What happens when rangeOfCharacterFromSet is called?

Question

What this following code mean, I know this is to avoid typing characters other than numbers in a TextField. But what is actually happening behind this function rangeOfCharacterFromSet . What it will return.

if ([string rangeOfCharacterFromSet:[[NSCharacterSet decimalDigitCharacterSet] invertedSet]].location != NSNotFound)
        return NO;

In documentation it said

Finds and returns the range in the receiver of the first character from a given character set. The range in the receiver of the first character found from aSet. Returns a range of {NSNotFound, 0} if none of the characters in aSet are found

I can't even understand what is receiver And why NSNotFound is used here. And what is that aSet

Please explain me with some example for better understanding (Like what will happen when i press a character other than numbers)

score 2 · Accepted Answer · answered Jun 24 '16 at 10:22

- (void)test {
NSString *str = @"input content";
NSCharacterSet *characterSet = [NSCharacterSet decimalDigitCharacterSet];
NSRange range = [str rangeOfCharacterFromSet:characterSet];
NSLog(@"location:%ld, length:%ld", range.location, range.length);
// range.location is 9223372036854775807, in fact it is a NSNotFound which means not exists, range.length is 0

str = @"input 1";
range = [str rangeOfCharacterFromSet:characterSet];
NSLog(@"location:%ld, length:%ld", range.location, range.length);
// range.location is 6, range.length is 1

str = @"input 123";
range = [str rangeOfCharacterFromSet:characterSet];
NSLog(@"location:%ld, length:%ld", range.location, range.length);
// range.location is 6, range.length is 1

str = @"123 input 123";
range = [str rangeOfCharacterFromSet:characterSet];
NSLog(@"location:%ld, length:%ld", range.location, range.length);
// range.location is 0, range.length is 1
}

In the test, str is the receiver, when you call a method, who call who is reciever: [receiver callTheMethod]. Abount NSCharacterSet, I think the document explains clearly:

An NSCharacterSet object represents a set of Unicode-compliant characters. NSString and NSScanner objects use NSCharacterSet objects to group characters together for searching operations, so that they can find any of a particular set of characters during a search. The cluster’s two public classes, NSCharacterSet and NSMutableCharacterSet, declare the programmatic interface for static and dynamic character sets, respectively.

NSRange is the result of [str rangeOfCharacterFromSet:characterSet], it is a struct, range.location is the first index in str which is included in characterSet, it is a NSInteger type, when the str not exits a the content of characterSet it will be a very big integer, and it means NSNotFound. range.length means as the words, at here, it always is 1 unless range.location is NSNotFound.

Hope it helps.

score 2 · Answer 2 · answered Jun 24 '16 at 10:30

Well, let me say it with this words: If you do not know, what a receiver is, you should read a beginner's book about Objective-C.

However, …

The receiver is the object, you send the message to. So make it a bit easier to understand:

NSCharacterSet *digits = [NSCharacterSet decimalDigitCharacterSet];
[string rangeOfCharacterFromSet:digits];

In the first line you send the message decimalDigitCharacterSet to the class object of NSCharacterSet. In the second line you send the message rangeOfCharacterFromSet:digits to an instance object of NSString.

So let us translate the docs, step 1:

Finds and returns the range in the string (formerly: receiver) of the first character from a given character set. The range in the receiver of the first character found from aSet. Returns a range of {NSNotFound, 0} if none of the characters in aSet are found

Since a range contains two plain integers, you cannot assign nil to them to mark an error. It would be 0. Therefore a magic number (NSNotFound) is assigned. However, don't care about this, just check the length on 0.

The set is the character set, a set containing the digits.

score 0 · Answer 3 · answered Jun 24 '16 at 09:43

What the code does is it returns NO if the string contains a character that isn't a number.

If you call [myString rangeOfCharacterFromSet:mySet], myString is the receiver and mySet is the aSet.

NSNotFound is just an arbitrary constant that indicates that none of the characters in the set is found.

What happens when rangeOfCharacterFromSet is called?

3 Answers3