Common Data between MIDlets

[andybeeeeee]

Hi

I'm creating an application that gets a users position from a gps and uses it to perform different tasks. The way i was going to perform these tasks was to create a midlet suite with each of the tasks as a different MIDlet and pass the data from the gps, which is retrieved in its own midlet, to the others.

What i need to know is, is this possible? I've heard that you can use a record store and the rms api to have common data between different midlets in a suite, but would this work and is it a bit of an overkill? is there an easier way of doing this that i'm not seeing?

thanks
Andy

[juarezjunior]

Hi Andy,

I don't think sharing record stores is an overkill. This capability was introduced in MIDP 2.0 and it's useful.

BR

[andybeeeeee]

thanks alot for the answer! i'll try this, but i have a feeling i'll be abck with more questions....

[andybeeeeee]

I found an example class for creating my record store and i implemented it in this class:

import javax.microedition.rms.*;
import java.util.Enumeration;
import java.util.Vector;
import java.io.*;

public class PosDB {
   public RecordStore recordStore = null;
   public PosDB() {}

   // Open a record store with the given name
   public PosDB(String fileName) {
      try {
        recordStore = RecordStore.openRecordStore(fileName, true);
      } catch(RecordStoreException rse) {
        rse.printStackTrace();
      }
   }

   // Close the record store
   public void close()
	    throws RecordStoreNotOpenException,
                       RecordStoreException {
        if (recordStore.getNumRecords() == 0) {
            String fileName =
                           recordStore.getName();
            recordStore.closeRecordStore();
            recordStore.deleteRecordStore(
                                      fileName);
        } else {
            recordStore.closeRecordStore();
        }
    }

   // Add a new record (position)
   // to the record store
   public synchronized void addNewPos(String record) {
     
    byte[] rec = record.getBytes();

    try
    {
      recordStore.addRecord(rec, 0, rec.length);
    }
    catch (Exception e)
    {
      System.out.println(e);
      e.printStackTrace();
    }
  }


    // Enumerate through the records.
    public synchronized RecordEnumeration enumerate() throws RecordStoreNotOpenException {
       return recordStore.enumerateRecords(null, null, false);
    }
    
    public synchronized byte[] getPos(int number){
      byte[] recData = new byte[2];
      try
      {
        if (recordStore.getRecordSize(number) > recData.length)
          recData = new byte[recordStore.getRecordSize(number)];
        recData = recordStore.getRecord(number);
                      
      }
      catch (Exception e)
      {
        System.out.println(e);
        e.printStackTrace();
      }
      return recData;
    }
}

now i think this should be correct for the basic functions of adding to the database etc, so in another class i write

public void addToDatabase(){
      try{
       db = new PosDB("positions");
     } catch (Exception e){}
     try {
      db.addNewPos(splitData[2]+splitData[3]);
    }catch(Exception e) {}
     try{
       db.addNewPos(splitData[4]+splitData[5]);
     }catch(Exception e) { }
     try {
        db.close();
      } catch(Exception e) {}
    return;
    }

this should be right yes?

anyway, i then try to output the contents of records 1 and 2 to the screen ina test midlet that's part of my midlet suite:

public void startApp() throws MIDletStateChangeException{
    boolean b;
    try{
        db = new PosDB("positions");
      } catch (Exception e){}
      positiona = db.getPos(1);
      for(int i=0; i<positiona.length; i++){
        position1+=( char )positiona[ i ];
      }

      positionb = db.getPos(2);
      for(int j=0; j<positionb.length; j++){
       position2+=( char )positionb[ j ];
     }
      display = Display.getDisplay(this);
      display.setCurrent(form);
      form.addCommand(exitCommand);
      
      form.append("position 1:");
      form.append(position1 + "\n");
      form.append("position 2:");
      form.append(position2 + "\n");
      try{
        db.close();
      }
      catch(Exception e){
        System.out.println(e);
      }

but all i get coming out is null. for the life of me i can't figure out why this is happening, i'd normally put in some println statements to make sure everything's being called and data is being save etc, but i cant do that on a moble device and i dont think i can use bluetooth on the emulator... this is my first mobile application and it's abit tough!

can anyone see where i'm going wrong?
sorry for the mammouth post!!!
Andy