ios - 无法从其他类设置 UITextfield 的文本

Question

我正在尝试使用以下代码为 FirstViewController 的 SecondViewController 中的 UITextField 设置文本:

// First ViewController
@IBAction func buttonAction(_ sender: Any) {
    let viewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "SecondViewController") as? SecondViewController
    viewController?.sampleTxtField?.text = "world"
    if let navigator = self.navigationController {
        navigator.pushViewController(viewController!, animated: true)
    }
}

// Second ViewController
 @IBOutlet weak var sampleTxtField: UITextField?
override func viewDidLoad() {
    super.viewDidLoad()
    print("the textfield value is,\(String(describing: sampleTxtField?.text))")
}

在我得到的日志中:"the textfield value is,Optional("")"

我想我犯了一些愚蠢的错误。我检查了很多问题，但找不到任何解决方案。

Answer 1

您的代码有误。

let viewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "SecondViewController") as? SecondViewController
    viewController?.sampleTxtField?.text = "world"

在上面的声明中， View 没有在 UI 中加载，所以 sampleTxtField 总是为 nil，而是在 SecondVC 中创建一个属性，var sample : String? 并将其分配为多于。然后在SecondVC的viewDidload中，赋值为textField.text = sample

// First ViewController

@IBAction func buttonAction(_ sender: Any) {
    let viewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "SecondViewController") as? SecondViewController
    viewController?.sample = "world"
    if let navigator = self.navigationController {
        navigator.pushViewController(viewController!, animated: true)
    }
}

//第二个 View Controller

@IBOutlet weak var sampleTxtField: UITextField?
var sample : String?
override func viewDidLoad() {
    super.viewDidLoad()
sampleTxtField.text =  sample
    print("the textfield value is,\(String(describing: sampleTxtField?.text))")
}