TextField Validation With Regular Expression

Question

I need help with code that looks at a textfield make sure it starts with either a (+ or -) then has 3 integers after it.

So valid data looks like +234 or -888

Answer 1

I am not sure how you'd like to handle user input and feedback. First I'll show a simple way to keep the user in the editing mode of the textField if her input is not valid.

First of all two delegate methods:

- (BOOL)textFieldShouldReturn:(UITextField *)aTextField
{
    [aTextField resignFirstResponder];
    return YES;
}

- (BOOL)textFieldShouldEndEditing:(UITextField *)aTextField
{
    return [self validateInputWithString:aTextField.text];
}

The testing method, which just returns YES or NO whether the input is valid or not:

- (BOOL)validateInputWithString:(NSString *)aString
{
    NSString * const regularExpression = @"^([+-]{1})([0-9]{3})$";
    NSError *error = NULL;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regularExpression
                                                                           options:NSRegularExpressionCaseInsensitive
                                                                             error:&error];
    if (error) {
        NSLog(@"error %@", error);
    }

    NSUInteger numberOfMatches = [regex numberOfMatchesInString:aString
                                                        options:0
                                                          range:NSMakeRange(0, [aString length])];
    return numberOfMatches > 0;
}

That's it. However I'd recommend showing some live status to the user whether his input is ok or not. Add the following notifcation, for example in your viewDidLoad method:

- (void)viewDidLoad
{
    // ...
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(validateInputCallback:) 
                                                 name:@"UITextFieldTextDidChangeNotification" 
                                               object:nil];
}

- (void)validateInputCallback:(id)sender
{
    if ([self validateInputWithString:textField.text]) {
        // For example turn a label green and let it say: "OK"
    } else {
        // For example turn a label red and let it say: "Allowed: + or minus followed by exactly three digits"
    }
}

Finally: If you need to access the capture groups (+ or - and the number) of the regular expression the following code will help:

// ... reg ex creation ...
NSArray *matches = [regex matchesInString:aString
                                  options:0
                                    range:NSMakeRange(0, [aString length])];

for (NSTextCheckingResult *match in matches) {
    for (int i = 0; i < [match numberOfRanges]; i++) {
        NSLog(@"range %d: %d %d", i, [match rangeAtIndex:i].location, [match rangeAtIndex:i].length);
        NSLog(@"substring %d: %@", i, [aString substringWithRange:[match rangeAtIndex:i]]);
    }
}

Answer 2

Use UIPickerView instead

I am departing from the question title but IMHO considering what you need, it may be better to use UIPickerView to have a "spinning-wheel" type of entry, like you do in the Clock app when setting alarm. It can start at "+000" and user can tumble some of the four wheels ([+-]. [0-9], [0-9], [0-9]) as needed

Answer 3

Implement the -textField:shouldChangeCharactersInRange:replacementString in your UITextFieldDelegate and use NSRegularExpression to validate the changes.

Answer 4

Validate Email id or Phone number using Regular Expression

Ddelegate methods:

- (BOOL)textFieldShouldReturn:(UITextField *)aTextField
{
    [aTextField resignFirstResponder];
    return YES;
}

- (BOOL)textFieldShouldEndEditing:(UITextField *)aTextField
{
    return [self validateEmail:aTextField.text]; // Change validateEmail to validatePhone for phone validation.
}

Returns YES or NO whether the input is valid or not:

- (BOOL) validateEmail: (NSString *) candidate {
    NSString *emailRegex = @"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}"; 
    NSPredicate *emailTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegex]; 

    return [emailTest evaluateWithObject:candidate];
}

- (BOOL) validatePhone: (NSString *) candidate {
    NSString *phoneRegex = @"^+(?:[0-9] ?){6,14}[0-9]$"; 
    NSPredicate *phoneTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", phoneRegex]; 

    return [phoneTest evaluateWithObject:candidate];
}