Remember that a Variable is a place holder for another part, much like a parameter in 3GL programming languages. Use a Variable part to pass an object to a view.
You set the type of object the variable will contain by changing the variable's type. You do this by selecting Change Type from the variable's pop-up menu and typing a class name.
When you make connections to the variable, you are really making connections to another part. The variable receives the identity of that part at run time.