Swift - Getting Only Alphanumeric Characters from String

Swift - Getting only AlphaNumeric Characters from String

You may directly use replacingOccurrences (that removes all non-overlapping matches from the input string) with [^A-Za-z0-9]+ pattern:

let str = "_<$abc$>_"
let pattern = "[^A-Za-z0-9]+"
let result = str.replacingOccurrences(of: pattern, with: "", options: [.regularExpression])
print(result) // => abc

The [^A-Za-z0-9]+ pattern is a negated character class that matches any char but the ones defined in the class, one or more occurrences (due to + quantifier).

See the regex demo.

Remove all non-numeric characters from a string in swift

I was hoping there would be something like stringFromCharactersInSet() which would allow me to specify only valid characters to keep.

You can either use trimmingCharacters with the inverted character set to remove characters from the start or the end of the string. In Swift 3 and later:

let result = string.trimmingCharacters(in: CharacterSet(charactersIn: "0123456789.").inverted)

Or, if you want to remove non-numeric characters anywhere in the string (not just the start or end), you can filter the characters, e.g. in Swift 4.2.1:

let result = string.filter("0123456789.".contains)

Or, if you want to remove characters from a CharacterSet from anywhere in the string, use:

let result = String(string.unicodeScalars.filter(CharacterSet.whitespaces.inverted.contains))

Or, if you want to only match valid strings of a certain format (e.g. ####.##), you could use regular expression. For example:

if let range = string.range(of: #"\d+(\.\d*)?"#, options: .regularExpression) {
    let result = string[range] // or `String(string[range])` if you need `String`
}

The behavior of these different approaches differ slightly so it just depends on precisely what you're trying to do. Include or exclude the decimal point if you want decimal numbers, or just integers. There are lots of ways to accomplish this.

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For older, Swift 2 syntax, see previous revision of this answer.

Check if a String is alphanumeric in Swift

extension String {
    var isAlphanumeric: Bool {
        return !isEmpty && range(of: "[^a-zA-Z0-9]", options: .regularExpression) == nil
    }
}

"".isAlphanumeric        // false
"abc".isAlphanumeric     // true
"123".isAlphanumeric     // true
"ABC123".isAlphanumeric  // true
"iOS 9".isAlphanumeric   // false

Strip Non-Alphanumeric Characters from an NSString

We can do this by splitting and then joining. Requires OS X 10.5+ for the componentsSeparatedByCharactersInSet:

NSCharacterSet *charactersToRemove = [[NSCharacterSet alphanumericCharacterSet] invertedSet];
NSString *strippedReplacement = [[someString componentsSeparatedByCharactersInSet:charactersToRemove] componentsJoinedByString:@""];

Allow only alphanumeric characters for a UITextField

Use the UITextFieldDelegate method -textField:shouldChangeCharactersInRange:replacementString: with an NSCharacterSet containing the inverse of the characters you want to allow. For example:

// in -init, -initWithNibName:bundle:, or similar
NSCharacterSet *blockedCharacters = [[[NSCharacterSet alphanumericCharacterSet] invertedSet] retain];

- (BOOL)textField:(UITextField *)field shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)characters
{
    return ([characters rangeOfCharacterFromSet:blockedCharacters].location == NSNotFound);
}

// in -dealloc
[blockedCharacters release];

Note that you’ll need to declare that your class implements the protocol (i.e. @interface MyClass : SomeSuperclass <UITextFieldDelegate>) and set the text field’s delegate to the instance of your class.

Test UITextField text string to only contain alphanumeric characters

Check if the inversion of your accepted set is present:

if username.text!.rangeOfCharacterFromSet(letters.invertedSet) != nil {
    print("invalid")
}

letters should probably be alphanumericCharacterSet() if you want to include numbers as well.

If you want to accept underscores or more chars, you will probably have to create a character set by your own. But the inversion logic will stay the same.

Swift: Regex for allowing alphanumeric with one mandatory numeral

You can limit the number of alphanumeric in a string using the pattern [a-zA-Z0-9] and limit the minimum and maximum occurrences using {8,13}. You can also make sure there is at least one digit doing a positive lookahead pattern for digits (?=.*\\d) and non digits (?=.*\\D):

let regex = "^(?=.*\\d)(?=.*\\D)([a-zA-Z0-9]{8,13})$"

Regex details

^ asserts position at start of the string

(?=.*\d) • Positive lookahead that matches any character that's a
digit

(?=.*\D) • Positive lookahead that matches any character thats a
non-digit

([a-zA-Z0-9]) • First capturing group that matches any alphanumeric character

{8,13} • limits occurrences of the preciding token (from 8 to 13)

$ asserts position at end of the string

let string = "abcdefg1"

if let range = string.range(of: regex, options: .regularExpression) {
    print(string[range])  // abcdefg1\n"
}

Allow only alpha numeric characters in UITextView

You can achieve that using [[[NSCharacterSet alphanumericCharacterSet] invertedSet]. This method will return a character set containing only characters that don’t exist in the receiver.

NSCharacterSet *charactersToBlock = [[NSCharacterSet alphanumericCharacterSet] invertedSet];

//Conform UITextField delegate and implement this method.

 - (BOOL)textField:(UITextField *)field shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)characters
 {
    return ([characters rangeOfCharacterFromSet:charactersToBlock].location == NSNotFound);
 }

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