Swift：致命错误：在初始化 UIlabel 值时展开可选值时意外发现 nil

Question

我对 swift 很陌生（我通常使用 Java 和 C++ 编写代码），我正在构建我的第一个 ios 应用程序。 在这个应用程序中，我正在尝试创建一个选择器视图，问题是当我尝试将标签点的初始值设置为选择器视图（数组）中的第一项时，它会弹出错误

"致命错误：在展开 Optional 时意外发现 nil 价值”

这是我正在工作的代码

class ViewController: UIViewController, UIPickerViewDelegate{


    @IBOutlet var usertypeLabel: UILabel!
    @IBOutlet var Picker: UIPickerView!
    var usertype_array = ["patient","nurse"]
    //var usertype: String!
    override func viewDidLoad() {

        // Do any additional setup after loading the view, typically from a nib.
        super.viewDidLoad()
        usertypeLabel.text = usertype_array[0] //THIS IS WHERE THE ERROR OCCURS
    }

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

    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int{
        return 1
    }

    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int{
        return usertype_array.count
    }

    func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String!{
        return usertype_array[row]
    }

    func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int){
        var rowselected = usertype_array[row]
        usertypeLabel.text = rowselected        
    }
}

知道为什么会发生错误吗？请注意，如果我删除那行代码，它仍然会运行。谢谢。

Answer 1

您缺少UIPickerViewDataSource 并在此处添加：

class ViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource

并在您的 viewDidLoad 方法中添加：

Picker.dataSource = self
Picker.delegate = self

这是您的完整工作代码：

import UIKit

class ViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource{


    @IBOutlet var usertypeLabel: UILabel!
    @IBOutlet var Picker: UIPickerView!
    var usertype_array = ["patient","nurse"]
    //var usertype: String!
    override func viewDidLoad() {

        // Do any additional setup after loading the view, typically from a nib.
        super.viewDidLoad()
        Picker.dataSource = self
        Picker.delegate = self
        usertypeLabel.text = usertype_array[0] //THIS IS WHERE THE ERROR OCCURS
    }

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

    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int{
        return 1
    }

    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int{
        return usertype_array.count
    }

    func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String!{
        return usertype_array[row]
    }

    func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int){
        var rowselected = usertype_array[row]
        usertypeLabel.text = rowselected
    }
}

如果您的插座正确，它将正常工作。

查看THIS 示例了解更多信息。