Help urgent ! Error while evaluating uicontrol Callback

Hi ! Any idea why this is happening and how to fix it?

Thanks,

[Stephen23]

Globals make code buggy and hard to debug.

You have a bug with a global variable... and now the extremely difficult task of trying to debug it. Good luck. A much better approach would be to write code without globals, then the code is less buggy and also easier to debug: "I have never seen MATLAB code where globals were the right thing to do.... Most of the time I have seen globals being used it was a situation where the code author did not understand scoping of variables. Rather than pass variables from one function to another, they were just being made global."

http://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/

Passing arguments is much more robust, and is the recommended way of passing data between workspaces:

http://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

https://www.mathworks.com/matlabcentral/answers/14857-where-do-people-learn-bad-programming-habits-i-e-goto-global-and-eval

https://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

https://www.mathworks.com/matlabcentral/answers/74626-how-to-declear-global-array-and-how-to-use-it

etc etc

[andrei cosmin]

This is the code. Can you help me solve the error? :( I will be grateful, thank you!

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/29922-why-your-question-is-not-urgent-or-an-emergency

Answer 1

[Walter Roberson]

Your code relies upon Legacy Arduino, suitable for MATLAB R2011a to R2013b only. It calls upon install_arduino which is defined by that particular support package, and it uses pinMode(), which was replaced, as I discuss in https://www.mathworks.com/matlabcentral/answers/304583-no-appropriate-method-property-or-field-pinmode-for-class-arduino#answer_236196

Your code is not suitable for demonstrating any reasonably current version of MATLAB: it will fail for R2014a or later.

In the version range that it works for, your code would crash at the location it does if you have not first clicked on the STABILESTE CONEXIUENEA button to initialize the arduino connection. Your code will also have problems if you do not click on START as well.

Your code will fail when you click on START if you are not using a PC, as the code expects to be able to access the winvideo video adapter.

[andrei cosmin]

@Walter Roberson , thank you for the answer. Can you tell me how is it possible to install this package? I use Matlab2012a!

[Walter Roberson]

There is a Download link on that page.

[Walter Roberson]

The link I gave above, https://www.mathworks.com/matlabcentral/fileexchange/32374-legacy-matlab-and-simulink-support-for-arduino, has a Download link. Click on that to download ArduinoIO.zip into a convenient location that is not under the MATLAB installation directory. Unzip the .zip

Run MATLAB as administrator (just one time for the purpose of installing the package) by right-clicking on the MATLAB icon and selecting "Run as Administrator". This will allow the updated path to be saved.

Then from MATLAB, cd to the directory created when you unzipped the file, and launch the "install_arduino" command, this will simply add the relevant ArduinoIO folders to the matlab path and save the path. You can then exit the "Run as Administrator" MATLAB session and start a new MATLAB session.

Your .m contains a call to install_arduino which should probably be commented out.

[andrei cosmin]

Thank you very much for the answer! I solved the problem!

[Robert Adam]

poti sa imi spui si mie care era problema si de ce aparea aceasta eroare?..multumesc anticipat!

Answer 2

[Guillaume]

As per Stephen's comment, you have a bug with your global variables. Either, your callback is being executed before whichever function is supposed to set a to the correct value had a chance to do so, or some function has changed the global a to an invalid value. Either way, when the callback is executed a is not yet/no longer a structure and you get your error.

As Stephen said, globals are a bad idea, precisely for this reason. It's very difficult to track what happens to them; any function can modify their value. It's also difficult to make sure that they're initialised in the right order, particularly when you use asynchronous functions such as callback.

You now have two options:

• go over the whole of your program and check the flow to see when a is supposed to be set to the correct value (can be anywhere in the code), see where it is being changed (again can be anywhere) and make sure that this always happen before there's a chance your callback is called.
• radically modify your code to use recommended practices such as gui handles

Neither is going to be quick. The second approach would ultimately serve you better.

Oh, and by the way: why-your-question-is-not-urgent-or-an-emergency

[andrei cosmin]

I need for the license and I urgently need it in 2 weeks I have to teach it. Could you help me, please solve the problem? Thx for replay !!!

[Jan]

@andrei: Please do not try to push the voluntary helpers. This seems impolite and is counter-productive. It is your turn to solve the problem. See https://www.mathworks.com/matlabcentral/answers/29922-why-your-question-is-not-urgent-or-an-emergency .

Creating a larger code based on the communication by global variables is a really bad idea. Professional programmers would avoid this strictly, because they know, that fixing a bug in such code is terribly ugly. Now you expect them to debug your code.

I cannot even read the screenshots. Prefer to post text by copy&paste.

Stephen's comment and Guillaume's answer are valuable help already. Follow the given advices. It is unlikely that others will fix your code, when you do not even try to do this by your own.

[andrei cosmin]

@simon I've attached the source code, I'm not a matlab master. It's the first time I work with him.

[Jan]

@andrei cosmin: What do you expect me to do with your code? Do you think that I will edit and fix it for you? You think that your problem is urgent, becasue you have to "teach it" in two weeks? Then this is ther perfect moment to learn how to use clean programming techniques and avoid globals strictly.

If I fix your code, wou will miss the chance to learn how to do this. This would not help you to teach it or use it for teaching or what ever your job is.

It would be unprofessional to fix your code. Working inside ugly code written by others is a brown-field project. If there is no really good reason (masured in ten thousands of dollars or months of work), the best method to cleaning up a brown-field project is to delete the code and re-write it from scratch. Fiddeling in failing code is extremely prone to errors. Guessing the intention of other ones code is expected to fail. Especially globals are such ugly, that I would not even fix my own code, if it suffers from them.

The best advice I can give you is:

Remove the globals and replace them by fields of the handles struct. Search in the forum for "share data between callbacks" - the problem is discussed daily. And after you have implemented this, you will be a nice step closer to beeing a Matlab master! :-)

Alternatively you can ask someone to fix your code professionally. This will most likely include, that the original code is deleted and re-written from scratch. And of course such a service must include a salary. A good professional programmer might write + document + test this in an hour and costs 160 $ per hour. A beginner might need 8 hours at a price of 20 $ per hour. As usual the actual work will take twice as long as estimated (measured in time and money), even if you take this rule into consideration.

[Walter Roberson]

Why do your uicontrol style text have KeyPressFcn set to '%automatic' ??

Answer 3

[ismail tas]

ı have similer problem in Matlab Gui . I want to desing calculator. Every toggle button dont have any problem but answer button have problem and it gives Error while evaluating UIControl Callback.

[Walter Roberson]

You should start a new Question for this, and you should include your code and the .fig, and a complete copy of the error message.