A formatter takes a string and makes another object, typically so that the user can type something that is more than just a string. For example, the
NSDateFormatter, when passed a string like “August 17, 1967”, converts it into an
NSCalendarDate object that represents the seventeenth day of August in the year 1967 (Figure 23.1)
Figure 23.1. 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 ...