如何从模态视图控制器将数据传递回视图控件

Question

so usually I would use a delegate pattern for this but this is a tricky situation.

View controller A presents -> view controller B which presents -> view controller C.

When the user finished the steps in view controller C, I will dismiss both B and C in one call with

   self.presentingViewController?.presentingViewController?.dismiss(animated: true, completion: nil)

I would like to pass the data from view controller C back to A. How is this possible, since A has no reference to C, how can I implement a delegate?

****EDIT: This is all done programmatically, so I cant use unwind segues

***** SOLUTION *******

The best solution I found was to just add an observer in VC A and post the object in VC C when dismissing the VC:

self.presentingViewController?.presentingViewController?.dismiss(animated: true) {
        NotificationCenter.default.post(name: Notification.Name("UpdateKeywords"), object: self.account)
    }

Dont forget to remove the observer in VC A in deinit()

Answer 1

我通常要做的是在b中创建对A的引用，然后在C中创建对该引用的引用，然后在返回A之前，对引用进行更改，然后调用self.presentingViewController?.presentingViewController?.dismiss(animated: true, completion: nil)

Answer 2

you can use singleton design pattern. Declare a singleton class for datas.

class DatasSingleton{
    static let sharedInstance = DatasSingletonSingleton()
    var datas: int = 0
}

in class C you set data

class C{
    func xyz(){
        DatasSingleton.sharedInstance.datas = 6
    }
}

in class A you can read data

class A{
    func xyz(){
        print(DatasSingleton.sharedInstance.datas)
    }
}

Answer 3

The example code, VC A present VC B, VC B present VC C, at VC C you enter text, and then the method of VC A is called (here the data is transferred) with the text entered at VC C. See below...

Hope that helps

(Xcode 8.1 (8B62): Delete storyboard, launchscreen, Clean properties Main story board and Launchscreen in Info.plist and replace AppDelegate.swift with the following content)

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        self.window = UIWindow(frame: UIScreen.main.bounds)
        self.window!.rootViewController = Avc()
        self.window!.makeKeyAndVisible()
        return true
    }
}

class Avc: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let b = self.view.addSubviewWithConstraints(["b" : Button(title: "Open B VC")], constraints: ["V:|-10-[b(70)]", "H:|-10-[b]-10-|"])["b"]
        (b as! Button).action = {() in
            let bvc = Bvc()
            bvc.action = self.receiveData
            self.present(bvc, animated: false,completion: nil)
        }
    }

    func receiveData(data: String?) {
        print(data)
    }
}

class Bvc: UIViewController {
    var action: ((_ data: String?)->())!
    override func viewDidLoad() {
        super.viewDidLoad()
        let b = self.view.addSubviewWithConstraints(["b" : Button(title: "Open C VC")], constraints: ["V:|-10-[b(70)]", "H:|-10-[b]-10-|"])["b"]
        (b as! Button).action = {() in
            let cvc = Cvc()
            cvc.action = self.action
            self.present(cvc, animated: false,completion: nil)
        }
    }
}

class Cvc: UIViewController {
    var action: ((_ data:String?)->())!
    override func viewDidLoad() {
        super.viewDidLoad()
        let t = self.view.addSubviewWithConstraints(["t" : UITextField()], constraints: ["V:|-50-[t(24)]", "H:|-10-[t]-10-|"])["t"]
        (t as! UITextField).backgroundColor = UIColor.white
        let b = self.view.addSubviewWithConstraints(["b" : Button(title: "Transfer data to A VC")], constraints: ["V:|-100-[b(90)]", "H:|-10-[b]-10-|"])["b"]
        (b as! Button).action = {() in
            self.presentingViewController?.dismiss(animated: true, completion: nil)
            self.presentingViewController?.presentingViewController?.dismiss(animated: true, completion: nil)
            self.action((t as! UITextField).text)
        }
    }
}



class Button: UIButton {
    var action: (()->())!
    init(title: String) {
        super.init(frame : CGRect.zero)
        self.setTitle(title, for: UIControlState())
        self.addTarget(self, action: #selector(Button.buttonAction(_:)), for: .touchUpInside)
    }
    required init?(coder: NSCoder) {super.init(coder: coder)}
    func buttonAction(_ sender: AnyObject) {if action != nil {action()}}
}

extension UIView {
    func addSubviewWithConstraints(_ views: [String : AnyObject], constraints: Array<String>) -> [String : AnyObject] {
        for (_, view) in views {
            self.addSubview(view as! UIView)
            (view as! UIView).translatesAutoresizingMaskIntoConstraints = false
        }
        for i in 0 ..< constraints.count {self.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: constraints[i], options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views))}
        return views
    }
}