Extended problem

I would like to add a new problem in addition to the original problem specified below. One of the user controls in the application contains a list of objects that I need to access from another user control. How can this be done? (I don't believe the division into controls is very well performed, but I'd rather not change it..)

Should I do it by events as with the original problem, or should I get hold of the parent Form, and use it to find the instance of the control, and expose it as a property?

Original problem

I have two user controls in a form that I want to be able to communicate with each other. Usercontrol A should be able to start an operation on B.

What is the preferred way of solving this? Should the form wait for an Event from A, and then start the operation on B? Any design pattern for this? Or is it an even easier solution?

Thanks in advance! :)

The two user controls should not have any knowledge of each other. If you want to always deal with them as a pair, consider creating a third user control to house them.

Should the form wait for an Event from A, and then start the operation on B?

Yes, this is the only good way to handle this.

The extended (bonus?) problem is a bit trickier. I would handle this by having the form pass the user control a delegate to a method on the other user control to retrieve the data. The user control can then invoke the delegate method to call the method on the other control without having any knowledge of its implementation.