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 the string
August 17, 1967, converts it into an
NSDate object that represents the seventeenth day of August in the year 1967 (Figure 26.1).
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
NSDate object, the date formatter will create a string that represents that date. ...