swift - 从用户输入刷新 UIPicker

Question

我是 Xcode/Swift 新手，正在处理一项需要帮助的作业。我有一个简单的程序，启动时会显示名称列表。我想从 UITextField 中获取一个新名称，并将其添加到当前所选项目之后的选择器数据中。新添加的名称应在选择器中显示为所选项目(因此之前选择的项目将在此时选择器显示屏上紧邻其上方)。到目前为止，我的程序正在运行，但是，我的“picker.reloadAllComponents()”函数似乎破坏了某些东西。当我将其保留在适当位置时，选择器中不会显示任何数据。当我删除它时，我不知道我的 insertButton 操作是否有效。在哪里可以刷新选取器数据，以便在模拟器中看到选取器数据？谢谢。

import UIKit

class ViewController: UIViewController,
    UIPickerViewDelegate, UIPickerViewDataSource {

    var characterNames = [
        "Luke", "Leia", "Han", "Chewbacca", "Artoo",
        "Threepio", "Lando"]


    @IBOutlet weak var userInput: UITextField!
    @IBOutlet weak var picker: UIPickerView!

    @IBAction func selectButton(_ sender: UIButton) {
        let row = picker.selectedRow(inComponent: 0)
        let selected = characterNames[row]
        let title = "You selected \(selected)!"

        let alert = UIAlertController(
            title: title,
            message: "Thank you for choosing",
            preferredStyle: .alert)
        let action = UIAlertAction(
            title: "You're welcome",
            style: .default,
            handler: nil)
        alert.addAction(action)
        present(alert, animated: true, completion: nil)
    }


    @IBAction func insertButton(_ sender: UIButton) {
        characterNames.insert(userInput.text!, at: picker.selectedRow(inComponent: 0))
    }

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

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

    // MARK:-
    // MARK: Picker Data Source Methods

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    func pickerView(_ pickerView: UIPickerView,
                    numberOfRowsInComponent component: Int) -> Int {
        return characterNames.count
    }

    // MARK: Picker Delegate Methods
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        picker.reloadAllComponents()
        return characterNames[row]
    }
}

Answer 1

不要从 titleRorRow 方法中调用 picker.reloadAllComponents()，因为我认为这可能会调用无限循环 - 此委托(delegate)方法应该返回以下标题:仅该行，因为您的第二行运行正确。因此，将其从那里删除。

相反，在更新源代码后将其放入 insertButton 方法中。这将导致重新加载数据，并再次调用数据源方法来重新填充选取器。

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


@IBAction func insertButton(_ sender: UIButton) {
    characterNames.insert(userInput.text!, at: picker.selectedRow(inComponent: 0))
    picker.reloadAllComponents()
}