正文：
以一個簡單的例子來應用 UIPickerView

成果圖：

程式碼：

import UIKit

class ViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource {
    
    @IBOutlet weak var varLabel: UILabel!
    @IBOutlet weak var customPickerView: UIPickerView!
    
    let numbers = ["0","1","2","3","4","5"]
    var whatNumber = "0"
    
    override func viewDidLoad() {
        super.viewDidLoad()
        customPickerView.delegate = self
        customPickerView.dataSource = self
    }
    // MARK: - UIPickerViewDataSource 必須實作的方法：
    // UIPickerView 有幾列可以選擇
    func numberOfComponents(
        in pickerView: UIPickerView) -> Int {
        return 1
    }
    // UIPickerView 各列有多少行資料
    func pickerView(_ pickerView: UIPickerView,
        numberOfRowsInComponent component: Int) -> Int {
        return numbers.count
    }
    // MARK: -
    // UIPickerView 每個選項顯示的資料
    func pickerView(_ pickerView: UIPickerView,
        titleForRow row: Int, forComponent component: Int)
        -> String? {
        return numbers[row]
    }
    // UIPickerView 改變選擇後執行的動作
    func pickerView(_ pickerView: UIPickerView,
        didSelectRow row: Int, inComponent component: Int) {
        whatNumber = numbers[row]
        // 將改變的結果印出來
        print("選擇的是 \(whatNumber)")
        varLabel.text = "\(whatNumber)"
    }
}