What You’ll Learn in This Hour: |
What makes an iPhone an iPhone Where to get the tools you need to develop for the iPhone How to join the iOS Developer Program The need for (and use of) provisioning profiles What to expect during the first few hours of this book
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The iPhone opens up a whole
realm of possibilities for developers—a multitouch interface, always-on
Internet access, video, and a whole range of built-in sensors can be
used to create everything from games to serious productivity
applications. Believe it or not, as a new developer, you have an
advantage. You will be starting fresh, free from any preconceived
notions of what is possible in a handheld application. Your next big
idea may well become the next big thing on Apple’s App Store.
This hour will get you
prepared for iPhone development. You’re about to embark on the road to
becoming an iPhone developer, but ’you need to do a bit of prep work
before you start coding.
Welcome to the iOS Platform
If you’re reading
this book, you probably already have an iPhone, and that means you
already understand how to interact with its interface. Crisp graphics,
amazing responsiveness, multitouch, and hundreds of thousands of
apps—this just begins to scratch the surface. As a developer, however,
you’ll need to get accustomed to dealing with a platform that, to
borrow a phrase from Apple, forces you to “think different.”
Display and Graphics
The iPhone screen is 320×480
points—giving you a limited amount of space to present your
application’s content and interface (see Figure 1). Notice that I said “points”, and not pixels! Prior to the release of the iPhone 4’s Retina display, the iPhone was
320×480 pixels. Now, the actual resolution of an iOS device is
abstracted behind a scaling factor. This means that while you will be
working the numbers 320×480 for positioning elements, you may have more
pixels than that. The iPhone 4, for example, has a scaling factor of 2,
which means that it is really a (320×2)×(480×2) or 640×960 resolution
device. Although that might seem like quite a bit of screen real
estate, remember that all these pixels are displayed in a screen that
is roughly 3.5-inch″ diagonal.
320 points
480 points
Did You Know?
We’ll look more at how
scaling factors work when we position objects on the screen throughout
the book. The important thing to know is that when you’re building your
applications, the iOS will automatically take the scaling factor into
play to display your apps and their interfaces at the highest possible
resolution with rarely any additional work on your part!
Although this might seem
limiting, consider that desktop computers only recently exceeded this
size and many websites are still designed for 800×600. In addition, the
iPhone’s display is dedicated to the currently running application. You
will have one window to work in. You can change the content within that
window, but the desktop and multiwindow application metaphors are gone.
The screen limits
aren’t a bad thing. As you’ll learn, the iPhone development tools give
you plenty of opportunities to create applications with just as much
depth as your desktop software—albeit with a more structured and
efficient interface design.
The graphics that you
display on your screen can include complex animated 2D and 3D displays
thanks to the OpenGL ES implementation available on all iPhone models.
OpenGL is an industry standard for defining and manipulating graphic
images that is widely used when creating games. The iPhone 3GS and 4
improve these capabilities with an updated 3D chipset and more advanced
version of OpenGL (ES 2.0), but all the models have very respectable
imaging abilities.
Application Resource Constraints
As with the HD displays on
our desktops and laptops, we’ve grown accustomed to processors that can
work faster than we can click. The iPhone uses a ~400MHz ARM in the
early models, a ~600MHz version in the 3GS, and a 1GHz A4 in the iPhone
4. The A4 is a “system on a chip” that provides CPU, GPU, and other
capabilities to the device and is the first Apple-designed CPU to be
used in quite a while.
Apple has gone to great
lengths to keep the iPhone responsive regardless of what you’re doing.
Unfortunately, that means that unlike the Mac OS, your iPhone’s
capability to multitask is limited. In iOS 4, Apple has created a
limited set of multitasking APIs for very specific situations. These
enable you to perform some tasks in the background, but your
application can never assume that it will remain running. The iOS
preserves the user experience beyond above all else.
Another constraint that you’
need to be mindful of is the available memory. In the original and
iPhone 3G devices, 128MB of RAM is available for the entire system, including your application.
There is no virtual memory, so you must carefully manage the objects
that your application creates. In the iPhone 3GS Apple upped the ante
to 256MB and, with the iPhone 4, Apple has graciously provided 512MB!
This is great for us, but keep in mind that there are no RAM upgrades
for earlier models!
By the Way
Throughout the book,
you’ll see reminders to “release” memory when you’re done using it.
Even though you might get tired of seeing it, this is a very important
process to get used to.
Connectivity
The iPhone has the ability
to always be connected to the Internet via a cellular provider (such as
AT&T in the United States). This wide-area access is supplemented
with built-in WiFi and Bluetooth in all iPhone models. WiFi can provide
desktop-like browsing speeds within the range of a wireless hot spot.
Bluetooth, on the other hand, can be used to connect a variety of
peripheral devices to your iPhone, including a keyboard!
As a developer, you can make
use of the Internet connectivity to update the content in your
application, display web pages, and create multiplayer games. The only
drawback is that applications that rely heavily on 3G data usage stand
a greater chance of being rejected from the App Store. These
restrictions have been lessened in recent months, but it is still a
point of frustration for developers.
Input and Feedback
The iPhone shines when it
comes to input and feedback mechanisms and your ability to work with
them. You can read the input values from the capacitive multitouch
(five-finger!) screen, sense motion and tilt via the accelerometer and
gyroscope (iPhone 4), determine where you are using the GPS (3G/3GS),
see which way you’re facing with the digital compass (3GS and iPhone
4), and understand how the phone is being used with the proximity and
light sensors. The phone itself can provide so much data to your
application about how and where it is being used that the device itself
truly becomes a controller of sorts—much like (but surpassing!) the
Nintendo Wii.
The iPhone also supports
capturing pictures and video (3GS and iPhone 4) directly into your
applications, opening a realm of possibilities for interacting with the
real world. Already applications are available that identify objects
you’ve taken pictures of and that find references to them online (such
as the Amazon Mobile app).
Finally, for each action
your user takes when interacting with your application, you can provide
feedback. This, obviously, can be visible feedback on the screen, or it
can be high-quality audio and force feedback via vibration. As a
developer, you can leverage all these capabilities (as ‘you’ll see
learn this book).
That wraps up our quick
tour of the iOS platform. Never before has a single device defined and
provided so many capabilities for a developer. As long as you think
through the resource limitations and plan accordingly, a wealth of
development opportunities awaits you.
Did You Know?
Although this book targets the
iPhone specifically, nearly all the information carries over to
development for the iPod Touch and iPad. These systems differ in
capabilities, such as support for a camera and GPS, but the development
techniques are otherwise identical.
