How to enter Numbers only in UITextField and limit maximum length?

Question

In UITextField we Enter Numeric only and limit up to 3 numeric for this i used below code

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string  {


    NSUInteger newLength = [textField.text length] + [string length] - range.length;

    NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:NUMBERS_ONLY] invertedSet];

    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];

    while (newLength < CHARACTER_LIMIT) {
        return [string isEqualToString:filtered];
    }

/* Limits the no of characters to be enter in text field */

    return (newLength > CHARACTER_LIMIT ) ? NO : YES; 

}

When i press long press on textfield (like below image )and enter string between two numbers it's allowing all special characters and charterers also.

Answer 1

Not that I don't like the answer I wrote at this question, that was copy & pasted here also. I'll try to explain your error.

This answer is based on the assumption that your constants are defined something like this:

#define NUMBERS_ONLY @"1234567890"
#define CHARACTER_LIMIT 3

The reason your logic is failing is that you never handle the event when newLength will be equal to the CHARACTER_LIMIT.

To illustrate suppose your textfield is empty and you request to paste the string @"ABC" to the textfield, your delegate method is called. You create the string filtered which correctly evaluates to an empty string, and you can't wait to execute the line return [string isEqualToString:filtered]; but you never actually evaluate that line because you don't meet the entry requirements for the while loop, because newLength is 3. so the simple return (newLength > CHARACTER_LIMIT ) ? NO : YES; decides the return value.

If your CHARACTER_LIMIT is actually 4 for some reason, just imagine @"ABCD" as the string the logic still applies.

Here is a simple example of your function corrected to work. Again I'm assuming that CHARACTER_LIMIT is equal to 3.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string  {
    NSUInteger newLength = [textField.text length] + [string length] - range.length;
    NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:NUMBERS_ONLY] invertedSet];
    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];
    return (([string isEqualToString:filtered])&&(newLength <= CHARACTER_LIMIT));
}