Notificationの登録を簡単にするextension ref: http://qiita.com/mono0926/items/e3a76dc95046f0eeeb29

file0.swift

extension UIViewController {
    // こんな感じの公開メソッドを増やしていく
    func observeKeyboard(willShowSelector: Selector, willHideSelector: Selector) -> () -> () {
        return observeNotification([
            (action: willShowSelector, name: UIKeyboardWillShowNotification),
            (action: willHideSelector, name: UIKeyboardWillHideNotification)])
    }
    func observeDidBecomeActive(action: Selector) -> () -> () {
        return observeNotification(action, name: UIApplicationDidBecomeActiveNotification)
    }

    // あるいはこちらを公開して直に使っちゃっても良いかも
    private func observeNotification(action: Selector, name: String) -> () -> () {
        return observeNotification([(action: action, name: name)])
    }
    private func observeNotification(pairs: [(action: Selector, name: String)]) -> () -> () {
        for p in pairs {
            NSNotificationCenter.defaultCenter().addObserver(self, selector: p.action, name: p.name, object: nil)
        }
        return { [unowned self] in // これ忘れるとメモリリークするので注意
            for p in pairs {
                return NSNotificationCenter.defaultCenter().removeObserver(self, name: p.name, object: nil)
            }
        }
    }
}

file1.swift

// ViewControllerのappear系で登録
removeObserverClosure = observeDidBecomeActive("didBecomeActive:")

// ViewControllerのdisappear系で登録解除
removeObserverClosure()