:) Thanks for all the suggestions you give!!!

SeeBees wrote: expose an extra property, say Generation{get{}}, Not really, if your Collection inherits from an existing one, you can implement your own public override IEnumerator GetEnumerator() just like the original collection did. :) Luc Pattyn [Forum Guidelines] [My Articles] This month's tips: - before you ask a question here, search CodeProject, then Google; - the quality and detail of your question reflects on the effectiveness of the help you are likely to get; - use PRE tags to preserve formatting when showing multi-line code snippets.

SeeBees wrote: For example, I have a folder containing 50 pictures of size 3000 * 2000. No wonder... In order to generate the thumbnail, GDI is loads the entire file into memory then generates the thumbnail. GDI+ is a generalized library, preferring compatibility over speed. If you want to improve performance, you'll need to find a third party graphics library that gives you the perfromance features you need. Figure out what your requirements are, then go shopping. A guide to posting questions on CodeProject[^] Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic      2006, 2007

Not exactly answering your question, but the general advice is to avoid using PictureBoxes, and do your own custom painting directly. -- Help me! I'm turning into a grapefruit! Buzzwords!

Thanks for your helpful explanation.:-D

My earlier answer wasn't quite as correct as I would have preferred. :-D You need the abstract stub, but it's still not an implementation.

Thanks for your advice!:-O