Summary

The main focus of this chapter has been how to set and retrieve the values stored in an object’s instance variables using the new Objective-C 2.0 declared property feature. These are the main points to remember about accessing instance variables and using properties:

• You should access an object’s instance variables by using accessor methods to get and the instance variable’s value. You shouldn’t access the instance variables directly from outside the object.

• The @property statement lets you declare the accessor methods in a convenient shorthand form.

• Property declarations provide extra information about the accessor methods such as whether object instance variables are assigned, retained, or copied, and whether the accessors use locks to ensure atomicity.

• When accessors are declared with a property declaration, you can ask the compiler to create the code for the accessor methods for you by using a @synthesize directive. The synthesized accessor reflects the attributes specified in the @property statement.

• Using @synthesize creates very basic accessors that only set or retrieve the property value. If you need to do extra processing when accessing a property (for example, clamping an input value to a specified range), you can omit the @synthesize statement (or use @dynamic) and code the accessor for the property yourself.

• Objective-C 2.0 also introduces the dot syntax, a shorthand way to call accessor methods.