Palm webOS: Developing Applications in Javascript Using the Palm Mojo Framework – Page 2
Palm webOS is designed for mobile, battery-operated devices with limited though variable screen sizes, and a touch-driven user interface. User interaction is centered on one application at a time, though applications, once launched, continue to run until closed even when moved out of the foreground view. There is a rich notification system enabling applications to subtly inform or directly engage the user, at the application’s discretion.
Navigation is based upon a few simple gestures with optional extensions that create a rich vocabulary of commands to drive powerful navigation and editing features. To start with though, all you need to know is:
- tap (act on the indicated object). Commonly in a view that contains clusters or lists of items, tapping reveals information contained in an item. This can be thought of as an open function, which changes the nature or context of the view to be about the selected item exclusively. Alternately, a tap will change an object’s state such as setting a checkbox or selecting an object.
- back (the inverse of open). This feature looks like the opposite of a tap: the item compresses down to its summary in the containing context where it belongs. Typically, it reverses a view transition, as going from a child view to a parent view.
- scroll (flick and quick drags are used to scroll through lists and other views.
Beyond this, you can learn to pan, zoom, drag & drop, switch applications, switch views, search, filter lists and launch applications. But to begin with, only these three gestures are needed to use a webOS device.
When you turn on a webOS device, the screen displays the selected wallpaper image with the status bar across the top of the screen and, hovering near the bottom, the Quick Launch bar. The Quick Launch bar is used to start up favorite applications or to bring up the Launcher for access to all applications on the device. From this view, a search can be initiated simply by typing the search string; searches can be performed on contacts, installed applications, or to start a web search. Figure 1-2 shows both the Quick Launch bar and the Launcher.
The launched application takes over the available screen becoming the foreground application; the application’s view replaces the wallpaper image and the Quick Launch bar is dismissed. The status bar remains and is always visible except for full screen mode, which is available to applications such as the video player, or others that request it. This sequence is fluid and smooth, as you will see with all webOS transitions.
Figure 1-3 shows an application’s main view, in this case the email application’s folder view. The application view includes UI elements that make up the basic email application, in this case the inbox view displays specific folders, which when selected will open a new card with a detail view of the messages contained within the selected folder. At the bottom, the floating icons that you see are menu items. A tap to the menu icons will typically reveal another view associated with the menu action, a sub-menu or a dialog.
