StateSet.addState

Adds the state of the specified type to the state set if it is not already present.

Note that because an #AtkStateSet is a read-only object, this method should be used to add a state to a newly-created set which will then be returned by #atk_object_ref_state_set. It should not be used to modify the existing state of an object. See also #atk_object_notify_state_change.