Comments on: Understanding Object Cleanup

By: Kieran Parsons

Kieran Parsons — Thu, 30 Jul 2009 12:17:31 +0000

The very helpful Mathworks technical support team were able to help me out with #6. Their solution is posted at http://www.mathworks.com/support/solutions/en/data/1-ABQ59D/index.html if anyone is interested. An interesting use of strings in callbacks instead of anonymous functions.

By: Kieran Parsons

Kieran Parsons — Fri, 17 Jul 2009 18:10:57 +0000

I am trying to clean up a singleton GUI object (using a persistent variable as suggested in 2 and http://www.mathworks.com/access/helpdesk/help/techdoc/index.html?/access/helpdesk/help/techdoc/matlab_oop/bru6n2g.html.)

When the object is created I create a GUI figure window, and I want them to always exist as a pair. I have added a ‘CloseRequestFcn’ callback that closes the figure and deletes the object if a user hits the close button. This works fine. However, I cannot figure out how to get the GUI figure to close if I clear the singleton object. I tried overloading the ‘delete’ method(which normally works) but in the case of the clearing of a persistent object it seems that the ‘delete’ method is not called.

Any ideas?

Thanks,
Kieran

By: StephenLL

StephenLL — Wed, 30 Jul 2008 19:32:32 +0000

Nick, Loren, Gautam:

Thank you for replying and your ideas. I have a lot to learn and experiment with now.

I don’t plan to make wide spread use of this technique for the obvious pitfalls like hidden dependence, but there is some functionality well served by it.

Thanks again.

Stephen

By: Gautam Vallabha

Gautam Vallabha — Wed, 30 Jul 2008 16:41:59 +0000

Another example of user-managed objects are graphics objects (FIGURE, AXES, PATCH, LINE, etc.). Nick’s guidelines work for these as well:
1) There is a DELETE function for the graphics objects
2) There is a FINDALL function that can be used to catch all the HG objects, including those with visibility set to ‘off’.

With regard to Stephen’s question: one guideline for building user-managed objects is to allow the user to assign a unique name to the object. This makes it easy to find them later. For example:

———–
timer(’period’,0.25, ‘name’, ‘myTimer’);

% much later … in some other function
h = timerfind(’name’, ‘myTimer’);
stop(h);
delete(h);
———–

This strategy works with pretty much all user-managed objects in MATLAB.

By: Loren

Loren — Tue, 29 Jul 2008 17:27:03 +0000

Stephen-

If you do use persistent variables, you have to be careful about how multiple instances of the class work. Today you have 2 more choices that don’t limit you to a singleton pattern, nested functions or the object system introduced in R2008a. There will be a blog on the latter coming soon. In the meantime, check out the documentation on the class system.

–Loren

By: Nick Haddad

Nick Haddad — Tue, 29 Jul 2008 17:18:59 +0000

There aren’t any guidelines per say, but persistent variables would be a great way of keeping some data around if one of your object’s variables goes out of scope.

You could also create a MATLAB class that implements the Singleton design pattern using static methods and a persistent variable. This would give you a nice interface to some data that stays around in memory, but doesn’t require an object variable at all.

For more info on singleton see Wikipedia:
http://en.wikipedia.org/wiki/Singleton_pattern

By: StephenLL

StephenLL — Tue, 29 Jul 2008 14:01:11 +0000

Great article.

Is there any documentation or guidelines for building “User-Managed Objects”?

The only way I can think of building a function like this is using persistent variables.

Other then GUIs, I can see other situations where these will be convenient such as utilities. a logging utility comes to mind, also an enumerator class.

Thanks again.
Stephen