How to pass in a list of Strings to an Apex Action in new Flow Builder?

Question

I have a simple screen flow, which takes in a case Cancel Reason, and if that reason is Other, will get allow a user to specify the other reason via text entry.

We have an Apex server method called CancelCaseInvocable, which calls common case cancelation logic shared by other code.

I can see the Apex @InvocableMethod and it provides a place to specify the input and output values. The actual server method takes a List<String> and returns the same.

I have created a local flow variable called Args, which is a text collection variable. I have added the necessary args to the variable but when I try to select the variable in the Cancel Case Apex Action, I do not see the Args variable.

Here you can see that I create a test non-collection Text variable, which is visible, but the Args collection Text variable is not:

How do I pass a List<String> into the Apex Action when I cannot select a collection variable as an input argument?

Answer 1

The InvocableMethod interface is bulkified. This allows you to map flows within Process Builder in a bulkified manner. As the documentation states, your parameter must be...

A list of a primitive data type or a list of lists of a primitive data type – the generic Object type is not supported.

This means that to pass in a collection, you actually need to use List<List<String>> (or whichever other type you need), and to pass in a normal variable, you need to use List<String>.