UITextField Should accept number only values

I've implemented the snippet which has the features for textField:

1. Check the maximum allowed characters.
2. Check the valid decimal number.
3. Check only numeric numbers.

The code is the UITextField delegate method. Before you use this snippet, you must have these properties:

1. self.maxCharacters
2. self.numeric // Only int characters.
3. self.decimalNumeric // Only numbers and ".", "," (for specific locales, like Russian).

Code:

- (BOOL)textField:(UITextField *) textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if(self.numeric || self.decimalNumeric)
    {
        NSString *fulltext = [textField.text stringByAppendingString:string];
        NSString *charactersSetString = @"0123456789";

        // For decimal keyboard, allow "dot" and "comma" characters.
        if(self.decimalNumeric) {
            charactersSetString = [charactersSetString stringByAppendingString:@".,"];
        }

        NSCharacterSet *numbersOnly = [NSCharacterSet characterSetWithCharactersInString:charactersSetString];
        NSCharacterSet *characterSetFromTextField = [NSCharacterSet characterSetWithCharactersInString:fulltext];

        // If typed character is out of Set, ignore it.
        BOOL stringIsValid = [numbersOnly isSupersetOfSet:characterSetFromTextField];
        if(!stringIsValid) {
            return NO;
        }

        if(self.decimalNumeric)
        {
            NSString *currentText = [textField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

            // Change the "," (appears in other locale keyboards, such as russian) key ot "."
            currentText = [currentText stringByReplacingOccurrencesOfString:@"," withString:@"."];

            // Check the statements of decimal value.
            if([fulltext isEqualToString:@"."]) {
                textField.text = @"0.";
                return NO;
            }

            if([fulltext rangeOfString:@".."].location != NSNotFound) {
                textField.text = [fulltext stringByReplacingOccurrencesOfString:@".." withString:@"."];
                return NO;
            }

            // If second dot is typed, ignore it.
            NSArray *dots = [fulltext componentsSeparatedByString:@"."];
            if(dots.count > 2) {
                textField.text = currentText;
                return NO;
            }

            // If first character is zero and second character is > 0, replace first with second. 05 => 5;
            if(fulltext.length == 2) {
                if([[fulltext substringToIndex:1] isEqualToString:@"0"] && ![fulltext isEqualToString:@"0."]) {
                    textField.text = [fulltext substringWithRange:NSMakeRange(1, 1)];
                    return NO;
                }
            }
        }
    }

    // Check the max characters typed.
    NSUInteger oldLength = [textField.text length];
    NSUInteger replacementLength = [string length];
    NSUInteger rangeLength = range.length;

    NSUInteger newLength = oldLength - rangeLength + replacementLength;
    BOOL returnKey = [string rangeOfString: @"\n"].location != NSNotFound;

    return newLength <= _maxCharacters || returnKey;
}

Demo:

In whatever UITextField you're getting these values from, you can specify the kind of keyboard you want to appear when somebody touches inside the text field.

E.G. a numeric-only keyboard.

Like this screenshot:

This is easily set when working with the XIB and the Interface Builder built into Xcode, but if you want to understand this programmatically, take a look at Apple's UITextInputTraits protocol reference page, specifically the keyboardType property information.

To filter out punctuations, set the textfield's delegate and set up the shouldChangeCharactersInRange method:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    NSCharacterSet *numbersOnly = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
    NSCharacterSet *characterSetFromTextField = [NSCharacterSet characterSetWithCharactersInString:textField.text];

    BOOL stringIsValid = [numbersOnly isSupersetOfSet:characterSetFromTextField];
    return stringIsValid;
}

[textField setKeyboardType:UIKeyboardTypeNumberPad];

Objective C

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (!string.length) 
        return YES;

    if (textField == self.tmpTextField)
    {
        NSString *newString = [textField.text stringByReplacingCharactersInRange:range withString:string];
        NSString *expression = @"^([0-9]+)?(\\.([0-9]{1,2})?)?$";
        NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:expression 
                                                                               options:NSRegularExpressionCaseInsensitive 
                                                                                 error:nil];
        NSUInteger numberOfMatches = [regex numberOfMatchesInString:newString
                                                            options:0
                                                              range:NSMakeRange(0, [newString length])];        
        if (numberOfMatches == 0)
            return NO;        
    }
    return YES;
}

Swift 3.0

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    if !string.characters.count {
        return true
    }
    do {
        if textField == self.tmpTextField {
            var newString = textField.text.replacingCharacters(inRange: range, with: string)
            var expression = "^([0-9]+)?(\\.([0-9]{1,2})?)?$"
            var regex = try NSRegularExpression(pattern: expression, options: NSRegularExpressionCaseInsensitive)
            var numberOfMatches = regex.numberOfMatches(inString: newString, options: [], range: NSRange(location: 0, length: newString.characters.count))
            if numberOfMatches == 0 {
                return false
            }
        }
    }
    catch let error {
    }
    return true
}