InfoPath Dev

I am populating an infopath MultiSelect box at runtime, by setting its datasource to a group of fields. It is working great.

However, when attempting to select multi items, I am at a loss. I can't find a IsSelected property and I can't loop through all the controls in a strongly typed fashion and get the items. How does one achieve this?

I have the items I want to check in a CommaDelimitedStringCollection but can put in a collection of any type. I am indifferent to performance considerations.

Just to clarify, I am programtically populating an infopath form and On loading I need to programtically select items in a mslb. So if given the values 1,2,3 and those values are in a mslb with values 1,2,3,4,5,6 how to select 1,2,3