即使在赋值后，标签值赋值也为 nil

Question

 import UIKit
 import Foundation
class First: UIViewController {
@IBOutlet var firstTitle: UILabel!
@IBOutlet var firstTxtField: UITextField!
@IBAction func goTo2nd(sender: AnyObject) {
    var second: Second?
         second?.secondTitle.text = firstTxtField.text
}
}
import Foundation
import UIKit
class Second: UIViewController {
@IBOutlet var secondTitle: UILabel!
@IBOutlet var secondTextField: UITextField!
@IBAction func goToFirstVC(sender: AnyObject) {
    var first: First?
    first?.firstTitle.text  = secondTextField.text
}

}

为什么我无法将文本字段值分配给出线标签，我在故事板中创建了 2 个 viewController，并为每个控制器分配了这个（第一.swift，第二.swift）类

Answer 1

import UIKit
import Foundation
class First: UIViewController {

下面的这个 var 用作我们将通过在其他 swift 类中创建此类的对象来访问的属性

var firstTit:String?
@IBOutlet var firstTitle: UILabel!
@IBOutlet var firstTxtField: UITextField!
@IBAction func goTo2nd(sender: AnyObject) {
}
override func viewDidLoad() {
    super.viewDidLoad()
    firstTitle.text = firstTit
}
override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}
override func prepareForSegue(segue: (UIStoryboardSegue!), sender: AnyObject!) {
    if (segue.identifier == "goto2from1")
    {
        var svc = segue!.destinationViewController as Second;
        svc.secondTit = firstTxtField.text
    }
}
}
import Foundation
import UIKit
class Second: UIViewController {
var secondTit: String?
@IBOutlet var secondTitle: UILabel!
@IBOutlet var secondTextField: UITextField!
@IBAction func goToFirstVC(sender: AnyObject) {
}
@IBAction func goToThirdVC(sender: AnyObject) {
}
override func viewDidLoad() {
    super.viewDidLoad()
   secondTitle.text = secondTit
}
override func prepareForSegue(segue: (UIStoryboardSegue!), sender: AnyObject!) {
    if (segue.identifier == "goto1from2")
    {
        var svc = segue!.destinationViewController as First;
        svc.firstTit = secondTextField.text
    }
    else if(segue.identifier == "goto3from2")
    {
        var svc = segue!.destinationViewController as Third;
        svc.thirdTit = secondTextField.text
    }
}   
}

import Foundation
import UIKit
class Third: UIViewController {
var thirdTit:String?
@IBOutlet var thirdTitle: UILabel!
@IBOutlet var thirdTextField: UITextField!
override func viewDidLoad()
{
    super.viewDidLoad()
    thirdTitle.text = thirdTit
}
@IBAction func goTofirstFromThird(sender: AnyObject) {
}
override func prepareForSegue(segue: (UIStoryboardSegue!), sender: AnyObject!) {
    if (segue.identifier == "goto1from3")
    {
        var svc = segue!.destinationViewController as First;
        svc.firstTit = thirdTextField.text
    }
}
}

另一种方法是，如果您不想通过第二个视图控制器传递数据，但想将其直接发送到第三个视图控制器，请使用结构

import UIKit
import Foundation
class First: UIViewController {
var firstTit:String?
@IBOutlet var firstTitle: UILabel!
@IBOutlet var firstTxtField: UITextField!
@IBAction func goTo2nd(sender: AnyObject)
{
    Third.thirdGlobalVars.thirdTit = firstTxtField.text  //this line sends field data to third class' preperty (in fact a struct)
    //if u r going through 2nd vc to 3rd, to move from 1st vc to 2nd + if u want to do progammatic initialization use the following line as well
    var storyboard = UIStoryboard(name: "Main", bundle: nil)
    var vc = storyboard.instantiateViewControllerWithIdentifier("secondVC") as Second
    self.presentViewController(vc, animated: true, completion: nil)
}
override func viewDidLoad() {
    super.viewDidLoad()
    firstTitle.text = firstTit
}
override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}
}
class Third: UIViewController {
struct thirdGlobalVars {
static var thirdTit: String?
}
@IBOutlet var thirdTitle: UILabel!
@IBOutlet var thirdTextField: UITextField!
override func viewDidLoad()
{
    super.viewDidLoad()
    thirdTitle.text = thirdGlobalVars.thirdTit
}