如何在同一视图中将多个选择器视图与不同的数据源一起使用？

Question

我有一个视图，其中有三个选择器视图。两个选择器视图具有相同的数据，数组的编号为1到100。第三个选择器视图具有一个数组，其中包含模型铁轨制造商的列表。我已经使用在此站点上找到的方法标记了选择器视图，但是当我运行该应用程序时，所有三个选择器视图的数据都为1到100。我还将控件从所有选择器视图拖到视图顶部的黄色圆圈，然后单击
dataSource 和 委托 。如何在一个视图中使用具有不同数据源的多个选择器视图？另外，为了使代码运行，我不得不从所有 @IBOutlet中
删除 weak __与选择器视图有关的声明。 这是一件坏事吗？我对代码比较陌生。谢谢。

选择器视图场景屏幕截图

import UIKit

class ViewController: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate {
    //MARK: Properties

    @IBOutlet var layoutLengthPickerView: UIPickerView!
    @IBOutlet var layoutWidthPickerView: UIPickerView!
    @IBOutlet var trackPickerView: UIPickerView!

    override func viewDidLoad() {
        super.viewDidLoad()

        layoutLengthPickerView = UIPickerView()
        layoutWidthPickerView = UIPickerView()
        trackPickerView = UIPickerView()

        layoutLengthPickerView.tag = 0
        layoutWidthPickerView.tag = 1
        trackPickerView.tag = 2
    }

    let numbers = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "100"]

    let manufacturers = ["Atlas True Track", "Atlas Code 100", "Atlas Code 83", "Bachmann Nickel Silver", "Bachmann Steel Alloy", "Kato", "Life-Like Trains Code 100", "LIfe-Like Trains Power-Loc", "Peco Code 100", "Peco Code 83", "Peco Code 75", "Shinohara Code 100", "Shinohara Code 70", "Walthers"]

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

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        if pickerView.tag == 0 {
            return numbers[row]
        } else if pickerView.tag == 1 {
            return numbers[row]
        } else if pickerView.tag == 2 {
            return manufacturers[row]
        }

        return ""
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        if pickerView.tag == 0 {
            return numbers.count
        } else if pickerView.tag == 1 {
            return numbers.count
        } else if pickerView.tag == 2 {
            return manufacturers.count
        }
        return 1
    }
}

Answer 1

在处理具有委托人和数据源的多个控件时，应考虑通过为多个选择器的委托创建单独的对象来避免视图控制器膨胀（即，按照单一职责原则的精神）。这使得这个逻辑出视图控制器本身，并避免了单一繁琐UIPickerViewDataSource和UIPickerViewDelegate努力服务的多个采摘与毛茸茸的方法if-
else或switch语句。

例如，这是一个视图控制器，它具有两个拾取器的出口，但是您不必为视图控制器添加代码来管理dataSource和delegate为这些拾取器而烦恼，您可以为每个拾取器拥有单独的对象，并且所有视图控制器要做的就是说哪个委托对象将处理哪个选择器：

class ViewController: UIViewController {

    @IBOutlet weak var namePicker: UIPickerView!
    @IBOutlet weak var numberPicker: UIPickerView!

    let namePickerDelegate = NamePickerDelegate()
    let numberPickerDelegate = NumberPickerDelegate()

    override func viewDidLoad() {
        super.viewDidLoad()

        namePicker.delegate = namePickerDelegate
        namePicker.dataSource = namePickerDelegate

        numberPicker.delegate = numberPickerDelegate
        numberPicker.dataSource = numberPickerDelegate
    }

    @IBAction func didTapButton(_ sender: Any) {
        let nameValue = namePicker.selectedRow(inComponent: 0)
        let numberValue = numberPicker.selectedRow(inComponent: 0)

        print("\(nameValue); \(numberValue)")
    }

}

唯一的技巧是确保对这些委托对象保持强烈的引用，如上所示，因为按照最佳做法，选择器本身对引用的委托仅具有较弱的引用。

Picker委托方法的实现更加简洁：

class NamePickerDelegate: NSObject, UIPickerViewDataSource, UIPickerViewDelegate {
    let names = ["Mo", "Larry", "Curley"]

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

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

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

class NumberPickerDelegate: NSObject, UIPickerViewDataSource, UIPickerViewDelegate {
    let numbers: [String] = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .spellOut
        return (0 ..< 100).compactMap { formatter.string(for: $0) }  // use `flatMap` in Xcode versions prior to 9.3
    }()

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

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

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

现在，显然，这仍然是一个简化的示例，但是美丽之处在于，随着代码变得越来越复杂，详细信息被封装在单独的对象中，而不是将所有代码都包含在单个视图控制器中。

如果需要，可以让视图控制器为委托/数据源对象提供字符串列表。实际上，这简化了它，因为对于选择器委托只需要一个类，而对于每个选择器只需实例化一个不同的类：

class ViewController: UIViewController {

    let names = ["Mo", "Larry", "Curley"]

    let numbers: [String] = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .spellOut
        return (0 ..< 100).compactMap { formatter.string(for: $0) }  // use `flatMap` in Xcode versions prior to 9.3
    }()

    @IBOutlet weak var numberPickerOne: UIPickerView!
    @IBOutlet weak var numberPickerTwo: UIPickerView!
    @IBOutlet weak var namePicker: UIPickerView!

    lazy var numberPickerOneDelegate: PickerDelegate = PickerDelegate(strings: self.numbers)
    lazy var numberPickerTwoDelegate: PickerDelegate = PickerDelegate(strings: self.numbers)
    lazy var namePickerDelegate:PickerDelegate = PickerDelegate(strings: self.names)

    override func viewDidLoad() {
        super.viewDidLoad()

        numberPickerOne.delegate   = numberPickerOneDelegate
        numberPickerOne.dataSource = numberPickerOneDelegate

        numberPickerTwo.delegate   = numberPickerTwoDelegate
        numberPickerTwo.dataSource = numberPickerTwoDelegate

        namePicker.delegate        = namePickerDelegate
        namePicker.dataSource      = namePickerDelegate
    }

}

class PickerDelegate: NSObject, UIPickerViewDataSource, UIPickerViewDelegate {
    let strings: [String]

    init(strings: [String]) {
        self.strings = strings
        super.init()
    }

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

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

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