Programming iOS 6, 3rd Edition

Properties

A property (see Chapter 5) is syntactic sugar for calling an accessor by using dot-notation. For instance, in an example earlier in this chapter we had an object with an NSMutableArray instance variable and a setter, which we called like this:

[self setTheData: d];

We could equally have said this:

self.theData = d;

The effect would be exactly the same, because setting a property is just a shorthand for calling the setter method. Similarly, suppose we were to say this:

NSMutableArray* arr = self.theData;

That is exactly the same as calling the getter method, [self theData].

In those examples, we are presuming the existence of the getter and setter methods. The declaration of an accessor method is what permits us to use the corresponding notation: the declaration of the setter lets us use property notation in an lvalue (to assign to the property), and the declaration of the getter lets us use property notation otherwise (to fetch the property’s value).

It is also possible to declare a property explicitly, instead of declaring the getter and setter methods. Declaring a property is thus a shorthand for declaring accessors, just as using a property is shorthand for calling an accessor. But declaring a property can do much more for you and your code than that. How much more it can do has increased historically, depending on what system and what version of Xcode you’re using; here’s a list of the powers of property declaration, roughly in order of increasing power, which is also roughly ...