NSLayoutConstraint Programming

在iOS裡用storyboard建立UI和拉layoutConstraint是很方便、易學及快速的，但純程式碼建立UI也是很多人會選擇的方式，畢竟Xcode的storyboard速度實在有點慢。

用程式碼設定LayoutConstraint，要建立這樣的畫面

這樣簡單的畫面就要這麼多行

所以可以幫UIView建立一個Extention，來設定LayoutConstraint

extension UIView {
  func setConstraint(topA: NSLayoutYAxisAnchor, topConstraint: CGFloat?, leadingA: NSLayoutXAxisAnchor, leadingConstraint: CGFloat?, bottomA:NSLayoutYAxisAnchor, bottomConstraint: CGFloat?, trailingA: NSLayoutXAxisAnchor, trailingConstraint: CGFloat?) {
    self.translatesAutoresizingMaskIntoConstraints = false
    if topConstraint != nil {
      self.topAnchor.constraint(equalTo: topA, constant:     topConstraint!).isActive = true
    }
    if leadingConstraint != nil {
      self.leadingAnchor.constraint(equalTo: leadingA, constant: leadingConstraint!).isActive = true
    }
    if bottomConstraint != nil {
      self.bottomAnchor.constraint(equalTo: bottomA, constant: -bottomConstraint!).isActive = true
    }
    if trailingConstraint != nil {
      self.trailingAnchor.constraint(equalTo: trailingA, constant: - trailingConstraint!).isActive = true
    }
  }
}

這樣要在建立一個View設定LayoutConstraint就輕鬆多囉!