Restrict user to only entering one word in UITextField - objective-c

Question

Is there a way to only allow the user enter one word in the UITextField? If so, how?
Here's the current code that I'm using:
-(BOOL) textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
_disallowedCharacters = [NSCharacterSet whitespaceCharacterSet];
for(int i = 0; i < [_searchBox.text length]; i++){
unichar c = [_searchBox.text characterAtIndex:i];
if (![_disallowedCharacters characterIsMember:c])
{
return NO;
}
}
return YES;
}

Answer 1

Use the UITextFieldDelegate protocol:
- (BOOL) textField:(UITextField*)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString*)textEntered
{
for (int i = 0; i < [textEntered length]; i++)
{
unichar c = [textEntered characterAtIndex:i];
if ([disallowedCharacters characterIsMember:c])
{
return NO;
}
}
return YES;
}
where disallowedCharacters is an NSCharacterSet containing the characters that should not be accepted by the keyboard, i.e. a space, punctuation, numbers, etc:
self.disallowedCharacters = [NSCharacterSet characterSetWithCharactersInString:#" ,.123"];

Answer 2

For a character set (for Evan's answer) that checks against whitespace and newlines, you can use
self.disallowedCharacters = [NSCharacterSet whitespaceAndNewlineCharacterSet];
If you want to check against characters besides whitespace and newlines, create a mutableCopy and add whatever you'd like to it:
NSMutableCharacterSet *set = [[NSCharacterSet whitespaceAndNewlineCharacterSet] mutableCopy];
[set formUnionWithCharacterSet:[NSCharacterSet punctuationCharacterSet]];
[set formUnionWithCharacterSet:[NSCharacterSet symbolCharacterSet];
[set addCharactersInString:#"whatever you want"];
...
self.disallowedCharacters = [[set copy] autorelease];
[set release];
The NSCharacterSet docs have a good overview of the character sets available to you.