Trouble passing data between GUI callbacks

Hello!

I am working on a small utility to control and record two Watlow PID controllers via MODBUS. I am currently using MATLAB 2016b which I know does not have MODBUS support, but I am simply using this machine to do most the coding and will move over to a machine with 2017a to finalize the utility.

Here is my problem: I cannot pass data in/out of the handles structure within the recTimerCallback function. Every time the callback runs the handles structure has the same data it initially had, that is handles.Data = [] and handles.Index = 1. I'm not sure what I'm doing wrong and any help would be appreciated!

Here is my code:

function varargout = utilv3(varargin)
% UTILV3 MATLAB code for utilv3.fig
%      UTILV3, by itself, creates a new UTILV3 or raises the existing
%      singleton*.
%
%      H = UTILV3 returns the handle to a new UTILV3 or the handle to
%      the existing singleton*.
%
%      UTILV3('CALLBACK',hObject,eventData,handles,...) calls the local
%      function named CALLBACK in UTILV3.M with the given input arguments.
%
%      UTILV3('Property','Value',...) creates a new UTILV3 or raises the
%      existing singleton*.  Starting from the left, property value pairs are
%      applied to the GUI before utilv3_OpeningFcn gets called.  An
%      unrecognized property name or invalid value makes property application
%      stop.  All inputs are passed to utilv3_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 utilv3

% Last Modified by GUIDE v2.5 13-Jul-2017 14:34:03

% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
    'gui_Singleton',  gui_Singleton, ...
    'gui_OpeningFcn', @utilv3_OpeningFcn, ...
    'gui_OutputFcn',  @utilv3_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 utilv3 is made visible.
function utilv3_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 utilv3 (see VARARGIN)

%Varaibles for connecting/reading/writing the controllers
handles.T_Register = 2160;      %Thermal register to read
handles.T_IP = '192.168.1.103'; %Thermal PM IP
handles.F_Register = 2160;      %Flow register to read
handles.F_IP = '192.168.1.100'; %Flow PM IP
handles.InputReg = 360;         %Register to read from

%MODBUS Objects to communicate with the controllers
handles.ThermalBus = modbus('tcpip', handles.T_IP);    %Thermal Modbus onject
handles.FlowBus = modbus('tcpip', handles.F_IP);       %Flow Modbus object

%Variables for data aqquisition
handles.Data = [];              %Where the data will be stored
handles.Index = 1;              %Index for recording data
handles.Interval = 0.2;         %Interval in seconds between each datapoint

%Timer for continuously monitoring the process values
handles.MonTimer = timer(  'Name', 'ReadTime', ...
    'Period', 1.0, ...
    'StartDelay', 1, ...
    'TasksToExecute', inf, ...
    'ExecutionMode', 'fixedspacing', ...
    'TimerFcn', {@monTimerCallback, handles});

start(hanldes.MonTimer);

%Timer for continuously recording the process values
handles.recTimer = timer(   'Name', 'RecTime', ...
    'Period', 0.2, ...
    'TasksToExecute', inf, ...
    'ExecutionMode', 'fixedRate', ...
    'TimerFcn', {@recTimerCallback, handles});

% Choose default command line output for utilv3
handles.output = hObject;

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes utilv3 wait for user response (see UIRESUME)
% uiwait(handles.figure1);

% --- Outputs from this function are returned to the command line.
function varargout = utilv3_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 ThermalSetpointBtn.
function ThermalSetpointBtn_Callback(hObject, eventdata, handles)
% hObject    handle to ThermalSetpointBtn (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

%When the button is pressed, write the desired value to the Thermal
%Controller
Mwrite(handles.T_Register, str2double(get(handles.ThermalSetpointBox,'string')), handles.ThermalBus);

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

%When the button is pressed, write the desired value to the Flow Controller
Mwrite(handles.F_Register, str2double(get(handles.FlowSetpointBox,'string')), handles.FlowBus);

function ThermalSetpointBox_Callback(hObject, eventdata, handles)
% hObject    handle to ThermalSetpointBox (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 ThermalSetpointBox as text
%        str2double(get(hObject,'String')) returns contents of ThermalSetpointBox as a double

% --- Executes during object creation, after setting all properties.
function ThermalSetpointBox_CreateFcn(hObject, eventdata, handles)
% hObject    handle to ThermalSetpointBox (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 FlowSetpointBox_Callback(hObject, eventdata, handles)
% hObject    handle to FlowSetpointBox (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 FlowSetpointBox as text
%        str2double(get(hObject,'String')) returns contents of FlowSetpointBox as a double

% --- Executes during object creation, after setting all properties.
function FlowSetpointBox_CreateFcn(hObject, eventdata, handles)
% hObject    handle to FlowSetpointBox (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 ReadingToggleBtn.
function ReadingToggleBtn_Callback(hObject, eventdata, handles)
% hObject    handle to ReadingToggleBtn (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of ReadingToggleBtn

%Timer callback for continuously monitoring the process values and updating
%GUI text strings to match
function monTimerCallback(hObject, eventdata, handles)

%Always update the Set Point text strings
%Read the register for the thermal setpoint and update the string
set(handles.ThermalSetpointTxt, 'string', Mread(handles.F_Register, handles.ThermalBus));
%Read the register for the flow setpoint and update the string
set(handles.FlowSetpointTxt, 'string', Mread(handles.T_Register, handles.FlowBus));

%If monitoring is toggeled, update the Process Value text strings
if get(handles.ReadingToggleBtn,'value') == 1
    %Read the register for the thermal process value and update the string
    set(handles.ThermalReadingTxt, 'string', Mread(handles.InputReg, handles.ThermalBus));
    %Read the register for the flow process value and update the string
    set(handles.FlowReadingTxt, 'string', Mread(handles.InputReg, handles.FlowBus));
end

