iOS 5 Programming Cookbook

1.12. Creating Custom Classes

Problem

You want to pack a set of related functionalities into a reusable entity, for immediate or later use.

Solution

Create your own classes.

Discussion

Let’s say you want to write a calculator program. You are creating the user interface and you want each button on the calculator to have a black background, white text and have a bump user interface, just like a real button. Aren’t these all common traits between all the buttons you want to place on your UI? You got! It’s best that we create a class to represent all our buttons and write the code once and reuse multiple times.

Classes in objective-C are normally represented with the following code:

Header file

This is where you define what your class basically does: accept user input, rotate a shape, or whatever. But the header file does not implement any of that functionality. Header files have a .h extension.

Implementation file

After defining the functionality of your class in the header file, here you write the actual code for all that functionality. Implementation files have a .m extension.

Let’s go a bit more into detail by going ahead and creating a class. Follow these steps:

1. In Xcode, go to the File menu and then select New File.

2. A dialog will appear, similar to that shown in Figure 1-23. Here simply select Objective-C class from the list to the right. Make sure iOS is selected on the lefthand side. After this, press the Next button.

3. In the next screen, make sure the Subclass of text box says NSObject