iPhone SDK Programming: Developing Mobile Applications for Apple iPhone and iPod touch

Chapter 3. Anatomy of an iPhone Application

In this chapter, we discuss the basic steps needed to build a simple iPhone application. First, we demonstrate the basic structure of a simple iPhone application, and then we show the steps needed to develop the application using XCode.

HelloWorld Application

In this section, we demonstrate the basic structure of a simple iPhone application. The application simply displays the message Hello World to the user. The following are the steps needed to write such an application.

1. Create a main.m function. As in any C program, the execution of Objective-C applications start from main(). You need to create the main() function in the main.m file as follows:

   #import <UIKit/UIKit.h>
   
   int main(int argc, char *argv[]) {
     NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
     int retVal = UIApplicationMain(argc, argv, nil,
                         @"HelloWorldAppDelegate");
     [pool release];
     return retVal;
   }

   The main() function starts by creating an autorelease pool and ends by releasing it. In between, it makes a call to the UIApplicationMain() function. UIApplicationMain() is declared as follows:

   int
    UIApplicationMain(int argc, char *argv[],
       NSString *principalClassName,
       NSString *delegateClassName
   )

   This function takes four parameters. The first two parameters are the parameters passed in to the main() function. These parameters should be familiar to any C programmer. The third parameter is the name of the application class. If a nil is specified, the UIApplication class is used ...