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My specific case is I am trying to toggle the nav bar hidden and showing.
let navHidden = !self.navigationController?.navigationBarHidden
self.navigationController?.setNavigationBarHidden(navHidden!, animated: true)
Is not working for me like it normally would in Obj-C.
374
The "and" ( && ) operator returns true if the boolean value to its left and the boolean value to its right are true. And the "not" ( ! ) operator returns the opposite of the boolean value to its right. That is, true becomes false and false becomes true .
Swift NOT Operator ! is used to perform logical NOT operation on a boolean operand. ! symbol is used for Logical NOT Operator in Swift. NOT Operator takes one boolean value as operands on its right and returns the logical NOT of the operand.
To toggle a boolean, use the strict inequality (! ==) operator to compare the boolean to true , e.g. bool !== true . The comparison will return false if the boolean value is equal to true and vice versa, effectively toggling the boolean.
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.
129
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.
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