Objective-C

Chapter 14. Using NSValue, NSNumber, and NSData

In This Chapter

• Boxing Datatypes for Use in Collections

• Working with NSNumber, and NSValue

• Using NSData and NSMutableData

As I highlight in Chapter 13, when working with collections, collections are capable of storing only valid Objective-C objects. Collections are incapable of storing scalars, structures, or other arbitrary low-level data. This is an inconvenience, but one that the designers of the Foundation framework anticipated and solved.

In order to store scalars and structures in collections, you need to use a class wrapper for these values. In other words, a class that enables you to store the value inside of an object. The Foundation framework provides three primary classes for this purpose, NSValue, NSNumber, and NSData.

The NSValue class is the simplest of these classes, providing a low-level interface for the arbitrary storage of virtually any C datatype. For example, you can store structures within it, you can store ranges within it, and so on. Once the data is stored within the NSValue instance, you can then use the instance of NSValue in a collection object. Because NSValue is relatively low level, it does not provide some of the conveniences of higher-level abstractions. Its purpose is to be flexible but it is limited in its capabilities because it can only store simple stack-allocated data. NSNumber is a subclass of NSValue. It provides a higher level abstraction to the NSValue data encoding system specifically for the purposes ...