Per Help, in the "Pages & Classes" tab of a Declare OnChange rule you can say that the context is a PageList.

EX:

• Page Context =  .ShoppingCart()  
• Page Class = Data-Product

In the "On Change Properties" tab you would list every "interesing" Data-Product Property to watch.

Then specify an Activity with Usage = Onchange configured within the Activity's Security tab.

Hi,

Why would dynamically recalculating the sum of a list on the browser not be a good use case for the Declare OnChange? Is the argument here that for a more simple task, a Declare Expression would be more appropriate (or am I missing something more fundamental)?

Thanks,
Ben

The pattern that you are describing is using the Declare-OnChange to call an activity within which (I assume) you would perform the calculation in a property set step. This may not be as efficient as using a declare expression and raises the possibility that the property can be set by other means (by another activity or data transform for example) in which case the calculation you performed using the Declare-OnChange would no longer be valid. When you use a Declare Expression,  a single Rule is used to perform the calculation and there are built in safeguards which prevent creating another rule which attempts to set the target property value if it is already set as the result of a Declare Expression. Additionally, the rule form for the Declare Expression expression presents a more clearer view of the calculation making it easier to understand and more maintainable.