NotificationCenter在Swift中传递数据

Question

我正在研究Swift 3中的测试项目。我正在尝试使用NotificationCenter将textField字符串从一个类传递到另一个类。我正试图通过以下链接来解答答案：pass NSString variable to other class with NSNotification和how to pass multiple values with a notification in swift

我从上面的链接尝试了几个答案，但没有任何效果。

我的代码：

//第一次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)

}

}

// SecondVC

 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，代码最初标记为答案，我从第一个链接中找到。代码已转换为Swift。

Answer 1

不要使用object参数传递数据。它旨在过滤具有相同名称但来自特定对象的通知。因此，如果在addObserver发布通知和另一个对象时传递了一些对象，则不会收到它。如果你传递nil，你基本上会关闭这个过滤器。

您应该使用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)
}

退订：

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)")
}

Answer 2

使用userInfo传递文本，这是一个可选的字典类型[AnyHashable：Any]？在Swift 3.0中它是[NSObject：AnyObject]？在swift 2.0中

@IBAction func sendData(_ sender: UIButton) {

// post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: ["text": textValue.text])

print(textValue) // textValue printing

}

viewDidLoad

中的

//注册接收通知

NotificationCenter.default.addObserver(self, selector: #selector(self. incomingNotification(_:)), name:  NSNotification.Name(rawValue: "notificationName"), object: nil)

和incomingNotification

func incomingNotification(_ notification: Notification) {
if let text = notification.userInfo?["text"] as? String {
   print(text)
  // do something with your text   
}


}

Answer 3

在sendData方法传递textField.text到Notification对象和incomingNotification中执行此操作：

guard let theString = notification.object as? String else {
    print("something went wrong")
    return 
}

resultLabel.text = theString

您还可以使用块在控制器之间传递数据。

Answer 4

使用dispatchQueue，因为您的通知是在加载视图之前发布的。因此，请延迟通知邮件。

@IBAction func sendData(_ sender: AnyObject) {

    let userInfo = [ "text" : textView.text ]
      DispatchQueue.main.asyncAfter(deadline: .now() + 0.15) {
 NotificationCenter.default.post(name: .myNotificationKey, object: nil, userInfo: userInfo)        }

}