ios - 通过委托(delegate)将数据传递给各种 View Controller

Question

努力学习通过 delegates 传递数据的基础知识.我正在尝试从我的 viewController 传递一个字符串给我的viewController2并打印出来。我收到错误消息:

"Type ViewController2 has no member delagate" in my view controller 2.

我无法弄清楚我哪里出错了。

View Controller 1:

protocol datadelagate {
    func printThisString(string: String)
}

class ViewController: UIViewController {

    var delegate: datadelagate?

    override func viewDidLoad() {
        delegate?.printThisString(string: "This was passed from first controller to second controller")
    }
}

这是我的 View Controller 2:

class ViewController2: UIViewController, datadelagate {

    func printThisString(string: String) {
        print(string)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        ViewController2.delagate = self
        print(String.self)
    }
}

Answer 1

如果你想要ViewController2从 ViewController 打印一些值，您可能必须这样做:

protocol datadelagate {
    func printThisString(string: String)
    func getStringFromVC1() -> String
}

class ViewController: UIViewController, datadelagate {

    let someString: String = "From VC1"

    func printThisString(string: String) {
        print(string)
    }

    func getStringFromVC1() -> String {
        return someString
    }

    override func viewDidLoad() {
        ViewController2.delagate = self

    }
}

class ViewController2: UIViewController {

    var delegate: datadelagate?

    override func viewDidLoad() {
        super.viewDidLoad()

        //This is how something from VC2 is sent to VC1's scope.
        delegate?.printThisString(string: "Calling the delegate to print something from ViewController2 on first ViewController")

        //The below call gets you some value from VC1. (This is what you wanted, I belive...)
        print(delegate?.getStringFromVC1())
    }
}

现在进行一些解释:

为便于理解，假设 delegate作为从事某些特定工作的人( protocol )。

你有一个“委托(delegate)”

你要求你的委托(delegate)和你的 friend 一起工作，你的 friend 承认了。 (通过 You.delegate = self 分配您的委托(delegate)，其中 self 是您的 friend )

现在，通过您的delegate ，您可以通过询问您的delegate 与您的 friend 一起做某事做一些工作(在 protocol 中定义)。

编辑

上面的代码不起作用，因为非静态数据成员试图在不创建实例的情况下被访问

工作代码

import UIKit

class ViewController2: UIViewController {

    static let sharedInstance = ViewController2()
    weak var delegate: DataDelagate?

    override func viewDidLoad() {
        super.viewDidLoad()
        //This is how something from VC2 is sent to VC1's scope.
        delegate?.printThis(string: "Calling the delegate to print something from ViewController2 on first ViewController")

        //The below call gets you some value from VC1. (This is what you wanted, I belive...)
        print(delegate?.getStringFromVC1() ?? "s")
    }
}

class ViewController: UIViewController {

    static let sharedInstance = ViewController2()
    var someString: String = "From VC1"

    override func viewDidLoad() {
        super.viewDidLoad()
        ViewController2.sharedInstance.delegate = self
    }
}
extension ViewController: DataDelagate {
    func printThis(string: String) {
        print(string)
    }

    func getStringFromVC1() -> String {
        return someString
    }
}

protocol DataDelagate: AnyObject {
    func printThis(string: String)
    func getStringFromVC1() -> String
}