java - How to reverse scroll through SQLITE database table at the top of the table -

i storing messages chat group in table dedicated group.

now, time open group in listview, displays last n messages using code:

    public arraylist<post> getrecentposts(int numofmessagesgottenalready,int numofmessagesneeded) {             sqlitedatabase db = this.getreadabledatabase();  cursor res = db.rawquery("select * "+room_table_name+ " limit "+numofmessagesneeded +                     " offset (select count(*) "+room_table_name+")-"+                     (numofmessagesgottenalready + numofmessagesneeded)+";", null);              res.movetofirst();             arraylist<post>posts = new arraylist<>();             while (!res.isafterlast()) {                 posts.add(post.parsejsontopost(                         res.getstring(res.getcolumnindex(rooms_column_json))) );                 res.movetonext();             }              if (!res.isclosed()) {                 res.close();             }             return posts;         } 

any time need load more messages group,i call above method supplies number of messages loaded first argument , number of messages need loaded second argument.

the method works (or think), loading messages bottom of table upwards of course. there hitch.

when gets top of table i.e. offset=0and method called again, offset becomes negative , keeps loading earliest messages @ top of table specified @ https://www.sqlite.org/lang_select.html.

i want when offset evaluates value less zero, no value returned in cursor.

how modify expression achieve please?

okay, solved problem using 2 separate queries:

i wrapped whole process described below in transaction.

i first obtained number of messages on table. checked using java code if there more messages loaded..and based on result, loaded more messages. able detect if had gotten top of table , write necessary code return empty list in event:

here code: can used implement whatsapp's load earlier messages feature...where loading done sqlite table.

    /**      * useful loading chatroom has messages loaded bottom of      * table. allows 'load more' messages(just number needed) without loading      * whole chatroom.      * @param numofmessagesgottenalready number of messages room has already.      * @param numofmessagesneeded number of messages load more.      * @return arraylist of messages loaded in pagination style..from bottom time.      */     public arraylist<post> getrecentposts(int numofmessagesgottenalready,int numofmessagesneeded) {         sqlitedatabase db = this.getreadabledatabase();         int add = numofmessagesgottenalready + numofmessagesneeded;           boolean success = true;         try {             db.begintransaction();              cursor res = db.rawquery("select count(*) "+room_table_name , null);             res.movetofirst();              int count = res.getint(0);             if (!res.isclosed()) {                 res.close();             }              log.e("table row count", count + "");              log.e("add", add + "");              if(count >= numofmessagesgottenalready) {                 cursor set = db.rawquery("select * " + room_table_name + " order " + rooms_column_id +                         " asc limit " + numofmessagesneeded +                         " offset ( " + (count - add) + " )"                         , null); set.movetofirst();                 arraylist<post>posts = new arraylist<>();                 try {                     while (!set.isafterlast()) {                         posts.add(post.parsejsontopost(                                 set.getstring(set.getcolumnindex(rooms_column_json))));                         set.movetonext();                     }                 }                 catch (exception e){return posts;}                 if (!set.isclosed()) {                     set.close();                 }                 return posts;             }              db.settransactionsuccessful();             success = true;         }         catch (sqliteexception e){             e.printstacktrace();             success = false;         }         {             db.endtransaction();         }  return new arraylist<post>();     } 

thanks!