How can I add item data to QComboBox from Qt Designer/.ui file

Edit: Because this answer seems to be getting more upvotes than it should. I'll leave it here, because a lot of people seem to find this answer when they google for their problem. The answer below is much better suited to OP's question.

In QT designer 5.6.2 you can double-click the combo-box to add items.

Ok, so I actually went through the source code of the uic and found the spot that handles QComboBox. As of the current version of Qt (so 5.5.1), there is no support for setting the data attribute of the items through the .ui files. I may make this a feature request, but for now, it's unsupported.