java - Android Facebook login callback -

i'm programming simple facebook login android app, i've configured sdk , added fb login button, i'm trying display in logcat facebook response seems if callback function not triggered.

this oncreate

protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     facebooksdk.sdkinitialize(getapplicationcontext());     setcontentview(r.layout.activity_main);     callbackmanager = callbackmanager.factory.create();      loginmanager.getinstance().registercallback(callbackmanager,             new facebookcallback<loginresult>() {                 @override                 public void onsuccess(loginresult loginresult) {                     // app code                     log.e("", string.valueof(loginresult));                 }                  @override                 public void oncancel() {                     // app code                 }                  @override                 public void onerror(facebookexception exception) {                     // app code                 }     }); } 

anyone can me? thank's

read guide. there's complete example can copy , paste.