Swift：从第二个视图控制器更新标签

Question

我有两个视图控制器。我还有一个名为number的通用变量。第一个视图控制器上有一个名为mainLabel的标签。我的第二个视图控制器上有一个按钮。按下按钮时，它应从变量number中减去200，然后更新mainLabel标签。我无法弄清楚如何使mainLabel标签在第二个视图控制器上运行。

第一视图控制器

import UIKit

var number:Int = 0

class ViewController: UIViewController {

    @IBOutlet weak var mainLabel: UILabel!

    @IBAction func backgroundButton(sender: AnyObject) {

        number = number + 1

        mainLabel.text = "\(number)"

         NSUserDefaults.standardUserDefaults().setObject(number,     forKey: "number")

    }

   override func viewDidLoad() {
        super.viewDidLoad()

        if NSUserDefaults.standardUserDefaults().objectForKey("number")     != nil {

            number =     NSUserDefaults.standardUserDefaults().objectForKey("number") as! Int

        }

        mainLabel.text = "\(number)"

    }

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

 }

第二视图控制器

import UIKit

class SecondViewController: UIViewController {

    @IBOutlet weak var buy1Label: UILabel!

    @IBAction func buy1(sender: AnyObject) {

        number = number - 200

        buy1Label.text = "Bought!"

        mainLabel.text = "\(number)"

    }

}

Answer 1

class ViewController: UIViewController {

@IBOutlet weak var mainLabel: UILabel!

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

    NSNotificationCenter.defaultCenter().addObserverForName("NSNotificationName", object: nil, queue: nil) { (note) -> Void in
        // Number changed, update your UILabel.
        var number: Int = NSUserDefaults.standardUserDefaults().integerForKey("keyOfNumber")
        self.mainLabel.text = "\(number)"
    }
}

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


@IBAction func subtractNumberBy200() {
    var number: Int = NSUserDefaults.standardUserDefaults().integerForKey("keyOfNumber")
    number -= 200
    NSUserDefaults.standardUserDefaults().setInteger(number, forKey: "keyOfNumber")
}

}

希望这对你有用。

Answer 2

哇，这个问题切入了我每天必须处理的核心问题。以下是我第一次了解如何使用通知执行此操作。

首先，设置一些常见的全局事物。

let NumberDidChangeNote = "NumberDidChangeNote" // A name for the notification.

// A function to get the value of number the same way every time.
func number() -> Int {
    return NSUserDefaults.standardUserDefaults().integerForKey("number");
}

// A function to set the value of number the same way every time.
func setNumber(number: Int) {
    NSUserDefaults.standardUserDefaults().setInteger(number, forKey: "number")
    NSUserDefaults.standardUserDefaults().synchronize()

    // Post a number did change notification
    NSNotificationCenter.defaultCenter().postNotificationName(NumberDidChangeNote, object: nil)
}

第一个视图控制器分割设置编号和设置标签的角色。

class ViewController: UIViewController {

    @IBOutlet weak var mainLabel: UILabel!

    @IBAction func backgroundButton(sender: AnyObject) {

        setNumber(number() + 1)

    }

    dynamic func numberDidChange(note: NSNotification) {

        mainLabel.text = "\(number())"

    }

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)

        // Add an observer which will call numberDidChange() anytime the number changes.
        let center = NSNotificationCenter.defaultCenter()
        center.addObserver(self, selector: "numberDidChange", name: NumberDidChangeNote, object: nil)

        // Fake an initial notification to numberDidChange() to set the initial value of the label.
        numberDidChange(NSNotification(name: NumberDidChangeNote, object: nil))
    }

    override func viewWillDisappear(animated: Bool) {

        // Remove the observer when not on the screen.
        let center = NSNotificationCenter.defaultCenter()
        center.removeObserver(self, name: NumberDidChangeNote, object: nil)

        super.viewWillDisappear(animated)
    }

}

现在第二个视图控制器根本不用担心第一个视图控制器。

class SecondViewController: UIViewController {

    @IBOutlet weak var buy1Label: UILabel!

    @IBAction func buy1(sender: AnyObject) {

        setNumber(number() - 200)

        buy1Label.text = "Bought!"

    }

}