限制 UITextField 中的字符？ - 斯威夫特/Xcode

Question

I'm new to developing and I am trying to limit the number of characters that can be entered in a textfield, with the most recent version of Swift. I have tried to follow several different tutorials and have checked out a few different answers around the site, but I am not having much luck.

Currently, I have this entered in my swift file:

@IBAction func InfoTextFieldLimit(sender: UITextField) {

        self.InfoTextField.delegate = self

        func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {

            let currentCharacterCount = textField.text?.characters.count ?? 0
            if (range.length + range.location > currentCharacterCount) {

                return false
            }

            let newLength = currentCharacterCount + string.characters.count - range.length
            return newLength <= 10
        }
    }

...I'm not getting any errors, but nothing seems to be happening when I run the app.

I have also tried at least 3 other methods that I didn't bother copying. (but can provide on request)

Can anybody tell me what I'm doing wrong and point me in the right direction? Would be much appreciated! ...I feel like there's a good chance I might be overlooking something that's obvious.

I am also going to want to do this with a textview down the road, how would that be different?

Answer 1

func textField(textField: UITextField, shouldChangeCharactersInRange range:      NSRange, replacementString string: String) -> Bool {
    let maxLength = 50
    guard let text = textField.text else { return true }     
    let newLength = text.characters.count + string.characters.count - range.length
    return newLength <= maxLength
}

Also make sure you have set the delegate of the UITextField to the UIViewController

Answer 2

I originally had this code in objective-c:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    NSUInteger newLength = [textField.text length] + [string length] - range.length;
    return (newLength > 4) ? NO : YES;
}

I tried converting it to swift, let me know if it works... You have to use the UITextFieldDelegate method.

func textField( textField:UITextField,shouldChangeCharactersInRange range:NSRange,replacementString string:NSString)->Bool{
var newLength:NSUInteger = textField.text.length + string.length  - range.length 

return null(newLength >  4 )?false:true

}

Answer 3

Just in case, don't forget to guard range size before applying it to the string. Otherwise, you will get crash if the user will do this:

Type maximum length text Insert something (Nothing will be inserted due to length limitation, but iOS doesn't know about it) Undo insertion (You get crash, cause range will be greater than actual string size)

Also, using iOS 13 users can accidentally trigger this by gestures

I suggest you add to your project this

extension String {
    func replace(with text: String, in range: NSRange) -> String? {
        guard range.location + range.length <= self.count else { return nil }
        return (self as NSString).replacingCharacters(in: range, with: text)
    }
}

And use it like this:

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    guard let newText = textView.text.replace(with: text, in: range) else { return false }
    return newText.count < maxNumberOfCharacters
}

Otherwise, you will constantly be getting crashed in your app

maxNumberOfCharacters - your constant or @IBInspectable variable