Diving into the iPhone AppStore - Part 1

The iPhone madness is resonating throughout the world and the shock wave has reached Sri Lanka as well. The madness is two-fold; iPhone User madness and iPhone Developer madness! I've been fortunate enough to be a part of the staggering iPhone user base for one and half years now. Thanks to my new employer I've been able get my hands on "the other side" as well, that is, the iPhone development arena!

I'm writing this since several people have asked me about iPhone development procedures, about the AppStore and such. This should help any would-be-iPhone-developer to know about prerequisites, special considerations and possible frustrations! that he or she is going to face.

Here are the steps that you should follow to get into iPhone development using iPhoneSDK.

1. Get a Mac!

Can't I use Windows (or Linux)? Of course not! All official iPhone development tools are developed by Apple and they are Mac-only!

Well, this is costly! but you have several choices here. If you have the money, you could go for an iMac. That's apple's desktop class computer and it's sooooo pretty! Next choice would be a MacBook Pro or a lower end white MacBook. If you have a spare monitor and keyboard/mouse, you can go for a MacMini (it's kind of cheap) and plug your own monitor and keyboard to it.

If you really need it, for the initial stage of experimenting, you can try out hacked versions of MaxOS X on your PC. But these have lot of glitches in them and it's hard to get them working. More info at http://www.osx86project.org/.

MacOS X version requirement

iPhoneSDK have a minimum requirement of a certain version of MacOS X to be installed. The latest SDK version (3.1.2) requires MacOS X 10.5.8 to work. The requirement tend to elevate with most updates to the iPhoneSDK. So make sure you have necessary software updates installed on the OS.

2. iPhoneSDK

iPhoneSDK has more or less the same development tools, libraries and programming paradigms that MacOS X uses. The reason for this is that, iPhoneOS is just MacOS X with a different UI running on different hardware. In fact, apple has built iPhoneOS with the same source files of MacOS X Leopard kernel and most of the system services and libraries. So it has the same power and the architecture of the desktop class MacOS X. If you are a Mac developer (which I'm not), you'll find iPhoneSDK surprisingly similar to the development tools you've been using up to now. The only major deviation that the iPhoneOS has from MacOS X, is the UI, which is a complete rethought from top to bottom.

XCode

XCode is the IDE you'll be using. Although you are not required to use XCode, it has really nice and elegant features making it the standard choice of Mac and iPhone developers (much like Microsoft Visual Studio). XCode and other supporting development tools are freely available on the iPhone developer connection website.

Objective-C

In iPhoneSDK, You'll have to write code primarily in Objective-C. It is essentially a super set of C, meaning you can code in pure C if you want. You can think of Objective-C as an extension library to C. All it does is providing an object-oriented like syntax to access underlying C entities. The syntax may appear weird at first since it's significantly different from the "dot" notation we are used to in C-style languages. But within 10 minutes or so, you can get the hang of it.

Since we are talking about native application development here, there are no fancy runtimes available for you. Actually, Objective-C itself has a runtime to do stuff like wrapping/unwrapping Objective-C classes from and to their equivalent C data structures. But it's not as powerful as .Net CLR or Java virtual machine. In my opinion, iPhoneSDK development stands between Win32 native development and .Net development. You don't have to go into so deep as native Windows programming, but you don't also have a large runtime feature set like .Net. For example, Objective-C runtime, doesn't have a garbage collector so you have to release resources manually when you finish using them. Somewhat similar to free() in C but not exactly the same. You'll understand these fine differenciations when you read the subject matter.

For more info on everything regarding iPhone SDK and AppStore, register on iPhone Developer Connection.

3. Testing the apps

iPhoneSDK comes with a nice iPhone simulator that you can use to test your applications. Obviously this doesn't have all the features of a real iPhone but you can emulate most of the functionality here. One thing to keep in mind is that DO NOT test application performance in the emulator. Since the emulator runs using your desktop CPU and hardware, applications run significantly faster on it. But it should be enough for most day-to-day business class applications.

If you do need to test your application on a real device however, you might want to consider buying an iPhone or an iPodTouch (iPodTouch lacks some hardware features the iPhone has). In addition to that, you need to register on the iPhone Developer Program ($99/year) in order to acquire a developer certificate. You need that certificate to test your applications on a real iPhone.

Continue to Diving into the iPhone AppStore - Part 2

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iPhone: from a developer's point of view

First of all, I must say that, although the name suggests, the iPhone is not a phone. In short terms it’s an apple computer that fits on your palm which has GSM calling/SMS capabilities. (Maybe that’s why it lacks some of the features that Nokia high end phones provide!). It runs a light-weight version of Mac OS X and it has the same architecture of a Von Neumann computer up to a certain extent. So as a developer, one should keep in mind that developing native applications for the iPhone is much like developing GUI applications for Mac OS (or Microsoft Windows). When compared to other smart phones on the market, iPhone is inherently much much more powerful and flexible than them. Not only because it’s a computer, but because it’s a computer with a big multi-touch screen, a 3 axis accelerometer sensor and a Geo-Locator system which can report the Geographical location of the iPhone using signals from cell towers or Wi-Fi hotspots.

Although the iPhone is like a computer, it has significant differences compared to a desktop machine. It’s usage is entirely different. So developer’s should keep that in mind when developing applications.

• The screen is compact compared to a desktop monitor, although it’s bigger compared to other phones. So only most relevant features for a mobile device must be included in the application.

• Users use their fingers instead of the mouse and the keyboard to give inputs to the iPhone. So GUI elements must be big enough to be touched by the user.

• iPhone users use the device when they are on the move. So they need to access important information as quickly as possible without going through so many screens or inputs.

