What's the OOP way of dealing with a flow control heavy application?

Question

I'm refactoring a huge WPF application whose complexity stems from the way it deals with flow control. It has a lot of "tiny business rules" that make it really difficult to make a modification without breaking something. These rules are things like

If the window mode is foo but this is the first time they've pressed this button and the user has a certain role, show this, else validate another thing and show that, else show another thing.

I've thought about creating a lot of different classes for validation and keeping the global state but I'm not sure if there's a design pattern or something focused on dealing with this kind of situation.

• gnat: Possible duplicate of Style for control flow with validation checks
• Robert Harvey: If you're not already doing so, a Model-View-ViewModel (MVVM) approach eases this problem considerably. See markwithall.com/programming/2013/03/01/…

Answer 1

One approach that might fit is a finite state machine. There are tools that help you build and visualize them but you can also model it with standard OOP practices.