If the argument you specify to an action builder takes an argument, the Evaluate Argument
input is displayed in the builder call editor. This input allows you to specify when the argument is to be evaluated.
The two main cases where this input is useful are:
When the Action is Run
Use this choice get the value the user just entered in a form passed to your method. A typical example of this might be when the user enters a code in a form, and a button calls a method passing the value that the user typed.As the page is rendered
Repeated region loop variables provide a use case for this choice. In this case, you want the current value as the page is being rendered. A typical example of this case is a repeated region with a link inside. Here you want to use a part of the repeating data to be able to tell which link was clicked, so you pass it as an argument to a method.
The builders that provide this input (Button, Link, HTML Action, and so on) will attempt to detect these two cases and warn you if your selection is inappropriate. In most cases, you can accept to take the default choice provided.
Parent topic: Using input mappings for builder calls in a repeated region: wpf7