When to create your own dll what should be in it

Question

I as of yet, have not had a need to create a dll in .NET as my programs tend to be distinct from one another (and I haven't programmed for too long). However I am starting to gather a library of regularly used methods now which tend to have copies in lots of my programs (or similar methods that could be made more generic).

As I understand it a dll should be created to share common methods between programs.

So I can put my methods in the dll, what about things like custom dialog boxes and common forms. I currently have a custom error form and a print preview dialog which are used in almost all my programs. Is it good practice to put these in a dll?

Answer 1

"Good practice" in this case really relies on how much code-duplication you're cutting down on. If these dialogues are used throughout a lot of your programs and they take up a lot of code, then yes, it's probably a good idea to move them to a shared space.

But don't be tempted to throw everything in there. You'll find yourself having to override it and by that point you're probably writing more code than you were before. Keep things simple. Keep them generic. Keep them useful.

Before you start, though, be aware that you are creating a dependency tree. If you update your library chances are you'll have to put in some time maintaining your apps that use it... But this is no different from using a third-party lib.