public class MainActivity extends AppCompatActivity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            LoginFragment loginFragment = new LoginFragment();
            FacebookSdk.sdkInitialize(this.getApplicationContext());


            FragmentManager fragmentManager = getFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.add(R.id.fragment_right_container, loginFragment);
            fragmentTransaction.commit();

            SessionManager sessionManager=new SessionManager();
            Log.d("Is Logged", "" + "" + AccessToken.getCurrentAccessToken());



/*            if(sessionManager.isLoggedIn()){
                Toast.makeText(this,"Logueado!",Toast.LENGTH_LONG).show();
            }*/

        }
    }

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             xmlns:tools="http://schemas.android.com/tools"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             tools:context=".LoginFragment">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:id="@+id/text_details"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text=""
        />

    <com.facebook.login.widget.LoginButton
        android:id="@+id/login_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="30dp"
        android:layout_marginBottom="30dp" />

</FrameLayout>

public class LoginFragment extends Fragment {

    private TextView textDetails;

   private CallbackManager callbackManager;

    private AccessTokenTracker tokenTracker;
    private ProfileTracker profileTracker;

    FacebookCallback<LoginResult> callback = new FacebookCallback<LoginResult>() {
    @Override
    public void onSuccess(LoginResult loginResult) {
        Log.d("Facebook-Callback", "onSuccess");
        AccessToken accessToken = loginResult.getAccessToken();
        Profile profile = Profile.getCurrentProfile();
        displayWelcomeMessage(profile);



    }

    @Override
    public void onCancel() {
        Log.d("Facebook-Cancel", "onCancel");
    }

    @Override
    public void onError(FacebookException error) {
        Log.d("Facebook-Error", "onCancel");
    }
};

    public LoginFragment() {
        // Required empty public constructor
    }


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        callbackManager=CallbackManager.Factory.create();

        setupTokenTracker();
        setupProfileTracker();

        tokenTracker.startTracking();
        profileTracker.startTracking();

    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_main, container, false);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        setupTextDetails(view);
        setupLoginButton(view);
    }

    @Override
    public void onResume() {
        super.onResume();
        Profile profile=Profile.getCurrentProfile();
        displayWelcomeMessage(profile);
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        callbackManager.onActivityResult(requestCode, resultCode, data);
    }


    @Override
    public void onStop() {
        super.onStop();
        tokenTracker.stopTracking();
        profileTracker.stopTracking();
    }


    //funciones de usuario

    private void displayWelcomeMessage(Profile profile){

        if(SessionManager.isLoggedIn()){
            textDetails.setText("Logged "+profile.getName());

        }else{
            textDetails.setText("Logged out");
        }

    }



    private void setupTextDetails(View view) {
        textDetails = (TextView) view.findViewById(R.id.text_details);
    }


    private void setupLoginButton(View view) {
        LoginButton buttonLogin = (LoginButton) view.findViewById(R.id.login_button);
        buttonLogin.setFragment(this);
        //I set up the permissions I want to ask for
        buttonLogin.setReadPermissions("user_friends");
        buttonLogin.registerCallback(callbackManager, callback);
    }

    //it's the callback function that listens everytime the profile of the user changes(change profile pic or whatever)
    private void setupProfileTracker() {

        profileTracker= new ProfileTracker() {
            @Override
            protected void onCurrentProfileChanged(Profile oldProfile, Profile newProfile) {
                Log.d("New Profile ", "" + newProfile);
                displayWelcomeMessage(newProfile);

            }

        };
    }

    //it's the callback function that listens everytime the token changes(When I lost connection I receive another token for example and the nthis function executes)
    private void setupTokenTracker() {

        tokenTracker= new AccessTokenTracker() {
            @Override
            protected void onCurrentAccessTokenChanged(AccessToken oldToken, AccessToken newToken) {
                //log in the console the new token
                Log.d("New token for User ", "" + newToken);
            }
        };

    }


}

public class SessionManager {
//check if it'slogged in to facebook

    String currentAccessToken=null;

    public void setAccessToken(String newToken){

        currentAccessToken=newToken;

    }

    public static boolean isLoggedIn() {
        AccessToken accessToken = AccessToken.getCurrentAccessToken();
        //Log.d("access token facebook",""+accessToken);
        return accessToken != null;
    }
}