Resize UITextField Based On Text Entered - objective-c

Question

I have UITextfield that is set to show only 1 character upon initialization, however I use constraints to make the field be able to expand as needed.
My constraint:
#"H:[txtField(<=80)]-14-|
When I set the textField via the text attribute it resizes perfectly, however when I try and enter it in via the keyboard the best I can get is to use sizeToFit inside the shouldChangeCharactersInRange...which kind of works but instead of the dollar amount moving inward to the left on the iphone it moves outward to the right and off the screen.
How would I make it move inward to the left?

Answer 1

I ended up using this little bit I found on StackOverflow in the
shouldChangeCharactersInRange
double currentValue;
NSString *str;
if(![textField.text length]){
str = #"$ 0.00";
}else{
str = textField.text;
}
currentValue = [[str substringFromIndex:1] doubleValue];
double cents = round(currentValue * 100.0f);
if ([string length]) {
for (size_t i = 0; i < [string length]; i++) {
unichar c = [string characterAtIndex:i];
if (isnumber(c)) {
cents *= 10;
cents += c - '0';
}
}
} else {
// back Space
cents = floor(cents / 10);
}
textField.text = [NSString stringWithFormat:#"%.2f", cents / 100.0f];
//Add this line
[textField setText:[NSString stringWithFormat:#"$%#",[textField text]]];
return NO;