I've got this method that I keep copying and pasting into different solutions so I figured I'd post it here in case someone else could benefit from it. You would think that it would be really easy to create folders in a list or library but oddly enough (or, if you've done SharePoint development long enough you would say typically enough), it's not. So, here's a simple little method to help you get a folder and have it created if it doesn't already exist:
The code is actually not that bad. It takes in a web and a list (although I could have/should have modified it to just take in the list and get the web via the ParentWeb property, but I digress) and a folder. After checking to see if it already exists it then splits the folder path on "/" and then loops through each creating the folders as it goes (if it doesn't already exist). So you'd call the method like this:
SPFolder folder = list.GetFolder("/subfolder1/subfolder1a");
Update 7/11/2008: Per the suggestion in the comments I changed the code so that the method is an extension method instead.