我无法将数据从一个 VC 传递到另一个 [重复]

Question

我将数据从一个 VC 传递回第一个 VC。我正在使用此代码：

@IBAction func goBack(_ sender: Any) {
    dismiss(animated: true, completion: nil)
    print(self.entryField.text!)
    performSegue(withIdentifier: "sendText", sender: self)
 }

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let destVC = segue.destination as! ViewController
    let printName = self.entryField.text!
    print(self.entryField.text!)
    destVC.nameToDisplay=printName
}

这是我的数据所在VC的代码。

我想在其中显示我的结果的 VC 的代码。

var nameToDisplay = ""

override func viewWillAppear(_ animated: Bool) {
    titleDisplay.text=nameToDisplay
}

我无法传递数据，我尝试打印nameToDisplay，但它给出了空字符串。

Answer 1

将值从第二个控制器传回第一个控制器的合理模式可能是这样的：

class FirstViewController: UIViewController {
    //......

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let secondViewController = segue.destination as? SecondViewController {
            secondViewController.nameHandler = { (name) -> Void in
                titleDisplay.text=nameToDisplay //second controller will call back here to pass the name value when it's going back.
            }
        }
    }

    //......
}

class SecondViewController: UIViewController {
    //......

    var nameHandler:((_ name:String)->Void)? //a closure to call back name

    @IBAction func goBack(_ sender: Any) {
        if let name = self.entryField.text {
            self.nameHandler?(name) //call back and pass the name to the first controller
        }
        dismiss(animated: true, completion: nil)
    }

    //......
}

Answer 2

您正在寻找视图控制器之间的一对一通信。这可以通过 iOS 中的不同方式来实现。

1- 委托

2- 块，闭包。

上述解决方案是使用块。我会和代表们一起告诉你

class FirstVC: UIViewController, PassData {
func pushVC() {
    let secondVC = SecondVC()
    secondVC.delegate = self
    self.navigationController?.pushViewController(secondVC, animated: true)
}

func passDataOnDismiss(data: String) {
    print(data)
}}

protocol PassData: class {
func passDataOnDismiss(data: String)
}

class SecondVC: UIViewController {
    weak var delegate: PassData?
    @IBAction func didButtonPress() {
        self.delegate?.passDataOnDismiss(data: "I am passing this string back to First VC")
        self.navigationController?.popViewController(animated: true)
    }
}