In one of the applications I'm working on, I have a ListBox that presents a set of files to the user. The purpose of the program is to do some kind of processing on these files. I need the user's input during parts of the processing, otherwise I would just totally automate the thing that not bother the user at all. In any case, to begin processing a file, the user must double-click on one of the entries in the ListBox. When it's done, the entry is removed automatically.
The only other control in my form is a Done button, to indicate to the user that they're "done." Clicking it just closes out the form, so perhaps it's not really necessary at all, but not putting in a button sort of breaks our "pattern." In most of our other applications that have a ListBox, we also have at least two buttons; a Print button to print off the results (because the results are other pieces of data that were compiled as part of a report) and a Cancel button that closes out the form for the user. However, I don't feel that a Print/Cancel or even an OK/Cancel button combination is appropriate here (the user isn't going to need a report of the files to process). Really all the user can do is either process a file or leave the form.
But now I'm being told that the Done button is confusing to our users, and that I need to redesign it somehow. I was asked as to why I didn't use some kind of OK/Cancel combo, but as I just explained it didn't make any sense in the context of this form.
I'm really not sure what to type into Google to research this very specific problem, so I thought I'd get the StackOverflow community's opinion. If I have a form with a list that can be double-clicked to do some work on an individual item, what else (if anything) does the form need? What should I use in place of Done button? Is double-clicking in the list even the best option? If the user didn't know that they're suppose to double-click in the list to begin a process, how would I convey to them that they must do so? What would be the most user-intuitive approach to take in this given context?