iOS 6 Programming Cookbook

1.13. Defining Functionality for Classes

Problem

You want to define some functionality for your classes and allow them to be reused later.

Solution

Create instance or class methods for your classes in order to create reusable blocks of code, or simply call a method in your program.

Discussion

Nearly every programming language creates procedures and functions to encapsulate specific functionality, especially functionality that the programmer uses over and over. Some languages consider “procedure” and “function” just terms for the same thing, while others make a distinction between them. A procedure is a block of code with a name and an optional set of parameters. It does not have a return value. In Objective-C, a procedure returns void to indicate it does not return a value. A function is similar but does have a return value. Here is a simple procedure (with an empty body) written in C:

void sendEmailTo(const char *paramTo,
                 const char *paramSubject,
                 const char *paramEmailMessage){

  /* send the email here ... */
}

This procedure is named sendEmailTo and has three parameters: paramTo, paramSubject, and paramEmailMessage. We can then call this procedure as follows:

sendEmailTo("[e-mail]",
            "My Subject",
            "Please read my email");

Turning this procedure into a function that returns a Boolean value, we will have code similar to this:

BOOL sendEmailTo(const char *paramTo,
                 const char *paramSubject,
                 const char *paramEmailMessage){

  /* send the email here ... */

  if (paramTo == nil ||
      paramSubject ...