ios - NotificationCenter 在 Swift 中传递数据

Question

我正在使用 Swift 3 开发一个测试项目。我正在尝试使用 NotificationCenter 将 textField 字符串从一个类传递到另一个类。我正在尝试从此链接中找出答案:pass NSString variable to other class with NSNotification和 how to pass multiple values with a notification in swift

我从上面的链接中尝试了几个答案，但没有任何效果。

我的代码:

//第一个VC

import UIKit


extension Notification.Name {        
public static let myNotificationKey = Notification.Name(rawValue: "myNotificationKey")    
}


class ViewController: UIViewController {

@IBOutlet weak var textView: UITextView!

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.
}


@IBAction func sendData(_ sender: AnyObject) {

    let userInfo = [ "text" : textView.text ]
    NotificationCenter.default.post(name: .myNotificationKey, object: nil, userInfo: userInfo)

}

}

//第二VC

 import Foundation
 import  UIKit

 class viewTwo: UIViewController {

@IBOutlet weak var result: UILabel!



override func viewDidLoad() {


}


override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    NotificationCenter.default.addObserver(self, selector: #selector(self.notificationReceived(_:)), name: .myNotificationKey, object: nil)
}

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    NotificationCenter.default.removeObserver(self, name: .myNotificationKey, object: nil)
}

func notificationReceived(_ notification: Notification) {
    guard let text = notification.userInfo?["text"] as? String else { return }
    print ("text: \(text)")

    result.text = text
}

我不确定代码有什么问题。上面，我从第一个链接找到的最初标记为已回答的代码。代码已转换为 Swift。

Answer 1

不要使用对象参数来传递数据。它旨在过滤具有相同名称但来自特定对象的通知。因此，如果您在发布通知时传递了一些对象，而在添加观察者时传递了另一个对象，您将不会收到它。如果你传递 nil，你基本上关闭了这个过滤器。

您应该改用 userInfo 参数。

首先，最好将通知的名称定义为Notification.Name 的扩展名。这种方法更安全，更易读:

extension Notification.Name {        
    public static let myNotificationKey = Notification.Name(rawValue: "myNotificationKey")    
}

发布通知:

let userInfo = [ "text" : text ]
NotificationCenter.default.post(name: .myNotificationKey, object: nil, userInfo: userInfo)

订阅:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    NotificationCenter.default.addObserver(self, selector: #selector(self.notificationReceived(_:)), name: .myNotificationKey, object: nil)
}

取消订阅:

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    NotificationCenter.default.removeObserver(self, name: .myNotificationKey, object: nil)
}

要调用的方法:

func notificationReceived(_ notification: Notification) {
    guard let text = notification.userInfo?["text"] as? String else { return }
    print ("text: \(text)")
}