C# - WebUserControls Get Type Infomation About Other WebUserControls Within The Project?

I'm basically trying to get webcontrols to talk to one another.I have one WUC that wants to get information from another.In ControlB's GetDataFromControlA method

public List<ControlBData> GetDataFromControlA()
{
ControlA c = Page.FindControl( IdOfControlA) as ControlA;
if( c != null)
{
return c.Data;
}
...
}

At code time ControlB knows nothing of ControlA...so ControlB cant access its members, and the above wont compile.

I'm thinking I have to use methods in the page to get the controls talking to one another...