The EventSharingMIDlet class is the MIDlet main
class. This class handles the following tasks:
Common startup events such as setting the default Display
Displaying the start-up screen as the MIDlet launches
Common MIDlet lifecycle tasks
Launching the EventCreationForm as the MIDlet
starting view
Displaying error messages using the ErrorScreen
To implement the EventSharingMIDlet class:
Create the EventSharingMIDlet.java class file.
Import the required packages.
import java.io.*; import javax.microedition.io.*; import javax.microedition.lcdui.*; import javax.microedition.midlet.*; import javax.wireless.messaging.*;
Set EventSharingMIDlet to extend MIDlet and
implement MessageListener. Create the required variables
(note the hardcoded default port and the SMS prefix) and the class
constructor.
public class EventSharingMIDlet extends MIDlet implements MessageListener {
private final static int DEFAULT_PORT = 6553;
private final static String SMS_PREFIX = "sms://:";
private final Image logo;
private final EventCreationForm mainScreen;
private int port;
private MessageConnection conn;
private OperationsQueue queue = new OperationsQueue();
private final Display display;
public EventSharingMIDlet() {
// init basic parameters
logo = makeImage("/logo.png");
try {
port = Integer.parseInt(getAppProperty("port"));
} catch (Exception e) {
// in case the property is missing or with a wrong format
port = DEFAULT_PORT;
}
ErrorScreen.init(logo, Display.getDisplay(this));
mainScreen = new EventCreationForm(this, port);
display = Display.getDisplay(this);
}Create a method
for sending a message. The message is sent through a connection instance
created with MessageConnection. Note the correct data
types. The message content is sent as a byte[] data
type and the destination address includes an sms:// prefix.
void sendMessage(String number, byte[] text) {
showMessage("Sending event " + "to number " + number);
if (conn != null) {
try {
// create a new message
BinaryMessage requestSMS = (BinaryMessage)conn.newMessage(MessageConnection.BINARY_MESSAGE);
String address = new StringBuffer("sms://").append(number).append(":").append(port).toString();
requestSMS.setAddress(address);
requestSMS.setPayloadData(text);
conn.send(requestSMS);
} catch (IOException e) {
showMessage(e.getMessage());
} catch (SecurityException e) {
showMessage(e.getMessage());
}
}
}Handle the application
startup duties in the startApp method. Use system
property calls to verify that the PIM API is available on the device
and to display the start-up screen while the MIDlet loads.
public void startApp() {
Displayable current = Display.getDisplay(this).getCurrent();
if (current == null) {
// check that the API is available
boolean isAPIAvailable = (System.getProperty("microedition.pim.version") != null);
// shows splash screen
StringBuffer splashText = new StringBuffer(getAppProperty("MIDlet-Name")).append("\n")
.append(getAppProperty("MIDlet-Vendor")).append(isAPIAvailable ? "" : "\nPIM API not available");
//Alert splashScreen = new Alert(null, splashText.toString(), logo, AlertType.INFO);
//splashScreen.setTimeout(3000);
if (!isAPIAvailable) {
//display.setCurrent(splashScreen, mainScreen);
display.setCurrent(mainScreen);
} else {
//display.setCurrent(splashScreen, mainScreen);
display.setCurrent(mainScreen);Check
if the class has been activated by an incoming message through PushRegistry. Continue to receive the message, display it, and close the
connection after finished.
// List connections from PushRegistry
String smsConnections[] = PushRegistry.listConnections(true);
// Chech the connections. We'll assume only one is of interest
for (int i = 0; i < smsConnections.length; i++) {
if (smsConnections[i].startsWith(SMS_PREFIX)) {
try {
conn = (MessageConnection) Connector.open(smsConnections[i]);
BinaryMessage incomingMessage = (BinaryMessage)conn.receive();
showIncomingMessage(incomingMessage);
conn.close();
} catch (IOException e) {
showMessage(e.getMessage());
} catch (SecurityException e) {
showMessage(e.getMessage());
}
}
}
// Build the connection string
String connection = SMS_PREFIX + port;
try {
// Initiate the connection and add listener
conn = (MessageConnection) Connector.open(connection);
conn.setMessageListener(this);
} catch (IOException e) {
showMessage(e.getMessage());
} catch (SecurityException e) {
showMessage(e.getMessage());
}
}
} else {
Display.getDisplay(this).setCurrent(current);
}
}Create the rest
of the standard lifecycle methods: pauseApp and destroyApp.
public void pauseApp() {
}
public void destroyApp(boolean unconditional) {
try {
// Close the connection on exit
if (conn != null) {
conn.close();
}
} catch (IOException e) {
// Ignore since we are closing anyway
}
queue.abort();
}Create methods
to notify the MIDlet when an inbound message is arriving through a MessageConnection and to display the IncomingEventForm when incoming event messages are received.
// Asynchronous callback for inbound message.
public void notifyIncomingMessage(MessageConnection conn) {
if (conn == this.conn && conn != null) {
try {
// Create a ReceiveScreen upon message removal
BinaryMessage incomingMessage = (BinaryMessage) conn.receive();
showIncomingMessage(incomingMessage);
} catch (IOException e) {
showMessage(e.getMessage());
} catch (SecurityException e) {
showMessage(e.getMessage());
}
}
}
void showIncomingMessage(BinaryMessage msg) {
display.setCurrent(new IncomingEventForm(this, msg));
}Create the rest
of the MIDlet methods. These include methods for displaying errors
with an ErrorScreen, a contacts list callback, and
an image creation method called earlier in the class.
void showMessage(String message) {
ErrorScreen.showError(message, mainScreen);
}
void showMessage(String message, Displayable mainScreen) {
ErrorScreen.showError(message, mainScreen);
}
// adds an operation the queue
void enqueueOperation(Operation operation) {
queue.enqueueOperation(operation);
}
// shows the main screen
void showMain() {
display.setCurrent(mainScreen);
}
// shows the contacts list screen
void showContactsList() {
display.setCurrent(new ContactListForm(EventSharingMIDlet.this));
}
// callback from contacts list when a particular
// telephone number has been selected
void contactSelected(String telephoneNumber) {
mainScreen.setTargetPhoneNumber(telephoneNumber);
showMain();
}
// loads a given image by name
static Image makeImage(String filename) {
Image image = null;
try {
image = Image.createImage(filename);
} catch (Exception e) {
// use a null image instead
}
return image;
}
}Now that you have implemented the MIDlet main class, implement an operations queue for sending and receiving event messages.