How can I get the opposite value of a Bool in Swift?

Question

My specific case is I am trying to toggle the nav bar hidden and showing.

    let navHidden = !self.navigationController?.navigationBarHidden
    self.naviga         


        

Answer 1

The exclamation point is on the wrong side of the boolean. The way you've written it would indicate that the boolean could be nil. You want !navHidden.

Answer 2

navHidden is an optional. And you explictely unwrap that optional (which means you get a crash if navHidden is nil). Clearly something is wrong here. I suggest

if let navController = self.navigationController {
    let navHidden = navController.navigationBarHidden
    navController.setNavigationBarHidden (!navHidden, animated:true)
}

Answer 3

navHidden! is to make sure this is not optional. !navHidden is the correct way to do that.

From Apple's book.

Trying to use ! to access a non-existent optional value triggers a runtime error. Always make sure that an optional contains a non-nil value before using ! to force-unwrap its value.