Circular References, Memory Leaks, and other Baddies

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In a garbage collected environment such as .NET, it is possible to unwittingly leave objects in a state where the garbage man will be "on vacation". One way to check on this kind of stuff is with profiling products such as the Scitech .NET Memory Profiler: http://www.scitech.se/memprofiler/

Ian Griffiths has a well - written, concise piece on this subject here: http://www.interact-sw.co.uk/iangblog/2004/07/07/circulareventrefs

One of the issues we found with this is when you have a lot of controls on a UserControl or form and you unwind it, thinking you have gotten rid of everything.

Except, you may have not done so - event handler delegate calls may still hold a reference to their target. We found this to be especially noticeable on controls derived from RichTextBox - a control with a lot of Interop going on under the hood and notoriously "Buggy" to boot.

The problem is solved with a neat little method we call in the Dispose Block , "UnregisterChildControls":

private void UnRegisterChildControl(Control ctrl)
{
if (ctrl is CustomCheckBox)
{ CustomCheckBox cb = (CustomCheckBox)ctrl;
cb.CheckedChanged -= new EventHandler(cb_CheckedChanged);
}

else if (ctrl is CustomDateComboBox)
{
CustomDateComboBox cmb = (CustomDateComboBox)ctrl;
cmb.DateSelected -= new DateSelectedHandler(cmb_DateSelected);
}
}

-- By "cleaning up our room" in this manner, we've seen those scary looking memory consumption profiles flatten out very nicely. :-)
Peter has been active on the C# and other MS newsgroups, has had samples at gotdotnet.com (now codegallery.com) that have been downloaded over 56,000 times, and has written numerous articles for eggheadcafe.com, for which he is a co-founder, and MSDNAA sites. He has also been a technical reviewer on books from Prentice Hall, Manning and other publishers. Peter was a Microsoft MVP for 10 years. Peter was born and raised in New York City, and after a stint as a jazz musician playing contrabass with the Robert Hunt Trio, migrated to sunny Florida, where he was hired as a rookie Financial Consultant at Merrill Lynch in Orlando, specializing in Corporate Services. It was at Merrill that Peter realized computers and technology were his forte. He spent his last few years at Merrill developing real – time computerized trading and and stock charting program using advanced technical analysis indicators, some of which are his own inventions. In 1997, he moved on to architect and serve as lead developer on a number of innovative web-based and middleware solutions for the healthcare and financial services industry.

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