swift中代理的使用   

• 首先定义一份协议。

  protocol DetailsViewControllerDelegate: NSObjectProtocol{
      func fetchBackString(str: String)
  }

• 声明代理属性

  weak var delegate: DetailsViewControllerDelegate?

• 遵守代理并实现

  class ViewController: DetailsViewControllerDelegate

  let VC = segue.destination as! DetailsViewController
  VC.delegate = self

  //MARK: - DetailsViewControllerDelegate(代理)
  func fetchBackString(str: String) {
      NSLog(str, "")
  }

• 使用

  delegate!.fetchBackString(str: "代理返回数据:\(area.name)")