android - AccessToken.getCurrentAccessToken() is null -

i integrated facebook in app , getting proper token. if token exists assigns it, , if it's first time make request token. however, token not being received.

here code:

@override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         facebooksdk.sdkinitialize(this.getapplicationcontext());         callbackmanager = callbackmanager.factory.create();          accesstokentracker = new accesstokentracker() {             @override             protected void oncurrentaccesstokenchanged(                     accesstoken oldaccesstoken,                     accesstoken currentaccesstoken) {                 // set access token using                 // currentaccesstoken when it's loaded or set.             }         };         // if access token available assign it.         accesstoken = accesstoken.getcurrentaccesstoken();         setcontentview(r.layout.activity_signup); 

were able solve this? have noticed graphrequest.newmerequest not delete old session data, return null response in oncomplete. alternative, use graphrequest.newgraphpathrequest(accesstoken, "/me"...), similar results.