flex - Design pattern for 2 linked items -

suppose have following visual custom components:

2 blocks: & b

1 link: c, connecting block & b

now, if either block or b change, link c has updated.

i never sure how handle this.

do :

a) pass both block & b line c can add event listener each of them , act when change happens.

b) pass link c both block & b when block changes can notify link.

c) make parent of both blocks , link responsible updating components.

i feel common problem, wonder if there sort of design pattern describing best approach.

any appreciated.

after reading seems mediator pattern might want.