As mentioned by Mike earlier, there are 3 datasource options for a ListView:
2. Database + XPath
Long story short: The database and microflow options support sorting, and the association option does not.
So I guess the real question is: Can we add sorting capabilities to the Association option in a future version of Mendix modeller?
The typical way to handle this limitation is to use a microflow datasource:
From the Mendix documentation:
The list view supports the following types of data sources: database source, XPath source, association source and microflow Source. The database and XPath sources retrieve objects from the database and supports searching and sorting. The database source can also be used in offline applications. The association source follows an association from the enclosing data view to get to the objects. Finally, the microflow source calculates the list of objects by executing a microflow.
So you can't sort with an association source. I think you'll need to change your source or create an interim entity with the objects sorted as you want them to be sorted...
Unless someone else in the community has a workaround.
Solved using dedicated MF and Button