理解 Reactive 编程思想

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var textField: UITextField!
    override func viewDidLoad() {
        super.viewDidLoad()
        
        textField.delegate = self
        
        let stringArray = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
        let even = stringArray.map { Int($0)!
            }.filter {
                $0 % 2 == 0
        }
        print(even)
    }
}

extension UIViewController: UITextFieldDelegate {
    //在每次用户按下键盘，字母在屏幕上显示出来之前被调用
    public func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
        // 1. 每次的输入转换成一个整数
        if let n = Int(string) {
            // 2. 判断是否能够被2整除
            if n % 2 == 0 {
                print(n)
            }
        }
        return true
    }
}

资料来源：理解Reactive编程思想