iOS - UITextField 限制輸入

有時候使用輸入時, 想要限制輸入框只能輸入數字, 該如何實作呢？

我們可使用 NSCharacterSet 來達成此功能。

Step 1: 委託 UITextFieldDelegate

Step 2: 監聽輸入變化 shouldChangeCharactersInRange

Step 3: 設定限制字元

Source Code

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var numTextField: UITextField!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        numTextField.delegate = self;
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

extension ViewController : UITextFieldDelegate {
    func textField(textField: UITextField,
         shouldChangeCharactersInRange range: NSRange,
             replacementString string: String) -> Bool {
             let inverseSet = NSCharacterSet(charactersInString:"0123456789.").invertedSet
             let components = string.componentsSeparatedByCharactersInSet(inverseSet)
             let filtered = components.joinWithSeparator("")
             return string == filtered
    }
}