Datasheet

26
Part I: Getting Started
has to select or manipulate with a finger be a minimum of 44 x 44 pixels in
size), and spaced far enough apart so that users’ fingers can find their way
around the interface comfortably.
You also can do only so much by using fingers. There are definitely a lot
fewer possibilities when using fingers than the combination of multi-button
mouse and keyboard.
Because it’s so much easier to make a mistake when using just fingers, you
also need to ensure that you implement a robust — yet unobtrusive — undo
mechanism. You don’t want to have your users confirm every action (it
makes using the application tedious), but on the other hand, you don’t want
your application to let anybody mistakenly delete a page without asking, “Are
you sure this is what you really want to do?” Lost work is worse than tedious.
Another issue around fingers is that the keyboard is not that finger-friendly.
I admit it, using the iPhone keyboard is not up there on the list of things I
really like about my iPhone. So instead of requiring the user to type some
information, Apple suggests that you have a user select an item from a list.
But on the other hand, the items in the list must be large enough to be easily
selectable, which gets back to the first problem.
But again, like the small screen, this limitation can inspire (okay, may force)
you to create a better application. To create a complete list of choices, for
example, the application developer is forced to completely understand the
context of (and be creative about) what the user is trying to accomplish.
Having that depth of understanding then makes it possible to focus the appli-
cation on the essential, eliminating what is unnecessary or distracting. It also
serves to focus the user on the task at hand.
Limited computer power, memory, and battery life
As an application designer for the iPhone, you have several balancing acts to
keep in mind:
✓ Although significant by the original Macintosh’s standards, the com-
puter power and amount of memory on the iPhone are limited.
✓ Although access to the Internet can mitigate the power and memory
limitations by storing data and (sometimes) offloading processing to a
server, those operations eat up the battery faster.
✓ Although the power-management system in the iPhone OS conserves
power by shutting down any hardware features that aren’t currently
being used, a developer must manage the trade-off between all those
busy features and shorter battery life. Any application that takes advan-
tage of Internet access by using Wi-Fi or the 3G network, core location,
and a couple of accelerometers is going to eat up the batteries.
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