I'm using NSScanner to restrict a text field's value to numbers only, but I want to allow "-" - objective-c

Question

I have an NSScanner in a custom NSNumberFormatter that scans for non-int values but I want it to skip "-" (dash)
- (BOOL)isPartialStringValid:(NSString *)partialString newEditingString:(NSString **)newString errorDescription:(NSString **)error {
if ([partialString length] == 0) {
return YES;
}
NSScanner *scanner = [NSScanner scannerWithString:partialString];
if (!([scanner scanInt:0] && [scanner isAtEnd])) {
return NO;
}
return YES;
}
I thought I had to use [scanner charactersToBeSkipped] but I don't know how that works

Answer 1

I came up with my own solution. Each time a character is typed, it checks if the first one is a dash. If it is, it skips the first character and checks if the rest of the string contains ints. If the first character is not a dash, it scans the whole string for ints.
- (BOOL)isPartialStringValid:(NSString *)partialString newEditingString:(NSString **)newString errorDescription:(NSString **)error {
if ([partialString length] == 0) {
return YES;
}
NSString *stringFromSecondChar;
NSString *firstChar = [partialString substringToIndex:1];
if ([partialString length] > 1 && [firstChar isEqualToString:#"-"]) {
stringFromSecondChar = [partialString substringFromIndex:1];
}
else {
stringFromSecondChar = partialString;
}
NSScanner *scanner = [NSScanner scannerWithString:stringFromSecondChar];
if ([partialString length] == 1 && [firstChar isEqualToString:#"-"]) {
return YES;
}
else if ([partialString length] >= 1 && [stringFromSecondChar containsString:#"-"]) {
return NO;
}
if ([firstChar isEqualToString:#"-"]) {
if (!([scanner scanInt:0] && [scanner isAtEnd])) {
return NO;
}
else {
return YES;
}
}
if (!([scanner scanInt:0] && [scanner isAtEnd])) {
return NO;
}
return YES;
}

Answer 2

Solution with regular expression:
- (BOOL)isPartialStringValid:(NSString *)partialString newEditingString:(NSString **)newString errorDescription:(NSString **)error {
if (partialString.length == 0)
return YES;
NSRange range = [partialString rangeOfString:#"^[-]?\\d*$" options:NSRegularExpressionSearch];
return (range.location != NSNotFound);
}
Solution with NSScanner:
- (BOOL)isPartialStringValid:(NSString *)partialString newEditingString:(NSString **)newString errorDescription:(NSString **)error {
if (partialString.length == 0 || [partialString isEqualToString:#"-"])
return YES;
NSScanner *scanner = [NSScanner scannerWithString:partialString];
return ([scanner scanInt:NULL] && [scanner isAtEnd]);
}