Application Development

I’m a windows programmer. I had never used an apple machine nor did I knew about MacOS system architecture. But after going through iPhone SDK articles I found out that MacOS and iPhone GUI architecture closely resembles Win32 GUI programming. So I found it very easy to follow up on iPhone SDK with the knowledge of Windows GUI event driven architecture. The GUI framework in iPhone is known as UIKit which is a component of Cocoa Touch as opposed to Cocoa in MacOS.

iPhone SDK uses a language called Objective-C to write programs. At first the syntax was a little bulky for me. But you can catch up on the syntax in 10 minutes. It’s the same object oriented architecture in a different syntax.

iPhone SDK has a nice GUI class hierarchy which reminds me of Microsoft .Net Framework Windows Forms class hierarchy. These classes use delegation to receive and handle events in a way similar to Win32 callbacks and .Net framework delegates. For example, the developer can register an event handler for the “touch” event of a button.

(Portion of UIKit classes. Image extracted from an ADC article)

iPhone SDK encourages developers to use MVC (Model, View, Controller) architecture in their application. This ensures that the GUI is separated from the application logic and the data model.

(MVC architecture)

Multi-Touch Events

Just like MacOS and Windows, Cocoa touch framework uses an event-driven architecture to raise and handle events. Unlike traditional keyboard and mouse events on a desktop, the iPhone has “touch” events. When user’s fingers touches the iPhone screen, the touch sensor sends information of each finger touch to the OS. This is how multi-touch technology works. When multiple fingers touch the screen, the event handlers for any GUI elements receive information about all the touches through multiple event objects.

The iPhone SDK API directly supports simple tough gestures such as swipes, double taps and pinches. To handle more complex gestures you can examine the event objects to generate your own custom events.

3 Axes Accelerometer

The iPhone has an accelerometer which can report acceleration data of the device in X,Y and Z axes (see image). Because of the gravity of the earth, the 3 accelerometers record different accelerations in 3 axes.

(Image extracted from an ADC article)

Why do a phone need an accelerometer? Well, using the iPhone, you can do amazing things with the help of the accelerometer. Using it, you can get the orientation of the device in 3D space at any given time. You can create orientation aware applications that responds to the physical orientation of the device. The application can change dynamically depending on how the user holds it. A basic use of this is demonstrated by the built-in Photo application where photos automatically switches to the landscape mode when user holds the iPhone horizontally.

More advanced and exciting use of it is gaming. (iPhone uses OpenGL ES to render 3D graphics). You can combine the accelerometer data into your game to use the whole phone as a joystick. When the user tilts the phone just like a joystick, the objects on the game can respond accordingly to create an exciting user experience. This video of iPhone SDK event shows OpenGL ES and accelerometer in action. It shows an application in which the user can “shake” the phone to perform undo operations and a 3D game where the gamer can fly the fighter jet by tilting the iPhone like a joystick.

Applications can register an event handler to receive acceleration events. A reporting frequency can be specified. The default is 100 times per second. This is good for games. But you should use a frequency to match your application’s needs in order to save the battery life.

Resource Management

Since iPhone is a mobile device which runs on battery, every effort must be made to make your applications efficient. Developer should take care of releasing resources which are not needed. Mac OS X natively has a garbage collector to free up resources (wow, isn’t it! Windows doesn’t have it!). But iPhone doesn’t have the luxury of a garbage collector since it’s restricted to a low power consumption environment. The SDK uses reference counting mechanism to keep track of the resources which are in use.

One Application At a Time

iPhone can run only one application at a time. Of course, the OS kernel and few low-level demon threads keep on running all the time, but only one user application can be run at a time. This ensures low processor usage and the applications get to have the full resources of the device at their expense. So if a user receives a phone call or presses the Home button while they are working on an application, that application really exits. This is a one major fact that iPhone application developers should take into account.

Although there are some benefits of this exclusive application execution, developers have to make their applications to adapt to this environment. Suppose a user receives a phone call while they are editing a photo in a photo editing application. Application exits and phone call application launches. The application should be able to restore it’s last working status when the user goes back to that application after the phone call. So the developer must save the status of the application when it quits and restore it back when it is launched again. All application receive notifications when the system is going to quit the application. As I understand it, it maybe something similar to the “Kill” signal in Linux.

This is an important design aspect in the iPhone. Almost every built-in applications have this restore feature giving the illusion that the application keeps running in the background when it is interrupted. What they actually does is, save the state when they are exited, and restore themselves back when they are launched the next time.

Development Tools

iPhone SDK comes with a rich set of tools which can aid developers in developing iPhone applications. XCode is the IDE for iPhone applications. XCode only runs on Mac OS X or later. It has instruments which can remotely monitor and debug your applications. Deploying applications is easy. Only a single button click; your application is compiled and loaded into the iPhone. You can build your application into a real iPhone connected to the computer or you can use the iPhone simulator that comes with the SDK. The aforementioned video shows the remote application performance monitor, monitoring the performance of the 3D game. I must say, it’s as good as Microsoft Visual Studio 2008 (if not better). As a .Net framework developer, I find it easy to adapt to iPhone development.

Conclusion

This article only describes most exiting features of the iPhone SDK. There are many more features such as OpenGL, Media framework, Animations, Microsoft Exchange support etc… If you are interested I suggest you register on the Apple Developer Connection (free). You gain access to lots of documents, videos (through iTunes) and sample applications.

Finally, I must say, iPhone truly is an amazing device which opens the door for a new generation of mobile devices. Apple has developed a flexible framework and tools that developers would love to develop on. They launched the iPhone SDK on March 6 (watch videos). They will release iPhone 2.0 software update on June. As for me, I’m just waiting until my iPhone arrives on April. Let’s hope for the best!

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