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Chapter 3 Examining Device Property Files 33
There are two ways you can do a button press at the same time as pressing Shift or
Alt:
■
Map the buttons to the keyboard, as in the previous section, and press the key
associated with the button at the same time as the Shift or Alt keys
■
Press the button Shift-Lock or Alt-Lock and then do the button press. Press
Shift-Lock or Alt-Lock again to revert to the initial state.
For example:
keyboard.handler.qwerty.A = 'a' 'A' '?'
Assigning Abstract Commands to Buttons
Abstract commands are provided in the MIDP specification in order to allow an
application to issue a screen command without having to take into account how the
user selects that command on a specific device—making the application more
portable. The idea is to separate the semantics of the command from its execution
on the device. The semantics are defined in the application and the execution is
defined in the implementation of MIDP on the specific device.
The semantics of an abstract command include:
■
Label—the command name for display purposes
■
Type—the category of the command, for example BACK or HELP. The command
type is used to help determine how a command is mapped onto a device
■
Priority—a priority number. The command priority is used to help determine
how a command is mapped onto a device.
In the MIDP Reference Implementation, which underlies the J2ME Wireless Toolkit,
there is an implicit order of precedence among the command types. This command
precedence also impacts on the assignment of a command to a preferred button. If
two commands of different types are vying for the same button, the command
whose type has higher precedence prevails.
TABLE 3 shows the abstract command types in order of precedence in the J2ME
Wireless Toolkit and the MIDP Reference Implementation:
TABLE 3
Abstract Command Types in Order of Precedence
Command Type Description
BACK Returns the user to the logically previous screen
EXIT Exits from the application
CANCEL Standard negative answer to a dialog implemented by the
current screen
STOP Stop some currently running process or operation