Since the announcement of the iPad there have been mixed views towards the iPhone development community, mainly to do with the fact that are potentially two different platforms to cater for. However, this can be an advantage to some developers, especially financially.
The iPad is backward compatible with iPhone application, since they will be scaled up by the iPad to make use of the larger screen (if required). That said, the iPad is a completely different device in it’s own right and is extremely different to the iPhone, mainly due to the larger screen surface.
However, when developing applications for the iPad, you must make sure you cover:
Orientation Support for rotation
The iPad does not have a ‘right’ way up, it can be used in the same direction as the iPhone (portrait) or in the landscape orientation (on its side). Therefore, it is crucial that your application is able to rotate in either direction.
All iPhone apps which use the UINavigation controller (for drilling down information, such as the settings app) can now take advantage of the new view controller. This allows simulataneous viewing of the list (in landscape orientation) and the detailed view (as a two panel selector UI pattern). The regular orientation is still available in portrait orientation. The new and improved UIKit in iPhone 4.0 will allow these functions to be controlled for your iPad application.
Due to the size of the screen on the iPhone it is not common practice to have modal dialogues (except for third party ones like Facebook connect auth). The iPad SDK allows modal dialogues, modeless dialogues and attactive menus.
All applications which use the master/detail view will automatically convert the master list into a popover menu which the iPad is placed in the landscape orientation. The same technique can be used to create menus to show pages or dialogues.
Traditional tabs normally appear at the top of an application (except on the iPhone). iPad applications now have the option to place tabs at the top or at the bottom of the application, allowing tabs to be put inside popover views.
Again, due to the increased screen size of the iPad, UITableViews may now have multiple columns.
Although technically speaking you can have as many finger gestures as you like (as long as you it’s under 10 fingers of course!), but the iPhone’s limited screen size sort of made anything more than two fingers a pain to use.
The deliciously large screen size of the iPad now allows us to use a bunch of new gestures as seen on the MacBook trackpad.
Videos need consume the entire screen for the iPad. Video can now be restricted to a small portion or area of the screen.
The iPad also supports wireless headsets and microphones, allowing hands-free voice-driven control of the apps.
Improved CoreGraphics technology allows apps to generate PDF content, allow reports to be generated on the fly by using the SDK.
Compass and Location
GPS location and compass technology is only available on 3G models of the iPad.
Text input and keyboards
Each text field input will support spell checking and auto-completion (much like iPhone 4.0). Developers can toggle this behaviour to suit the needs of the application.
Virtual keyboards can also be customised withina single app, allowing scientific input, IP address keys, etc.
The screen sizes for the iPhone and iPad are not proportional. The iPad tall side is 2.13x side of the iPhone and the short side is 2.4 the size of an iPhone or iPod touch.
Getting sizes of the current view via the SDK, rather than introducing magic numbers should use dimensions for games.