android - NullPointerException sqlite -

i trying store oauth tokens in database using sqlite. when creating new row, getting "nullpointerexception." receiving token instagram (it works if storing in shared prefs), fails if try , store in sqlite.

my tokendatasource:

public class tokendatasource  {       // database fields       private sqlitedatabase database;       private dbhelper dbhelper;       private string[] allcolumns = { dbhelper.column_id,           dbhelper.column_token };        public void close(){            dbhelper.close();       }        public void open() throws sqlexception{            database = dbhelper.getwritabledatabase();       }        public tokendatasource(context context){            dbhelper = new dbhelper(context);       }        public void deleteinstagramtoken(instagramtoken token)       {           long id = token.getid();           database.delete(dbhelper.table_insta_tokens, dbhelper.column_id                     + " = " + id, null);       }        public instagramtoken createinstagramtoken(string token)        {             contentvalues values = new contentvalues();             values.put(dbhelper.column_token, token);             long insertid = database.insert(dbhelper.table_insta_tokens, null,                 values);             cursor cursor = database.query(dbhelper.table_insta_tokens,                 allcolumns, dbhelper.column_id + " = " + insertid, null,                 null, null, null);             cursor.movetofirst();             instagramtoken newtoken = cursortotoken(cursor);             cursor.close();              return newtoken;       }        public list<instagramtoken> getallinstagramtokens()       {           list<instagramtoken> tokens = new arraylist<instagramtoken>();            cursor cursor = database.query(dbhelper.table_insta_tokens,                     allcolumns, null, null, null, null, null);           cursor.movetofirst();            while (!cursor.isafterlast())           {               instagramtoken token = cursortotoken(cursor);               tokens.add(token);               cursor.movetonext();           }            cursor.close();            return tokens;       }        private instagramtoken cursortotoken(cursor cursor)       {           instagramtoken token = new instagramtoken();            token.setid(cursor.getlong(0));           token.settoken(cursor.getstring(1));            return token;       } } 

my dbhelper:

public class dbhelper extends sqliteopenhelper  {       public static final string table_insta_tokens = "insta_tokens";       public static final string column_id = "_id";       public static final string column_token = "token";        private static final string database_name = "status.db";       private static final int database_version = 1;        // database creation sql statement       private static final string database_create = "create table "           + table_insta_tokens + "(" + column_id           + " integer primary key autoincrement, " + column_token           + " text not null);";        public dbhelper(context context) {         super(context, database_name, null, database_version);       }        @override       public void oncreate(sqlitedatabase database) {         database.execsql(database_create);       }        @override       public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {         log.w(dbhelper.class.getname(),             "upgrading database version " + oldversion + " "                 + newversion + ", destroy old data");         db.execsql("drop table if exists " + table_insta_tokens);         oncreate(db);       } } 

the storeaccesstoken method:

public instagramsession(context context)  {     this.mctx = context;     sharedpref = context.getsharedpreferences(shared, context.mode_private);     editor = sharedpref.edit(); }  public void storeaccesstoken(string accesstoken, string id, string username, string name)  {     tokendatasource datasource = new tokendatasource(mctx);      editor.putstring(api_id, id);     editor.putstring(api_name, name);     editor.putstring(api_access_token, accesstoken);     editor.putstring(api_username, username);     editor.commit();      datasource.createinstagramtoken(accesstoken); } 

instead of have method stores in member class instance of sqlitedatabase should call dbhelper.getwritabledatabase() every time need access