Implementation

For information about the design and functionality of the MIDlet, see section Design.

The MIDlet consists of a single class, ProximityReminder.

To create the MIDlet:

1. Create the ProximityReminder.java class file.

2. Import the required classes and packages, initialize the UI elements and Commands, and define the standard startApp, pauseApp, and destroyApp methods without any additional configurations.

   import javax.microedition.midlet.*;
   import javax.microedition.lcdui.*;
   import javax.microedition.location.*;
   import javax.microedition.lcdui.Alert;
   import javax.microedition.lcdui.AlertType;
   
   public class ProximityReminder
       extends MIDlet
       implements CommandListener, ProximityListener {
   
       private Alert timedAlert;
       private Displayable currentDisplay;
       private Command ExitCmd;
       private Command OptionsCmd;
       private Form form;
   
       // Menu
       private List OptionsMenu;
       private String error = "";
       private Location currentLocation = null;
   
       public void startApp() {
           initialize();
       }
   
       public void pauseApp() {
           //Nothing to do
       }
   
       public void destroyApp(boolean unconditional) {
           //Nothing to do
       }

3. Add a Form and two Commands when the MIDlet is started.

       private void initialize() {
           getDisplay().setCurrent(get_form());
           SetCurrDisplay(get_form());
           currentDisplay = getDisplay().getCurrent();
       }
   
       public Form get_form() {
           if (form == null) {
               form = new Form(null);
               form.addCommand(get_OptionsCmd());
               form.addCommand(get_exitCmd());
           }
   
           form.setTicker(new Ticker("PROXIMITY REMINDER"));
           form.setCommandListener(this);
   
           return form;
       }
   
       // ...
   
       public Display getDisplay() {
           return Display.getDisplay(this);
       }
   
       boolean SetCurrDisplay(Displayable currDisp) {
           if (currDisp == null) {
   
               if (currentDisplay == null)
                   return false;
               else
                   currDisp = currentDisplay;
           }
           else {
               currentDisplay = currDisp;
           }
   
           getDisplay().setCurrent(currentDisplay);
           return true;
       }
   
       public void exitMIDlet() {
           destroyApp(true);
           notifyDestroyed();
       }

4. Handle the location detection and exit Commands.

       // COMMANDS
       public Command get_exitCmd()
       {
           if (ExitCmd == null) {
               ExitCmd = new Command("Exit", Command.EXIT, 1);
           }
   
           return ExitCmd;
       }
   
       // COMMANDS
       public Command get_OptionsCmd()
       {
           if (OptionsCmd == null) {
               OptionsCmd = new Command("Options", Command.OK, 1);
           }
   
           return OptionsCmd;
       }
   
       public List get_Options() {
           if (OptionsMenu == null) {
               OptionsMenu = new List("Select Option", Choice.IMPLICIT,
                       new String[] { "Add Proximity to Current Location",
                               "Cancel" }, new Image[] { null, null });
   
               OptionsMenu.setCommandListener(this);
               OptionsMenu.setSelectedFlags(new boolean[] { true, false });
           }
           return OptionsMenu;
       }
   
       public void commandAction(Command command, Displayable displayable) {
           if (displayable == form) {
               if (command == ExitCmd) {
                   exitMIDlet();
               }
               else if (command == OptionsCmd) {
                   getDisplay().setCurrent(get_Options());
               }
           }
   
           if (displayable == OptionsMenu) {
               if (command == OptionsMenu.SELECT_COMMAND) {
                   switch (OptionsMenu.getSelectedIndex()) {
                       case 0:
                           new Thread(new Runnable() {
                               public void run() {
                                   getCurrentLocation();
                               }
                           }).start();
                           // flow through
                       case 1:
                           getDisplay().setCurrent(get_form());
                       break;
                   }
               }
               else if (command == ExitCmd) {
                   exitMIDlet();
               }
           }
       }

5. Create methods for detecting the current location coordinates and for adding a ProximityListener to listen to changes in the device location.

       // fetches the current location and adds the current location to proximity
       void getCurrentLocation() {
           try {        
               // Get the provider with default criteria
               LocationProvider provider = LocationProvider.getInstance(null);
   
               if (provider != null) {
                   // fetch the current location
                   currentLocation = provider.getLocation(-1);
               }
           }
           catch (Exception e) {
               addError(e);
           }
   
           addproximity();
       }
   
       // Adds the current Location for Proxmity Updates
       void addproximity() {
           try {
               if (currentLocation != null) {
                   // get the current latitude, langitude and altitude
                   float alt = currentLocation.getQualifiedCoordinates().getAltitude();
                   double lat = currentLocation.getQualifiedCoordinates().getLatitude();
                   double lon = currentLocation.getQualifiedCoordinates().getLongitude();
   
                   Coordinates cord1 = new Coordinates(lat, lon, alt);
   
                   // Adds the current coordinates for proximity updates when the
                   // device is within the proximity radius of 500 meters
                   LocationProvider.addProximityListener(this, cord1, 500.0f);
               }
           }
           catch (SecurityException e) {
               addError(e);
           }
           catch (Exception e) {
               addError(e);
           }
       }
   
       public void addError(Exception e) {
           e.printStackTrace();
           error += e.getMessage() + "\n";
       }

6. Use the ProximityListener.monitoringStateChanged method to listen when the state of the proximity monitoring has changed.

       // This function will be called when the monitoring state changes
       public void monitoringStateChanged(boolean aState)
       {
           if (aState) {
               timedAlert = new Alert("Proximity Status", " Active", null,
                       AlertType.INFO);
               timedAlert.setTimeout(5000);
           }
           else {
               timedAlert = new Alert("Proximity Status", " NOT Active", null,
                       AlertType.INFO);
               timedAlert.setTimeout(5000);
           }
       }

7. Create a proximityEvent for handling the situations when the device proximity event is activated. Display the location information from the event to the user using an Alert.

       // This function will be called when the Proximity event fires
       public void proximityEvent(Coordinates aCord, Location aLoc) {
           // Displays the information using an alert
           timedAlert = new Alert("Proximity Update",
                   "You are now near Location: lat = " + aCord.getLatitude()
                           + " lon =" + aCord.getLongitude(), null, AlertType.INFO);
           timedAlert.setTimeout(5000);
           currentDisplay = getDisplay().getCurrent();
           getDisplay().setCurrent(timedAlert, currentDisplay);
       }
   }