Here are some things that can fix this (in increasing order of difficulty):
- Clean the project (Product > Clean)
-
Manually paste in
@IBOutlet weak var viewName: UIView! // or @IBAction func viewTapped(_ sender: Any) { }
and control drag to it. (Change type as needed.) Also see this.
-
Completely close Xcode and restart your project.
- Delete the Derived Data folder (Go to Xcode > Preferences > Locations and click the gray arrow by the Derived Data folder. Then delete your project folder.)
- Click delete on the class, remove reference (not Move to Trash), and add it back again. (see this answer)