How to Input Dash After Every 4th Character in Objective-C

Question

I have a UITextField that gets a credit card input. How can I automatically insert a dash after the user inputs a 4th character just like how the Groupon app for iOS does it when a user is typing his credit card number? Thanks in advance.

Answer 1

This was harder that i thought.A common notification sent when the text changes is UITextFieldTextDidChangeNotification. In the viewDidLoad method you should register to receiver this notification and perform a selector when the text changes.In the selector you add a dash every 4 characters.
In my code the textfield is named textField.

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSNotificationCenter* center=[NSNotificationCenter defaultCenter];
    [center addObserver: self selector: @selector(textDidChange:) name: UITextFieldTextDidChangeNotification object: textField];
}

- (void) textDidChange : (NSNotification*) notification
{
    NSString* string=[[textField text] stringByReplacingOccurrencesOfString: @"-" withString: @""];
    __block NSMutableString* newString= [string mutableCopy];
    NSMutableIndexSet* set=[NSMutableIndexSet new];
    for(NSUInteger i=4; i<[string length];i+=4)
    {
        [set addIndex: i+i/4-1];
    }
    [set enumerateIndexesInRange: NSMakeRange(0, [string length]+[string length]/4) options: 0 usingBlock: ^(NSUInteger index, BOOL* stop)
    {
        [newString insertString: @"-" atIndex: index];
    }];
    [textField setText: newString];
}

The code to add a dash every 4 characters is long, maybe there's a shorter way to do it.

PS: The last version was incorrect, I edited it (wasn't able to delete characters properly).

Answer 2

This has worked excellently for me:

iOS automatically add hyphen in text field

Check the answer by "dingo sky".