UITextField input mask?

Question

http://sublime.nyasha.me/admin/form_masks.html

I use this technique to achieve nice results with html/css/java etc, but how does one achieve this in objective-c?

I've read so far about number formatting, but how can I literally have it so when the content is editable it displays the formatted version as they're typing and doesn't allow them to exceed .length in certain areas.

My example I need to use it for is

00:00:00 or 00h:00m:00s so when edited it will achieve __:__:__ or __h:__m:__s I've been scraping through the interwebs and cannot find such a technique, so far I've considered programatically doing something like this..

3x UITextField 1x UILabel

if (editing is commenced && value changed) {
    if (.length == 2) {
        Move onto next UITextField;
    }
} 

And display the UILabel Masked over the textfields, but also customise the textfields so 3 appears to be one.

-- EDIT

//Programming the Textfield Mask
-(void)reformatAsCardNumber:(UITextField *)textField
{
    NSUInteger targetCursorPosition =
    [textField offsetFromPosition:textField.beginningOfDocument
                       toPosition:textField.selectedTextRange.start];

    NSString *cardNumberWithoutSpaces =
    [self removeNonDigits:textField.text
andPreserveCursorPosition:&targetCursorPosition];

    if ([cardNumberWithoutSpaces length] > 6) {
        [textField setText:previousTextFieldContent];
        textField.selectedTextRange = previousSelection;
        return;
    }

    NSString *cardNumberWithSpaces =
    [self insertSpacesEveryFourDigitsIntoString:cardNumberWithoutSpaces
                      andPreserveCursorPosition:&targetCursorPosition];

    textField.text = cardNumberWithSpaces;
    UITextPosition *targetPosition =
    [textField positionFromPosition:[textField beginningOfDocument]
                             offset:targetCursorPosition];

    [textField setSelectedTextRange:
     [textField textRangeFromPosition:targetPosition
                           toPosition:targetPosition]
     ];
}

-(BOOL)textField:(UITextField *)textField
shouldChangeCharactersInRange:(NSRange)range
replacementString:(NSString *)string
{
    previousTextFieldContent = textField.text;
    previousSelection = textField.selectedTextRange;

    return YES;
}

- (NSString *)removeNonDigits:(NSString *)string
    andPreserveCursorPosition:(NSUInteger *)cursorPosition
{
    NSUInteger originalCursorPosition = *cursorPosition;
    NSMutableString *digitsOnlyString = [NSMutableString new];
    for (NSUInteger i=0; i<[string length]; i++) {
        unichar characterToAdd = [string characterAtIndex:i];
        if (isdigit(characterToAdd)) {
            NSString *stringToAdd =
            [NSString stringWithCharacters:&characterToAdd
                                    length:1];

            [digitsOnlyString appendString:stringToAdd];
        }
        else {
            if (i < originalCursorPosition) {
                (*cursorPosition)--;
            }
        }
    }

    return digitsOnlyString;
}
- (NSString *)insertSpacesEveryFourDigitsIntoString:(NSString *)string
                          andPreserveCursorPosition:(NSUInteger *)cursorPosition
{
    NSMutableString *stringWithAddedSpaces = [NSMutableString new];
    NSUInteger cursorPositionInSpacelessString = *cursorPosition;
    for (NSUInteger i=0; i<[string length]; i++) {
        if ((i>0) && ((i % 2) == 0)) {
            [stringWithAddedSpaces appendString:@":"];
            if (i < cursorPositionInSpacelessString) {
                (*cursorPosition)++;
            }
        }
        unichar characterToAdd = [string characterAtIndex:i];
        NSString *stringToAdd =
        [NSString stringWithCharacters:&characterToAdd length:1];

        [stringWithAddedSpaces appendString:stringToAdd];
    }

    return stringWithAddedSpaces;
}

Then to call it

[_answerTextField addTarget:self
                  action:@selector(reformatAsCardNumber:)
        forControlEvents:UIControlEventEditingChanged];

I need the pre-determined text such as __:__:__ or preferably __h:__m:__s so when you start typing you get 00h:0_m:__ as you fill out.

As right now, I get `` then when I start typing I get 00:0 etc..

Answer 1

Use the textFieldShouldChange method to modify the input / move the cursor as you see fit BEFORE it is updated on the screen

it is in UITextFieldDelegate:

textField:shouldChangeCharactersInRange:replacementString:
Asks the delegate if the specified text should be changed.
The text field calls this method whenever the user types a new character in the text field or deletes an existing character.

---

in addition there is also textDidChange in the delegate which works AFTER the text is shown

---

these are DELEGATE methods so you have to become the textField's delegate:

//1 conform to the delegate
@interface MyViewController <UITextFieldDelegate>

then

//2 set yourself as delegate (can also be done through IB)
textView.delegate = self;