A formatter takes a string and makes another object, typically so that the user can type something that is more than simply a string. For example, when passed the string “3/17/1975”, the
NSDateFormatter converts it into an
NSDate object that represents the seventeenth day of March in the year 1975 (Figure 26.1).
Figure 26.1. NSDateFormatter
Also, a formatter can take an object and create a string for the user to see. For example, imagine a text field that has an
NSDateFormatter. When the text field is sent
setObjectValue: with an
NSCalendarDate object, the date formatter will create a string that represents that date. ...