MATLAB: Accessing timer UserData fields

timer userdata

t=timer;
t.UserData = struct('field1', 'a', 'field2, 'b');
t.UserData.field1
% returns an error:
%inconsistently placed '.' in subscript expression
get(t.UserData, 'field1')
%returns an error:
%Conversion from double to struct not possible
get(get(t, 'UserData'), 'field1')
% returns same error
u = t.UserData;
u.field1 %works fine

Thus I have a workaround but it's kind of clunky: I set a variable to u=t.UserData at the beginning of my timer callback function and then set t.UserData=u at the end of my timercallback function

Why can't these fields be accessed directly?

Best Answer

Interesting, I had never seen that message before.

The work-around is

getfield(t.UserData, 'field1')

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MATLAB: Does the output from GUIHANDLES change after I plot to the GUI in MATLAB

This behavior is the result of a combination of the side effects of PLOT, the axes' "NextPlot" property, and the use of GUIHANDLES.

PLOT makes a call to the NEWPLOT function to determine which axes to use. Also, depending on the axes' "NextPlot" property, some of that axes' properties may be set to default values. If the property has the value "Replace", it will reset all of the axes' properties and delete all of the children of the axes. This includes the axes' "Tag" property, set to an empty string. If the "NextPlot" property is set to "ReplaceChildren", then NEWPLOT will only delete the axes' children and will not change the axes' other properties.

GUIHANDLES creates a structure containing the handles for all figure objects having a non-empty "Tag" value (thus having a valid fieldname for a structure). Since the axes' Tag will be an empty string after plotting, it will not be included in the handles structure that is output by GUIHANDLES.

There are two ways around this problem:

1) Do not use GUIHANDLES to get the "handles" structure. If you are using GUIDE and are working in a GUIDE-generated callback function, the "handles" structure will already exist as an input to the function. Also, GUIHANDLES is only intended for use in initializing the GUI. After the GUI is initialized, use the GUIDATA function to get the "handles" structure since the structure may be modified.

2) Set the axes' NextPlot property to 'replacechildren'. This way, the axes' Tag property won't be changed when PLOT calls NEWPLOT.

MATLAB: How to stop a batch file when it is running too long in MATLAB 7.13 (R2011b)

The key point is to use SYSTEM function to use Windows command ‘start’ to run the batch file and Timer object in MATLAB to check the execution. Here is a sample code.

function bla
%%Display "hello world"
disp('hello world');
%%call to command line DOS batch file
system('start run.bat');
%%create a Timer object
%  call function 'check' after 10 seconds which is defined by 
%  'StartDelay' value
t = timer('TimerFcn',@check,'StopFcn',@terminate,'UserData',false,...
            'StartDelay',10); 
start(t);
end
%%check function will set the flag t.UserData to be true, and call
%  stop function of the Timer object 
function check(t,~) 
          t.UserData = true;
          stop(t);
          delete(t);
end
%%Stop function of the Timer object which terminates DOS batch file
function terminate(t,~)
if t.UserData
      term = system('taskkill /im cmd.exe');
      % display
      fprintf('\nprocess run.bat did not finish…\n')
else
      delete(t);
end
end

Best Answer

Related Solutions

MATLAB: Does the output from GUIHANDLES change after I plot to the GUI in MATLAB

MATLAB: How to stop a batch file when it is running too long in MATLAB 7.13 (R2011b)

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