設定button正常狀態的標題

button有各種狀態，不過我們最常用的非normal狀態莫屬。但是，在新版的SDK裡 (搭配Xcode 8)，定義button狀態的UIControlState型別竟找不到normal !

public struct UIControlState : OptionSet {
public init(rawValue: UInt)
public static var highlighted: UIControlState { get } // used when UIControl isHighlighted is set
public static var disabled: UIControlState { get }
public static var selected: UIControlState { get } // flag usable by app (see below)
@available(iOS 9.0, *)
public static var focused: UIControlState { get } // Applicable only when the screen supports focus
public static var application: UIControlState { get } // additional flags available for application use
public static var reserved: UIControlState { get } // flags reserved for internal framework use
}

天啊! 我們再也無法設定button的標題了 ! 當然不可能，Apple只是把事情變得更簡單，現在呼叫function setTitle(_:for:)時，只要在for參數傳入[ ]即可設定button正常狀態的標題。

let button = UIButton()
button.setTitle("愛瘋一切為蘋果的彼得潘", for: [])