Eric Giguere demonstrates how to store persistent user preferences in a MIDlet (mobile applications based on the Mobile Information Device Profile -- MIDP) as a single record rather than as several individual records. These preferences can be anything from an email address to information relating to recent uses of the application, such as which screen was last displayed. The Tech Tip includes examples of code.

Giguere recommends using the Singleton design pattern to ensure that preferences are read and written consistently throughout the application. The Prefs class must be coded so that the MIDlet can have only one instance of it. The MIDlet will call either its single-instance getInstance method or MIDlet.getAppProperty to get the application descriptor properties, which is a convenient source of default values for user prefererences.

With the Singleton obtained, the MIDlet can use one of three get methods to obtain a property value: getStringProperty(), getBooleanProperty() or getIntProperty(). Each method takes two parameters: the property name and the default value to return if the property is undefined.

To change the value of a property, the MIDlet calls setStringProperty(), setBooleanProperty() or setIntProperty(). The property is stored internally in the Prefs object, but not immediately written to the record store. Because writing to the record store can be a slow operation on some devices, Prefs does so only when its save() method is called.

With a simple MIDlet, Giguere shows how to use the Prefs class. The MIDlet allows users to test it, set appropriate values, exit, restart the application and verify that the desired preferences were saved.

Additional information on record stores is available in the JavaTM 2 Platform, Micro Edition (J2METM) Technical Tips, which include Record Management System Basics and Using Record Stores Efficiently.

http://wireless.java.sun.com/midp/ttips/preferences [...read more...]

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