Delete Persistent Object when app is Deleted in Blackberry

Question

I am using persistent object in blackberry to store config details specific to the app. Here is how I am implementing the class

public class Preferences implements Persistable
{
    private static  PersistentObject persistentObject = PersistentStore.getPersistentObject(0x2759d6ff72264bdbL);
    private static Hashtable tbl = new Hashtable();

    public static void storeLoginToken(String token)
    {
        token = removeCharAt(token,0);
        token = removeCharAt(token,token.length()-1);
        tbl.put("token", token);
        persistentObject.setContents(tbl);
        persistentObject.commit();
    }

    public static String getLoginToken()
    {
        Hashtable tbl = (Hashtable)persistentObject.getContents();
        try
        {
            String token = tbl.get("token").toString();
            System.out.println("Token = "+token);
            return token;
        }
        catch(Exception e)
        {
            return null;
        }

    }
}

But if I uninstall/delete the app these stored values are not getting deleted. When I installs the app for next time the app is fetching the old stored values.

How can i do this properly in blackberry? Thanks

Answer 1

Create a custom hashtable class like this

package com.myapp.items;


import net.rim.device.api.util.Persistable;

import java.util.*;

public class MyAppHashtable extends Hashtable implements Persistable{

}  

And change your code to

public class Preferences
{
    private static  PersistentObject persistentObject = PersistentStore.getPersistentObject(0x2759d6ff72264bdbL);
    private static MyAppHashtable tbl = new MyAppHashtable ();

    public static void storeLoginToken(String token)
    {
        token = removeCharAt(token,0);
        token = removeCharAt(token,token.length()-1);
        tbl.put("token", token);
        persistentObject.setContents(tbl);
        persistentObject.commit();
    }

    public static String getLoginToken()
    {
        MyAppHashtable tbl = (MyAppHashtable )persistentObject.getContents();
        try
        {
            String token = tbl.get("token").toString();
            System.out.println("Token = "+token);
            return token;
        }
        catch(Exception e)
        {
            return null;
        }

    }
}

This is so that we adhere to the following info from RIM

The BlackBerry persistence model

When you use the BlackBerry persistence model, data is only deleted if the store contains data that belongs to the removed application.

For example, if an application stores an object with a package called com.mycompany.application.storage and no other application on the BlackBerry smartphone makes reference to the package, the persistent store and the removed application are deleted.

The same is true if the object is wrapped in a container such as a Vector. Even if only one of the elements of the Vector has a package name that is not used by other applications, the entire Vector is removed from the persistent store.

Note: If the application does not store any objects with an identifying package structure, (for example, an application that stores java.util.Vector or javax.microedition.location.AddressInfo objects), the application should create and use a class that extends Vector in order to identify that Vector belongs to the given application. When you store this Vector, which is identified uniquely by its package, you guarantee that the data is removed from the persistent store when the application is removed.

This info is from here