At the time that
prepare(for segue... is called, your outlets have not been assigned yet. Your view must be loaded before your outlets are assigned. You can force the view to load simply by accessing it (
detailView.view), but this is a bad idea. A better approach would be to assign another property on your view controller with the value you're trying to pass around, then in
viewDidLoad of your detail view controller, set the properties you wish to set on your IBOutlets.