facebook session expires in android

i am using facebook api in my android project

{"error":{"type":"OAuthException","message":"Error validating access token:
Session has expired at unix time 1307350800.
The current unix time is 13073528开发者_开发百科70."}}

My session expires....after a while....i want it as session never...expires

expecting piece a piece code..so that session never endsup

am using this for authorizing

    facebook.authorize(SignIn.this,
                    new DialogListener() {

You have to request the offline permission when the user signs in to get a token that doesn't expire.

getFacebookApi().authorize(this, new String[]{"offline_access"}, CONSTANT_ID, myDialogListener);

hope this helps!