Icon.FromHandle: should I Dispose it, or call DestroyIcon?

Question

I use Win32 SHGetFileInfo to get a handle to the icon belonging to a certain file. There are a lot of descriptions how to do this, also on stackoverflow, for instance: Get i

Answer 1

The .NET Icon class is remarkably clumsy, taking care of this yourself is required. The MSDN article for SHFILEICON makes no bones about it, you must call DestroyIcon(). And so does the MSDN article for Icon.FromHandle(). The exact moment in time you call DestroyIcon matters a great deal as well, it must be delayed until some code either has made a copy of the icon or until you no longer need the icon and would normally call its Dispose() method.

Beware of the code snippet in the MSDN article, it shows a scenario where DestroyIcon() is called early. Okay in that specific case since it is assigned to the Form.Icon property. A corner case and surely not what you want to do.

The only really decent way to deal with this is to override the behavior of Icon.FromHandle() and force the object to take ownership of the native icon handle. So that it will automatically call DestroyIcon() when you dispose it. That requires a hack, the Icon constructor that lets you do this is internal. Reflection to the rescue, you can use the code from this post, note the GetConstructor() call. Start feeling good about it by writing a little unit test that does this a million times. If you hate it then write your own IDisposable wrapper so you can both dispose the icon and pinvoke DestroyIcon().