Configuring and Applying a Formatter

When you create a date or number formatter object, you can configure it in many ways, but the primary attributes are formatter style and locale. You can give NSNumberFormatter objects a decimal, currency, percent, scientific, or “spell-out” style (for example, “25” to “twenty-five”). You can give NSDateFormatter objects both date and time styles in a range of explicitness, for example, from “11/22/2009” to “Sunday, November 22, 2009 AD”.

You may also apply an NSLocale object to a formatter object so that it reflects a certain locale; for example, “1.02” in U.S. English would be “1,02” in French. To get the current locale (set by the user), call the NSLocale class method currentLocale.

After you have configured a date or number formatter, you apply it to a string obtained from the user interface (typically a text field) to obtain the value object; or you apply it to an NSDate or NSNumber object and write the resulting string to an object in the user interface. The methods you call for these purposes are dateFromString:, stringFromDate:, numberFromString:, and stringFromNumber:.

In OS X, You Can Attach a Formatter to a Cell

On OS X, you can associate a number or date formatter object with a cell object, either programmatically or in Interface Builder. The conversion between string and number or date object occurs automatically—you do not have to call any method to perform the conversions. The cell object can be associated with objects other than text fields. For example, you can assign formatter objects to the cells in a table view or outline view.