Add custom event in C++ WinForm to inspect native collection

Add custom event in C++ WinForm to inspect native collection

I'm a learner of C++/CLI develop and recently i met a trouble about event
handler.
The question is: I wanna add a custom Event in a winForm class which
inherited System::Windows::Form, and the event must inspect a native
collect (like std::deque). Whenever the size of the queue is changed, the
event will do something.
I've tried to find the solution on MSDN already, but all i can find are
custom managed ref class which is not i need.