// Example of using KeyboardNotification to update an NSLayoutConstraint

import UIKit

final class ViewController: UIViewController {

    // Outlet for a layout constraint that specifies distance from bottom of
    // a subview to the bottom of the view.
    // 
    // This constraint will be updated when the keyboard appears, disappears,
    // or changes size.
    @IBOutlet weak var bottomLayoutConstraint: NSLayoutConstraint!
    
    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)

        NSNotificationCenter.defaultCenter().addObserver(self,
            selector: "keyboardWillChangeFrameNotification:",
            name: UIKeyboardWillChangeFrameNotification,
            object: nil)
    }

    override func viewDidDisappear(animated: Bool) {
        NSNotificationCenter.defaultCenter().removeObserver(self)
        super.viewDidDisappear(animated)
    }

    func keyboardWillChangeFrameNotification(notification: NSNotification) {
        let n = KeyboardNotification(notification)
        let keyboardFrame = n.frameEndForView(self.view)
        let animationDuration = n.animationDuration
        let animationCurve = n.animationCurve

        let viewFrame = self.view.frame
        let newBottomOffset = viewFrame.maxY - keyboardFrame.minY

        self.view.layoutIfNeeded()
        UIView.animateWithDuration(animationDuration,
            delay: 0,
            options: UIViewAnimationOptions(rawValue: UInt(animationCurve << 16)),
            animations: {
                self.bottomLayoutConstraint.constant = newBottomOffset
                self.view.layoutIfNeeded()
            },
            completion: nil
        )
    }
}