OnSelect for a field to trigger an action on a variable?

[#1]

In my UI have a calendar object tied to a variable called vDate. When you select a date in the calendar, the variable triggers and filters results based on the date selected and the value of a field called "Type".

The field "Type" has a listbox in the UI and I want the vDate trigger to activate when a value in field "Type" changes. What is the correct way of activating a variable trigger from a trigger tied to a different field?