Item
Class Item is a superclass of all those components
that can be attached to a Form. An Item can be contained only
in a single Form at a time. The application must remove the item from
the Form in which it is currently contained before inserting it into
another Form.
All Item objects can have a label field, which is a String representing the
title of the Item. If the label String is null, then
no label is presented. The label is typically displayed near the Item
when the Item is visible on the screen. If the screen is scrolling, the
implementation tries to keep the label visible at the same time as the
Item.
10.1.1 ItemStateListener
When the user changes an editable Item in a
Form, the application can be notified of the change by implementing the
ItemStateListener interface and setting the listener on the
Form. The itemStateChanged method of the
ItemStateListener set on the Form is called automatically when
the value of an interactive Gauge, ChoiceGroup,
DateField, or TextField changes. The listener is set for the
Form using the setItemListener method. It is not expected that
the listener is called after every event that causes a change. However, if the
value has changed, the listener is called sometime before it is called for
another Item, or before a Command is delivered to the
ItemStateListener of the Form.
Continuing the example started in Section 9.4, "Form," the
ItemStateListener would be set as follows:
form.setItemListener(this);
10.1.2 Item Commands
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In MIDP 2.0, context-sensitive Commands can be added
to Items. Commands added to an Item are made
available to the user only when the focus is on that
Item. As with Commands added to Displayables, the
device implementation decides how the Commands are presented in the
user interface. For example, the Commands might appear as a context-sensitive menu for the Item or as a normal
menu when the Item is being manipulated by the
user. |
Context-sensitive Commands are used much like ordinary
Commands in Displayables. The addCommand and
removeCommand methods of the Item class control which
Commands are associated with Items. There is a dedicated
listener type called ItemCommandListener that is
notified automatically when the user activates a Command of an
Item. The listener of an Item is set with the
setItemCommandListener method.
One of the Commands of an Item can also be
chosen as the default Command using the method
setDefaultCommand. A device may make this Command more easily
accessible, for example, using the "Select" key
of a device if such a key is available.
For an example on item command use, refer to the sample code in
Section
10.2.1, "Appearance Modes."
Sections
