在Swift中从视图控制器传回对象

Question

我有三个使用推式选择器的视图控制器-OneVC，TwoVC和ThreeVC。 在OneVC上，将创建一个名为firstObject的对象，并在用户填写文本字段时设置其值。 除了创建的对象称为secondObject以外，TwoVC上也会发生类似的情况。 这些对象通过prepareForSegue（）传递给下一个视图控制器。

从ThreeVC-> TwoVC中移动“返回”时，textFields保持填充。

TwoVC-> OneVC，仍然填写文本字段。

我要修复的是从OneVC-> TwoVC再次前进时，TwoVC中的文本字段已清除，但我希望它保留以前填写的内容，并在第一次时设置为secondBrand.someValue。 我猜想这与我如何在TwoVC中初始化secondObject有关。 我应该在这里做什么？

这是我的代码：

对象自定义类：

class Object {
    var someValue: String = ""
}

OneVC：

class OneVC: UIViewController {

    var firstObject: Object!

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

        self.firstObject = Object()
    }

    @IBAction func textFieldDidChange(textField: UITextField) {
        firstObject.someValue = textField.text!
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "OneToTwoSegue" {
            let twoVC = segue.destinationViewController as! TwoVC
            twoVC.firstObject = firstObject
        }
    }
}

TwoVC：

class TwoVC: UIViewController {

    var firstObject: Object!
    var secondObject: Object!

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

        self.secondObject = Object()
    }

    @IBAction func textFieldDidChange(textField: UITextField) {
        secondObject.someValue = textField.text!
    }


    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "TwoToThreeSegue" {
            let threeVC = segue.destinationViewController as! ThreeVC
            threeVC.firstObject = firstObject
            threeVC.secondObject = secondObject
        }
    }
}

ThreeVC：

class ThreeVC: UIViewController {
    @IBOutlet weak var firstObjectLabel: UILabel!
    @IBOutlet weak var secondObjectLabel: UILabel!

    var firstObject: Object!
    var secondObject: Object!

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

        firstObjectLabel.text = "firstObject.someValue = \(firstObject.someValue)"
        secondObjectLabel.text = "secondObject.someValue = \(secondObject.someValue)"
    }
}

源代码

Answer 1

听起来好像您想在释放对象之前将对象从第二个ViewController传回到第一个ViewController，然后再次将其传递到第二个ViewController并在文本字段中显示。

为了将对象传回，请创建委托协议。 例如，创建一个名为“ Protocol.swift”的文件：

protocol writeValueBackDelegate {
    func writeValueBack(value: String)
}

在第一个ViewController上，在加载第二个VC时设置委托。 现在，您可以在第二个ViewController中保存对象。

最终代码如下所示：

class Object {
    var someValue: String = ""
}

OneVC：

class OneVC: UIViewController, writeValueBackDelegate {

var firstObject: Object!
var secondObject: Object!

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

    self.firstObject = Object()
    self.secondObject = Object()
}

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

@IBAction func textFieldDidChange(textField: UITextField) {
    firstObject.someValue = textField.text!
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "OneToTwoSegue" {
        let twoVC = segue.destinationViewController as! TwoVC
        //set OneVC to be a delegate for a TwoVC
        twoVC.delegate = self

        twoVC.firstObject = firstObject
        twoVC.secondObject = secondObject
    }
}

func writeValueBack(value: String) {
    // This is my value from my second View Controller
    print("first:" + value)
    self.secondObject.someValue = value
}
}

TwoVC：

class TwoVC: UIViewController {

var delegate: writeValueBackDelegate?


@IBOutlet weak var inputField: UITextField!
var firstObject: Object!
var secondObject: Object!

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

}

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

@IBAction func textFieldDidChange(textField: UITextField) {
    secondObject.someValue = textField.text!
    // Save the value in the delegate
    delegate?.writeValueBack(secondObject.someValue)
}


override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "TwoToThreeSegue" {
        let threeVC = segue.destinationViewController as! ThreeVC
        threeVC.firstObject = firstObject
        threeVC.secondObject = secondObject
    }
}
}