a Reference to non-existent field 'timer' error. I have changed the GUI visibility to on, and am still getting this error. See code and full error text below.

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ERROR

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Reference to non-existent field 'timer'.

Error in Boid_GUI>Start_Callback (line 91)

start(handles.timer)

Error in gui_mainfcn (line 95)

feval(varargin{:});

Error in Boid_GUI (line 42)

gui_mainfcn(gui_State, varargin{:});

Error in

matlab.graphics.internal.figfile.FigFile/read>@(hObject,eventdata)Boid_GUI('Start_Callback',hObject,eventdata,guidata(hObject))

Error while evaluating UIControl Callback.

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CODE

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

% Last Modified by GUIDE v2.5 27-Feb-2020 23:38:53

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

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

% Update handles structure
guidata(hObject, handles);

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


handles.N = 20; % define the number of boids
% initialize boids position and velocity
boid.pos = 5000.*rand(handles.N,2);
boid.vel = [150.*rand(handles.N,1) 10.*rand(handles.N,1)];
boid_plotter(boid,handles)	% call the function to plot the boids in the GUI window
% create timer object 
handles.timer = timer;
set(handles.timer,'TimerFcn',{@my_callback_fun,handles},'Period',.1)

set(handles.timer,'ExecutionMode','fixedRate','UserData',boid)

% --- Outputs from this function are returned to the command line.
function varargout = Boid_GUI_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 button press in Start.
function Start_Callback(hObject, eventdata, handles)
% hObject    handle to Start (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
start(handles.timer)

% --- Executes on button press in Stop.
function Stop_Callback(hObject, eventdata, handles)
% hObject    handle to Stop (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
stop(handles.timer)

% --- Executes on button press in Reset.
function Reset_Callback(hObject, eventdata, handles)
% hObject    handle to Reset (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
stop(handles.timer)
% initialize boids position and velocity
boid.pos = 5000.*rand(handles.N,2);
boid.vel = [150.*rand(handles.N,1) zeros(handles.N,1)];
set(handles.timer,'UserData',boid)


% --- Executes on slider movement.
function slider3_Callback(hObject, eventdata, handles)
% hObject    handle to slider3 (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,'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 slider3_CreateFcn(hObject, eventdata, handles)
% hObject    handle to slider3 (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 on slider movement.
function slider4_Callback(hObject, eventdata, handles)
% hObject    handle to slider4 (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,'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 slider4_CreateFcn(hObject, eventdata, handles)
% hObject    handle to slider4 (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 on slider movement.
function slider5_Callback(hObject, eventdata, handles)
% hObject    handle to slider5 (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,'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 slider5_CreateFcn(hObject, eventdata, handles)
% hObject    handle to slider5 (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


function my_callback_fun(obj,event,handles)
 
% get data
boid = get(obj,'UserData');
% move boids
[boid.pos,boid.vel] = move_all_boids(boid.pos,boid.vel,handles);
% plot boids
boid_plotter(boid,handles)
% update data
set(obj,'UserData',boid);

%-----------------------------------------------------------------------

function boid_plotter(boid,handles)
h  = axis(handles.axes1);
plot(boid.pos(:,1),boid.pos(:,2),'o')
axis([0 5000 0 5000]);
set(gca,'XTick',[],'YTick',[])
hold on
for i=1:size(boid.vel,1)
    plot([boid.pos(i,1) boid.pos(i,1)+boid.vel(i,1)],...
	       [boid.pos(i,2) boid.pos(i,2)+boid.vel(i,2)],'r')
end
hold off

function [pos,vel] = move_all_boids(pos,vel,handles)
h = findobj(gcf,'Style','slider');
behavior_strength = get(h,'Value');
% cycle through all boids
for i=1:size(pos,1)
 
    % calculate behaviorial velocity maneuvers
    separation = 1*behavior_strength{1}*avoid(pos,i,200);
    allignment = 5*behavior_strength{2}*match_vel(vel,i);
    cohesion = .5*behavior_strength{3}*center_of_mass(pos,i);
    % update boid 
    vel(i,:) = vel(i,:) + separation + allignment + cohesion;
    % keep velocity magnitude constant (150)
    vel(i,:) = 150*(vel(i,:)/norm(vel(i,:)));
    % update position and restrict the values within the plot axis (mod.m,      %   modulus function)
    pos(i,:) = mod(pos(i,:) + vel(i,:),5000);
end

%---------------------------------------------------------------
function v1 = center_of_mass(pos,i)
% function to move each boid towards the precieved 
% center of mass of the rest of the flock
 
% percieved center of mass 
pc = (sum(pos,1) - pos(i,:))/(size(pos,1)-1);
% move the boid towards the center by 1%
v1 = 0.01*(pc - pos(i,:));   
%---------------------------------------------------------------
function v2 = avoid(pos,i,dist)
% function to move each boid away from other boids
v2 = [0 0];
for k = 1:size(pos,1)
    if k ~= i
        if norm(pos(i,:) - pos(k,:)) < dist
            v2 = (pos(i,:) - pos(k,:))-v2 ;
        end
    end
end
%---------------------------------------------------------------
function v3 = match_vel(vel,i)
% function to match each boids velocity with near birds
% note: same as rule one but with velocity rather than position
pv = (sum(vel,1) - vel(i,:))/(size(vel,1) - 1);
v3 = 0.01*(pv - vel(i,:));

Answer 1

[Geoff Hayes]

While your code in the Boid_GUI_OpeningFcn function is adding the timer to the handles structure, you are only modifying the "local" copy of it. If you want to save these changes to this structure, then you need to call guidata so that all other callbacks (from that point on) receive the updated version of handles. So in the Boid_GUI_OpeningFcn just do

% --- Executes just before Boid_GUI is made visible.
function Boid_GUI_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 Boid_GUI (see VARARGIN)
% Choose default command line output for Boid_GUI
handles.output = hObject;
% UIWAIT makes Boid_GUI wait for user response (see UIRESUME)
% uiwait(handles.figure1);
handles.N = 20; % define the number of boids
% initialize boids position and velocity
boid.pos = 5000.*rand(handles.N,2);
boid.vel = [150.*rand(handles.N,1) 10.*rand(handles.N,1)];
boid_plotter(boid,handles)	% call the function to plot the boids in the GUI window
% create timer object 
handles.timer = timer;
set(handles.timer,'TimerFcn',{@my_callback_fun,handles},'Period',.1)
set(handles.timer,'ExecutionMode','fixedRate','UserData',boid)
% Update handles structure
guidata(hObject, handles);

I just moved the line guidata(hObject, handles); to the end of the function. Note that whenever you make a change to handles you always need to call guidata in this manner.

[Geoff Hayes]

Also, be careful with this line of code

set(handles.timer,'TimerFcn',{@my_callback_fun,handles},'Period',.1)

You are passing a copy of handles structure as it is now as an input parameter to the callback. If this structure changes over time (by other callback, etc.) then this input to the timer callback will not. Typically, if I want my timer callback to have access to the handles structure, I pass in the handle to the GUI figure and then request the handles structure from within the callback. For example,

set(handles.timer,'TimerFcn',{@my_callback_fun,handles.figure1},'Period',.1)

and then in the callback

function my_callback_fun(obj,event,hFigure)
% get the handles structure
handles = guidata(hFigure);

% get data
boid = get(obj,'UserData');
% etc.

[4007william]

Thank you for the help and tips!