问在swift中输入所有UITextFields中的文本之前，如何禁用按钮？

EN

class ViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var textField: UITextField!
    @IBOutlet weak var button: UIButton!

    //Need to have the ViewController extend UITextFieldDelegate for using this feature
    func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {

        // Find out what the text field will be after adding the current edit
        let text = (textField.text as NSString).stringByReplacingCharactersInRange(range, withString: string)

        if !text.isEmpty{//Checking if the input field is not empty
            button.userInteractionEnabled = true //Enabling the button
        } else {
            button.userInteractionEnabled = false //Disabling the button
        }

        // Return true so the text field will be changed
        return true
    }

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

        //Setting the Delegate for the TextField
        textField.delegate = self
        //Default checking and disabling of the Button
        if textField.text.isEmpty{
            button.userInteractionEnabled = false // Disabling the button
        }
    }
}