a user action has been completed successfully
an event for which the user has previously requested notification has
To emphasize these states to the user, the AlertType can be set to
convey the context or importance of the message. For each use case
described above, there's a relevant type, such as ALARM, CONFIRMA-
TION, ERROR and INFO. These are differentiated by titles at the top of
the alert screen, icons drawn on the alert, and the sound played when it
A List object is a screen object that contains a list of choices for the user
and is, therefore, ideal for implementing choice-based menus, which are
the core user interface of most mobile devices.
A TextBox is a Screen object that allows the user to enter and edit text
in a separate space away from the form. It is a Displayable object and
can be displayed on the screen in its own right. Its maximum size can be
set at creation, but the number of characters displayed at any one time is
unrelated to this size and is determined by the device itself.
A Form object is designed to contain a small number of closely-related
user interface elements. Those elements are, in general, subclasses of the
Item class and we shall investigate them in more detail below. The Form
object manages the traversal, scrolling and layout of the items.
Items enclosed within a form may be edited using the append() ,
delete() , insert() and set() methods. They are referred to by
their indexes, starting at zero and ending with size()-1 . Items are
organized via a layout policy that is based around rows. The rows
typically relate to the width of the screen and are constant throughout.
Forms grow vertically and a scroll bar is introduced as required. If a form
becomes too large, it may be better for the developer to create another
screen. Users can interact with a Form and a CommandListener can
be attached to capture this input using the setCommandListener()
method. An individual Item can be given an ItemCommandListener ,
if a more contextual approach is required by the UI.