You can do this in the OnItemLoad of the Repeater:
“Set value of Sum equal to [[Sum + item.Price]]”
You will also have to make sure to clear this when adding a new item. In AddItem’s OnClick:
“Set value of Sum equal to 0”
See It Live: Repeater Sum Row Example
RP File: SumRepeaterRow.rp (69.1 KB)
**A couple extra notes. I am setting the total value OnItemLoad as well, this means it sets it to all the intermediate values as well, but it doesn’t matter because the last value set is correct. You could choose to use the total [[Sum]] value at another place though.
Also, watch out for other Actions that will make the Repeater refresh (e.g. setting a filter, deleting rows). This will call OnItemLoad for all the Repeater Items again and if you do not clear your [[Sum]] to 0 first in those Actions you will end up doubling and tripling, etc… it.