ios - Swift 委托(delegate) - 新手 3 ViewController

Question

所以这是我的问题。我从 Swift 和 C# 开始了我的旅程，我正在尝试以最简单的方式学习委托(delegate)。

我创建了一个 xcode 项目，在其中设置了 3 个 View Controller 。我创建了 2 个 Segue:

1. 我可以从firstViewController (firstVC) 转到secondViewController (secondVC)
2. 我可以从firstViewController转到thirdViewController(thirdVC)

应用程序用途:

1. 从第一个VC转到第二个VC，点击一个按钮，关闭 View 并根据点击的按钮更新标签。 -- 这个很简单。

2. 从第一个 VC 转到第三个 VC，点击那里唯一的按钮，关闭 View 并使用一些简单的文本更新与之前相同的标签 - 这也完成了。

3. 如果我点击 ThirdVC 中的按钮，我想更改 SecondVC 中的标签

第三个对我来说并不容易。

代码如下:

第一个 View Controller :

import UIKit

class FirstViewController: UIViewController, SecondViewControllerDelegate, ThirdViewControllerDelegate {

@IBOutlet weak var answerLabel: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "firstToSecondSegue" {
        let secondVC = segue.destinationViewController as! SecondViewController
        secondVC.delegate = self
    } else if segue.identifier == "firstToThirdSegue" {
        let thirdVC = segue.destinationViewController as! ThirdViewController
        thirdVC.delegate = self
    }
}

@IBAction func answerButtonTapped(sender: UIButton) {
    if sender.tag == 0 {
        performSegueWithIdentifier("firstToSecondSegue", sender: self)
    } else if sender.tag == 1 {
        performSegueWithIdentifier("firstToThirdSegue", sender: self)
    }
}

func giveTheAnswer(yes: Bool) {
    if yes {
        print("Yes is the answer")
        self.answerLabel.text = "I do like chicken!"
    } else {
        print("No is the answer")
        self.answerLabel.text = "I do not like chicken!"
    }
}

func iWantPie(kindOfPie: String, disableButton: Bool) {
    if kindOfPie == "Apple pie" {
        print("Textlabel will change to applepie.")
        self.answerLabel.text = "Fu*k chicken. Let's eat apple pie!"
    }
    if disableButton {
        print("DisableButton set to true")
        self.answerLabel.backgroundColor = UIColor.redColor()
    }
}
}

第二个 View Controller :

protocol SecondViewControllerDelegate {
func giveTheAnswer(yes: Bool)}


class SecondViewController: UIViewController, ThirdViewControllerDelegate {

@IBOutlet weak var theOnlyLabel: UILabel!
@IBOutlet weak var yesButton: UIButton!
@IBOutlet weak var noButton: UIButton!

var delegate: SecondViewControllerDelegate?

override func viewDidLoad() {
    super.viewDidLoad()


    // Do any additional setup after loading the view.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@IBAction func answerButtonPressed(sender: UIButton) {

    if sender.tag == 0 {
        //Yes tapped
        self.delegate?.giveTheAnswer(true)
        dismissViewControllerAnimated(true, completion: nil)
    } else if sender.tag == 1 {
        //No Tapped
        self.delegate?.giveTheAnswer(false)
        dismissViewControllerAnimated(true, completion: nil)
    }
}

func iWantPie(kindOfPie: String, disableButton: Bool) {
    print("Function iWantPie in secondViewController is Running")
    if disableButton == true {
        print("DisableButton running")
        self.theOnlyLabel.text = "Pie was tapped"
    }

}}

第三 View Controller :

protocol ThirdViewControllerDelegate {
func iWantPie(kindOfPie: String, disableButton: Bool)}

class ThirdViewController: UIViewController {

var delegate: ThirdViewControllerDelegate?


override func viewDidLoad() {
    super.viewDidLoad()    

    // Do any additional setup after loading the view.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@IBAction func piePressed(sender: UIButton) {
    self.delegate?.iWantPie("Apple pie", disableButton: true)
    dismissViewControllerAnimated(true, completion: nil)

}}

Answer 1

请通过在 if else 条件中添加断点来检查以下代码是否正常工作。

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "firstToSecondSegue" {
        let secondVC = segue.destinationViewController as! SecondViewController
        secondVC.delegate = self
    } else if segue.identifier == "firstToThirdSegue" {
        let thirdVC = segue.destinationViewController as! ThirdViewController
        thirdVC.delegate = self
    }
}

还要检查您是否为 Storyboard 中的 segue 提供了正确的 segue 标识符。“firstToSecondSegue”和“firstToThirdSegue”