iPhone: regular expression and text input validation in UITextField is failing

I have the following code thats supposed to take the input entered into a UITextField and validate it. It doesn't seem to be working and Im a little confused as to why.

Could someone give me some advice please?

NSString *const regularExpression = @"([0-9a-zA-Z\\s]{1,6})";
NSError *error = NULL;
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regularExpression options:NSRegularExpressionCaseInsensitive error:&error];

           if (error) 
              {
               NSLog(@"error %@", error);
              }

NSUInteger numberOfMatches = 
[regex numberOfMatchesInString:s                                   options:0                                                 range:NSMakeRange(0, [s length])];
NSLog(@"index = %d", i);
NSLog(@"Value of TextField = %@", s);
NSLog(@"Regular expression is = %@", regularExpression);
if (numberOfMatches <= 0)
  {
   NSLog(@"Failed regex test ");
  }

This string should fail the regular expression test :"Einxnkxkd Xnckck"

But it passed.

im not sure how and why... A开发者_如何学Pythonnything obvious Im missing here? Thanks

The method numberOfMatchesInString: searches for matches within the string. It does not test your pattern against the entire string.

It is passing because the pattern ([0-9a-zA-Z\\s]{1,6}) is matching at least the first six letters of your test string Einxnkxkd Xnckck yielding Einxnk. In fact, I can find lots of matches: E, Ein, inx, etc.

If you want to make sure the whole string matches the pattern, use ^ to indicate the beginning of the string and $ to mark the end of it, so that your pattern becomes ^([0-9a-zA-Z\\s]{1,6})$.

If you want to limit the expression to exactly the string, you need to wrap the expression in ^..$:

NSString *const regularExpression = @"^([0-9a-zA-Z\\s]{1,6})$";

Edit: Use the RegEx Air app to test, it's pretty handy (or any other reg exp tester)