Design

The ArrowKeys MIDlet contains one screen element, a StringItem, that indicates the orientation of the device as a printed arrow head (<, >, ^, or v). The received acceleration data from the accelerometer sensor is translated first to key events and then to these arrows. The following figure shows the main view of the MIDlet.

The MIDlet is a DataListener and, as such, it implements the DataListener.dataReceived callback to receive data from the accelerometer sensor. After setting the listener, the MIDlet receives a notification every time the accelerometer sends data.

The MIDlet converts the acceleration data to the following action events:

• Canvas.LEFT

• Canvas.RIGHT

• Canvas.UP

• Canvas.DOWN

The MIDlet converts the acceleration data by reading the acceleration values from the x and y axes. The z axis does not affect the MIDlet, and it is therefore ignored. The MIDlet compares the rotation values of the x and y axes, and selects the larger one. The MIDlet performs the actual comparison using the if(Math.abs(axis_x) > Math.abs(axis_y)) statement.

To prevent the device from changing the screen orientation, the MIDlet uses the Nokia-MIDlet-App-Orientation: portrait JAD attribute. It forces the device to remain in portrait mode regardless of how the user turns it.

For instructions on how to implement the MIDlet, see section Implementation.