public abstract unowned VariantType? get_action_state_type (string action_name)
Queries the type of the state of the named action within this.
If the action is stateful then this function returns the VariantType of the state. All calls to change_action_state must give a Variant of this type and get_action_state will return a Variant of the same type.
The state type of a particular action will never change but it is possible for an action to be removed and for a new action to be added with the same name but a different state type.
the name of the action to query
the state type, if the action is stateful