Ios 在展开可选值uitextfield时意外发现nil

我知道这里有很多意想不到的零值问题，但我尝试过其他方法，它们对我不起作用。底部的函数是从另一个视图控制器上的按钮调用的。基本上，问题是这段代码按预期工作，表单元素将DatePicker作为输入视图，并且在值更改时更新startDatePickerField.text，因此我知道startDatePickerField.text在屏幕上显示时不是空的。但是，当从包含我们正在使用的视图控制器的另一个视图控制器调用testForValidity（）函数时，我得到“在展开选项值错误时意外发现nil”。所有插座都连接正确，所以我知道不是这样

class popoverTableViewController: UITableViewController, UIPickerViewDelegate, UIPickerViewDataSource {

@IBOutlet var startDatePickerField: UITextField!

override func viewDidLoad() {
let startDatePicker:UIDatePicker = UIDatePicker()
    startDatePicker.datePickerMode = UIDatePickerMode.dateAndTime
    startDatePickerField.inputView = startDatePicker
    startDatePicker.minuteInterval = 5
    startDatePicker.addTarget(self, action:  #selector(popoverTableViewController.startDatePickerValueChanged(_:)), for: UIControlEvents.valueChanged) 
}

    @IBAction func startDateDidBegin(_ sender: AnyObject) {
}

    func startDatePickerValueChanged(_ sender: UIDatePicker) {

    let dateFormatter = DateFormatter()
    dateFormatter.dateStyle = DateFormatter.Style.long
    dateFormatter.timeStyle = DateFormatter.Style.short
    startDatePickerField.text = dateFormatter.string(from: sender.date)
    finishDateTime = sender.date

}

以及显示错误的函数：

    func testForValidity() {

    print(startDatePickerField.text)

}

---

在顶部，添加

UITextFieldDelegate

，使其成为：

class popoverTableViewController: UITableViewController, UIPickerViewDelegate, UIPickerViewDataSource, UITextFieldDelegate { 

然后在

viewDidLoad（）中添加此行：

self.startDatePickerField.delegate = self

在顶部，添加
UITextFieldDelegate
，使其成为：

class popoverTableViewController: UITableViewController, UIPickerViewDelegate, UIPickerViewDataSource, UITextFieldDelegate { 

然后在
viewDidLoad（）中添加此行：

self.startDatePickerField.delegate = self

问题：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}


您正试图通过实例方法从另一个类访问IBOutlet属性
nil值背后的原因是，当加载nib时，出口被初始化

因此，在您的情况下，当您在另一个视图控制器中时，您无法访问Outlet变量，否则您将始终得到nil

解决方案：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}

如果我假设正确，您希望在视图控制器中包含值后使用该值

最好的方法是遵循“设计模式”。i、 例如，您必须将所需的值存储在模型类中，并通过模型类实例访问该值

苹果有很好的文档。请通过。

Swift中的示例代码：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}

输出：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}

问题：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}


您正试图通过实例方法从另一个类访问IBOutlet属性
nil值背后的原因是，当加载nib时，出口被初始化

因此，在您的情况下，当您在另一个视图控制器中时，您无法访问Outlet变量，否则您将始终得到nil

解决方案：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}

如果我假设正确，您希望在视图控制器中包含值后使用该值

最好的方法是遵循“设计模式”。i、 例如，您必须将所需的值存储在模型类中，并通过模型类实例访问该值

苹果有很好的文档。请通过。

Swift中的示例代码：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}

输出：

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var outputLabel : UILabel!
    @IBOutlet weak var textField : UITextField!

    override func viewDidLoad() { super.viewDidLoad(); setupTextField() }

    func testValidity() -> (textFieldValue: UITextField?, modelValue: String?) {
        return (textField, TextFieldModel.sharedModel.textFieldData)
    }

    //MARK: - Text Field Delegates
    func textFieldShouldReturn(textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        outputLabel.text = textField.text
        TextFieldModel.sharedModel.textFieldData = textField.text
        return true
    }

}

class TextFieldModel {
    static let sharedModel = TextFieldModel()
    var textFieldData: String?
}

class DemoController: UIViewController {

    @IBOutlet weak var textFieldOutput: UILabel!
    @IBOutlet weak var modelOutput: UILabel!

    override func viewDidLoad() { super.viewDidLoad(); testValues() }

    func testValues() {
        let tvc = TextFieldViewController()
        textFieldOutput.text =  "Value of Text field is " + (tvc.testValidity().textFieldValue?.text ?? "nil")
        modelOutput.text = "Value accessed from Model Class is \(tvc.testValidity().modelValue)"
    }
}


extension TextFieldViewController {
    func setupTextField() {
        textField.placeholder = ""
        textField.delegate = self
        textField.becomeFirstResponder()
        textField.keyboardType = UIKeyboardType.Default
        textField.returnKeyType = UIReturnKeyType.Done

    }
}

testForValidity（）在哪里？在popoverTableViewController中？如何调用它？testForValidity（）在popoverTableViewController中是的，它是在按下按钮后从另一个类进行的简单调用。我意识到这个方法调用了我的popoverTableViewController的一个新实例，这就是我出错的原因。我认为修复与NSNotificationCenter有关，但我不确定如何实现它。testForValidity（）在哪里？在popoverTableViewController中？如何调用它？testForValidity（）在popoverTableViewController中是的，它是在按下按钮后从另一个类进行的简单调用。我意识到这个方法调用了我的popoverTableViewController的一个新实例，这就是我出错的原因。我认为修复与NSNotificationCenter有关，但我不确定如何实现它。非常感谢您花时间回答，非常有魅力！不客气。很高兴我能帮你解决问题。非常感谢你花时间回答，真有魅力！不客气。很高兴我能帮你解决问题。