CODEWITHSUNDEEP
swiftxcodeswift3
Horia
Horia

Reputation: 26

Swift specific notification observer initialization

While trying to use the new Swift NotificationCenter, I am trying to create observer objects as properties (against the classic Obj-C pattern of assigning observers to self):

private let keyboardWillShowObserver = {
    return NotificationCenter.default.addObserver(forName: .UIKeyboardWillShow, object: nil, queue: nil, using: self.keyboardWillShow(_:))
}()

private func keyboardWillShow(_ notification: Notification) {
    bottomVerticalSpaceConstraint.constant = 400
}

The problem is that I get the following error message, even though I have the member function part of the same class:

Value of type '(NSObject) -> () -> MyAwesomeViewController' has no member 'keyboardWillShow'

Upvotes: 0

Views: 801

Answers (2)

abjurato
abjurato

Reputation: 1469

Since your keyboardWillShowObserver is not lazy, it's closure will be executed during instance initialization of MyAwesomeViewController. As far as I understand, that means self will be interpreted as MyAwesomeViewController class but not the instance of class.

There is an easy way to fix this error: make private lazy var keyboardWillShowObserver so the closure will be executed on instance after it will be completely initialized.

Upvotes: 1

Abdelahad Darwish
Abdelahad Darwish

Reputation: 6067

HomeViewController is your viewController 

  private let keyboardWillShowObserver = {
        return NotificationCenter.default.addObserver(forName: .UIKeyboardWillShow, object: nil, queue: nil, using: { (Notification) in
            HomeViewController.keyboardWillShow (Notification)
        })

    }()

     static func keyboardWillShow(_ notification: Notification) {
       // bottomVerticalSpaceConstraint.constant = 400
    }

Upvotes: 1

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