MIDP Programming - Java 2 Micro Edition Application Development - page 48

static final String [] CURRENCY_FRACTIONS = {"Cent", "Cent", "Sen"} ;
In order to set the labels of the main forms TextField s for the whole and the fractional amount
according to the selected currency in the CurrencyList , you need a reference back to the main
TeleTransfer MIDlet. For this reason, you store the TeleTransfer reference in a variable
called teleTransfer . The reference is set in the constructor of your CurrencyList :
TeleTransfer teleTransfer;
In the constructor, you also add currency symbol images to the list. You need to load them, but the call
to the super constructor must be the first statement in a constructor. So you call the constructor of the
super class by specifying the title and type only. Then you create the Image s needed for each list
element, which are stored in the MIDlet suite's JAR file. You also call setCommandListener() to
register the currency list for handling commands that are issued:
public CurrencyList (TeleTransfer teletransfer) {
super ("Select Currency", Choice.IMPLICIT);
this.teleTransfer = teletransfer;
try {
append ("USD", Image.createImage ("/Dollar.png"));
append ("EUR", Image.createImage ("/Euro.png"));
append ("JPY", Image.createImage ("/Yen.png"));
}
catch (java.io.IOException x) {
throw new RuntimeException ("Images not found");
}
setCommandListener(this);
}
The final step in creating the CurrencyList is to implement the commandAction() method of
the CommandListener interface. As you already know, a List of IMPLICIT type issues a
List.SELECT_COMMAND to the registered CommandListener whenever a new element is
selected to indicate the selection change. In case of a selection change, you modify the labels of the
main form TextField s. The actual labels are obtained from the String arrays CURRENCY_NAMES
and CURRENCY_FRACTIONS . Using the teleTransfer reference, you can access the
TextField s. Finally, you call the new method teleTransfer.back() , which sets the screen
back to the main form (the back() method will be given at the end of this section):
public void commandAction (Command c, Displayable d) {
if (c == List.SELECT_COMMAND) {
teleTransfer.amountWhole.setLabel
(CURRENCY_NAMES [getSelectedIndex()]);
teleTransfer.amountFraction.setLabel
(CURRENCY_FRACTIONS [getSelectedIndex()]);
teleTransfer.back();
}
}
}
Figure 3.7 shows currency Image s and abbreviations in the CurrencyList .
Figure 3.7. The new CurrencyList .