Pickers are rather odd controls in that they appear much like a textbox but can behave like a choice control. As such, one can’t simply use a “transfer data” rule action to populate them.
Let’s say you have a picker control on an item view. Below it is a list view. The list view populates after initializing, so page 1 of a full list of widgets appears when the form loads. The user is generally expected to start typing the name of a widget into the picker and tabbing off of it to let the picker resolve and shape the list.
But let’s say you wanted to allow a double-click from a list item to populate that picker and filter that list. Creating a rule driven by the list item double-click is a good way to go, but using a “transfer data” action will get you nowhere.
You’ll have to use a “Populate a list control with data” action instead. The picker will be recognized as a list control. You’d configure the rule by providing whatever input properties are associated with the List() method of its SmartObject, with options to filter and to sort. Save it, check it in, and run it to see it working!