Perhaps try implementing the delegate method:
- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view
You could treat it as a passthrough (just passing back the reusingView parameter) but each time it was called you would know that view was coming on the screen as the user scrolled - then you could calculate how many views offset from this one the center view was.
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