Question

Following on from my previous question about tables I am trying to create additional tables on my database in Android.

Basically, I would like a database to be created which is done so by this code:

 public void onCreate(SQLiteDatabase db) {
        db.execSQL(DATABASE_CREATE);
    }

Then when a user adds an account I would like a table added with the name of the account the user entered. I try to call the createTable() method I created.

 public void createAccount(String account) {
        DATABASE_TABLE = account;
        db.execSQL(TABLE_CREATE);
        System.out.println(DATABASE_NAME);      
}

But the db doesn’t work as eclipse cannot find the variable. I try mDb which is my SQLiteDatabase but I get a null pointer exception.

*Edit*

I really can’t get my head around the database. I am using the For Dummies book and a Database helper but from where I am at now I feel a lot of the code is done behind the scenes and it is hard to follow.

This is part of my database class:

private static class DatabaseHelper extends SQLiteOpenHelper {

    DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }


    public void onCreate(SQLiteDatabase db) {
        System.out.println(DATABASE_TABLE);
        db.execSQL(TABLE_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                + newVersion + ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
        onCreate(db);
    }

    public void createAccount(String account) {
        DATABASE_TABLE = account;
        /*   SQLiteDatabase db = this.getWritableDatabase();
        db.execSQL("create table long ("
                + KEY_ROWID + " integer primary key autoincrement, "
                + KEY_DESCRIPTION + " text not null, " 
                + KEY_DEBIT + " text not null);");   
    }       
}

At the bottom of the class I have

public void changeDatabase(String account) {
    DATABASE_TABLE = account;
    mDbHelper.createAccount(account);
}

which is called upon from my createAccount class.

I am getting a null point exception.

Answer 1

This is without seeing your code…

I’m guessing you’ve inherited / extended from one of the SQLite Classes.

you see how you’ve implemented onCreate() and are provided the database as a parameter,

if you create a new function, like that createAccount function you need to get a handle of the db as follows:-

 public void createAccount(String account) {
    DATABASE_TABLE = account;
    SQLiteDatabase db = this.getWritableDatabase();
    db.execSQL(TABLE_CREATE);
    System.out.println(DATABASE_NAME);      
}

• Anthony