Although it seems very Cliché, our first iPhone app will be a Hello World program. Mostly everyone starts out programming with a Hello World exercise, so let’s not stray from the group since it seems they are doing well…
As we go through this series I will explain concepts like Objective-C (the programming language iOS apps are written in), iPhone development, and programming in general…
Lets get started!
1. Open Xcode and click “Create a new Xcode Project”
2. Select “View-Based Application” and click choose…
3.Give your app the name “HelloWorld”
When the application project opens you will be presented with a view similar to this…
If you click on the files from the classes folder you will be able to see the code in the right window. As you can see Apple gives you some pre-written code that is commented out. On that note, I’ll explain to you what a comment is… A comment is text that will not be executed by the compiler (Xcode). A comment that is just one line will with start with a “//” and a comment that is more than one line long is started with a “/*” and ended with a “*/”… Comments come in very useful when developing programs. You can use comments to document code for later viewing or to document code for other developers.
Before we start writing our first app I need introduce and explain a few concepts, OOP (Object Oriented Programming), MVC (Modal View Controller), and “.h” and “.m” files. Let me take a shot at explaining OOP to you… The Object in Object Oriented Programming is basically two files of code (.h and .m) that work together so that a developer can call that code in their own programs. This provides a massive framework for developers so that they don’t have to start completely from scratch. If you are having troubles understanding the object oriented programming concept you can ask me questions by emailing me at Derek@homeschooldev.com.
Now lets start with the “.h” and “.m” files. Open up the “HelloWorldViewController.h” file by single clicking on the file. As you can see, the code is displayed in the window to the right. A “.h” (header) file is a basically a blue print to an object and a “.m” (implementation file) is where all the code is implemented and executed from. If you don’t understand this concept yet, that’s ok, we will come back to it…
MVC (Model View Controller) is something that is used when developing apps for iOS and Mac OS X. It is something that splits up the code and the actual interface that the user sees. Model, is the users data and the data you display to the user, View is what the user interfaces with and a controller is your code that manages the link between the view and the model. This concept may seem edgy now, but it will grow on you very quickly and makes the life of a programmer much easier and organized.
Lets get coding!
In the header file, “HelloWorldViewController.h”, we are going to declare an IBOutlet. An IBOutlet is what connects your code to a visual object, such as a label or a button.
3. Between the curly braces type “IBOutlet UILabel *label;” and outside the curly braces type “-(IBAction)button;”
An IBAction is a method (block of code) that can be called. An IBAction is recognized by the view and allows you to connect that specific method (block of code) to a UI item, such as a button so that the button will execute that block of code.
That’s all we need to do in the header file… Now lets start designing the interface.
4. Open the folder named “Resources” and double click the file named “HelloWorldViewController.xib”
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