ios - 删除 UITextField 中的最后一个字符

Question

如果字符数超过 200，我将尝试删除 UITextField 中的最后一个字符。但它没有任何效果:

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
        print(textField.text?.characters.count)
        if (textField.text?.characters.count > 200){
            self.textField.shake()
            self.textField.becomeFirstResponder()
            self.textField.text?.characters.dropLast()
        }
        return true
    }

Answer 1

    func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool // return NO to not change text
{

    let textFieldString = textField.text! as NSString;

    var newString = textFieldString.stringByReplacingCharactersInRange(range, withString:string)

    if newString.characters.count > 200 {

// This will remove just last character, If u want to remove all the characters starting from 201st character pass 200 to substringToIndex method
        newString = newString.substringToIndex(newString.endIndex.advancedBy(-1))
        textField.text = newString

        return false
    }

   return true

}