使用闭包和代理和Segue进行反向传值

import UIKit

class FirstViewController: UIViewController, SecondViewControllerDelegate {

    @IBOutlet weak var showTextLabel: UILabel!
    @IBOutlet weak var showDelegateTextLabel: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }
    
    //点击按钮跳转到SecondViewController
    @IBAction func tapGoSecondViewController(sender: UIButton) {
        //从storyboard上加载SecondViewController
        let secondVC = UIStoryboard(name: "Main", bundle: NSBundle.mainBundle()).instantiateViewControllerWithIdentifier("secondViewController") as! SecondViewController
        //实现回调，获取回调回来的值 （闭包）
        secondVC.backClosure = {
            (backStr: String) -> Void in
            self.showTextLabel.text = backStr
        }
        secondVC.delegate = self
        //跳转到SecondViewController
        self.navigationController?.pushViewController(secondVC, animated: true)
    }
    //MARK: - SecondViewControllerDelegate(代理)
    func fetchBackString(str: String) {
        self.showDelegateTextLabel.text = str
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}