how to encapsulate an entire system and then fit future change?(details inside)

[dotNeter]

I have a GUI system and I'm gotta build a new system upon it. My
requirement is,

1. The new system will have a set of new interfaces, that means the
GUI system should be invisible to users.
2. The new system shouldn't simply wrap all interfaces, since some new
non-UI features would get added.
3. The underlying GUI system may entirely get substituted someday.

I'm trying to use the bridge pattern to design the system. I'm
planning to add a middle, totally abstract, system, which defines all
required interfaces, and definitely it should reflect all original
inheritance relationship between widgets. Sth like,
NewSystem -> AbstractSystem -> RealImplementedSystem

However, the problem is that, you know, the GUI system has lots of
different interfaces on different widgets, so that the abstract system
is hard to build. It should be only composed of pure abstract classes
in one inherited tree, which reflects the relationship between
widgets. Another problem is that even if I get this middle abstract
system, it would be a tough work to implement it. I gotta repeatedly
code so much similar interfaces which may just redirect the operation
to underlying real system.

Any other way for the design? Thx in advance.

 

[Victor Bazarov]

I have a GUI system and I'm gotta build a new system upon it. My
requirement is,
[..]

However, the problem is [..]

Any other way for the design? Thx in advance.

Have you looked at the systems that already exist and get used by
countless programmers all over the world, like Qt, X, wxWidgets,
or similar?

V