The iPhoneWebDev group has posted an interesting page that begins to lay out some basic standards for developing iPhone applications. Though these specifications will likely change rapidly after the device actually ships, there are some excellent guidelines applicable to current touchscreen interfaces that should also hold true for the iPhone, as well as some keen observations based on current, publicly available information.
For instance, the page points out that the interface for some already-developed Web-based, iPhone-targeted applications (like this shopping list organizer) use buttons that are too small to be readily touchable: "Touchscreen buttons should be minimum 1/2 inch high x 1/2 inch wide, with 1/8 inch between them. For the iPhone, that means never more than four buttons across. Always leave about 8 pixels space from screen edges for input as well."
The page notes that Safari for iPhone's address and navigation bars appear on each navigation at the top, but disappear as you scroll down or zoom, and points out some other common traits among built-in iPhone applications: selections slide in from right, documents zoom open, common dialogs fly up from screen-bottom, etc.
The page also opines that vertical scrolling is fine, but horizontal scrolling is generally a bad idea since users can get easily lost in the absence of horizontal scroll-bars.
A few other guidelines:
- Do not hardcode graphic width -- this forces horizonal scrolling
- Do not hardcode sizes; use percentages instead
Another page graphically dissects various elements of the iPhone's Safari browser and built-in applications, trying to discern some basic UI guidelines.