% --- Executes during object deletion, before destroying properties.
function figure1_DeleteFcn(hObject, eventdata, handles)
% hObject    handle to figure1 (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

%Stop the monitoring timer when the GUI is closed
stop(hanldes.MonTimer);

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

%Start handles.recTimer to begin recording data
start(handles.recTimer);

%Disable this button
set(handles.StartRecBtn, 'Enable', 'off');

%Enable the stop recording button
set(handles.StopRecBtn, 'Enable', 'on');

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

%Stop handles.recTimer to stop recording data
stop(handles.recTimer);

%Disable this button
set(handles.StopRecBtn, 'Enable', 'off');

%Enable the save data button
set(handles.SaveDataBtn, 'Enable', 'on');

%Timer callback for recording the process values when the user desires
function recTimerCallback(hObject, eventdata, handles)
%Write the time value to the first column
handles.Data(handles.Index, 1) = handles.Index * handles.Interval;

%Record the thermal process value
%Write the process value to the second column
handles.Data(handles.Index, 2) = Mread(handles.InputReg, ThermalBus);

%Record the flow process value
%Write the process value to the third column
handles.Data(handles.Index, 3) = Mread(handles.InputReg, FlowBus);

%Increment the index
handles.Index = handles.Index + 1;

guidata(hObject, handles);

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

%Write the recorded data to an excel file
xlswrite('TE DATA', handles.Data);

%Empty handles.Data and reset handles.Index so more data can be recorded if
%necessary
handles.Data = [];
handles.Index = 1;

%Disable this button
set(handles.SaveDataBtn, 'Enable', 'off');

%Enable the start recording button
set(handles.StartRecBtn, 'Enable', 'on');

Answer 1

[Adam]

You have to use

guidata( hObject, handles )

after assigning new data to the handles structure as the one you have in any given callback is just a local copy and goes out of scope when you do not do this.

[Zachary Adamson]

I used this command at the end of the timer callback and it still does not work.

[Adam]

handles.recTimer = timer(   'Name', 'RecTime', ...
    'Period', 0.2, ...
    'TasksToExecute', inf, ...
    'ExecutionMode', 'fixedRate', ...
    'TimerFcn', {@recTimerCallback, handles});

will not work. You need to pass the figure handle, rather than the handles structure. If you pass the handles structure as you do here then it will be embedded in at that point of the code and will never change for that callback.

Never pass handles to your own callbacks. They won't work in the same way that GUI callbacks do which take handles as an input argument

If you didn't change the figure tag then the default is figure1, if I remember correctly so:

handles.recTimer = timer(   'Name', 'RecTime', ...
    'Period', 0.2, ...
    'TasksToExecute', inf, ...
    'ExecutionMode', 'fixedRate', ...
    'TimerFcn', {@recTimerCallback, handles.figure1 });

is required, with

function recTimerCallback(src, eventdata, hGUI)
%Write the time value to the first column
handles = guidata( hGUI )

handles.Data(handles.Index, 1) = handles.Index * handles.Interval;

guidata( hGUI, handles )

and this should work.

[Zachary Adamson]

Adam,

I tried your suggestion with a few tweaks. The figure is named 'utilv3' so I tried:

handles.recTimer = timer(   'Name', 'RecTime', ...
    'Period', 0.2, ...
    'TasksToExecute', inf, ...
    'ExecutionMode', 'fixedRate', ...
    'TimerFcn', {@recTimerCallback, handles.utilv3});

but this made the program crash immediately with the error:

Reference to non-existent field 'utilv3'.

Error in utilv3>utilv3_OpeningFcn (line 86)
    'TimerFcn', {@recTimerCallback, handles.utilv3});

Error in gui_mainfcn (line 220)
    feval(gui_State.gui_OpeningFcn, gui_hFigure, [], guidata(gui_hFigure), varargin{:});

Error in utilv3 (line 42)
    gui_mainfcn(gui_State, varargin{:});

[Adam]

Did you actually change the tag of your figure in GUIDE to 'utilv3'? If not then 'figure1' is what you need to use (though I would always re-tag my main figure to the name of the GUI personally anyway).

[Zachary Adamson]

Adam,

I didn't realize it was something I had to manually change!

After changing the tag to 'utilv3' your suggestion worked flawlessly. Thank you so much for your help.

As an aside, is this considered the 'standard' way to pass data to/from a timer callback in a GUI? I am very new to using GUI's in MATLAB and the whole process has been confusing to learn.

[Adam]

I've never really used a timer callback myself, but I use a lot of listener callbacks which work the same way. Indeed any user defined callback should work the same way, although there are caveats that you have to be aware of when you end up with nested callbacks in a complicated setup (usually from listeners which cause the code to jump to another callback whilst already in one callback).

The key point is that 'handles' is nothing more than a struct. It looks a bit like some magic kind of struct because of the way it gets passed around internally in GUIDE-defined GUIs, but these do things behind the scenes that a normal user-defined callback doesn't have by default.

When you setup a function handle like the one you did, where 'handles' is an argument 'baked into' the function handle it will just be a time-stamped version of handles at the time you define the callback and will never change after that because it is just a struct locked into the function definition.

Passing the GUI handle means that you can always ask it for the latest version of handles at the point your callback is triggered, not when it was defined. You just have to make sure you aren't changing the GUI figure tag midway through the program, but there is no sensible reason to be doing that!

[Zachary Adamson]

Thank you for the explanation. You've really saved my day with your help!