How do I check if the user has already logged in once?

Question

When the user presses the "login with facebook" button for the first time, the application asks for permission and returns the "Gave" dialog, however if I login and try to login again error appears, then I have to delete the permission in the application to be able to do again, how do I check if the user has already registered once?

import android.app.AlertDialog;
import android.content.Intent;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.facebook.AccessToken;
import com.facebook.AccessTokenTracker;
import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.FacebookSdk;
import com.facebook.appevents.AppEventsLogger;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;

public class LoginFacebook extends Fragment {

    private LoginButton loginButton;
    private CallbackManager callbackManager;
    private AccessTokenTracker accessTokenTracker;
    private AccessToken accessToken;
    private Fragment1 fragment1;

    @Override
    public View onCreateView(
            LayoutInflater inflater,
            ViewGroup container,
            Bundle savedInstanceState) {
        FacebookSdk.sdkInitialize(getContext());

        callbackManager = CallbackManager.Factory.create();
        final View view = inflater.inflate(R.layout.loginfacebook, container, false);


        loginButton = (LoginButton) view.findViewById(R.id.loginfacebook);
        loginButton.setReadPermissions("email");
        // If using in a fragment
        loginButton.setFragment(this);
        // Other app specific specialization

        // Callback registration
        loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                AlertDialog.Builder dlg = new AlertDialog.Builder(getContext());
                dlg.setMessage("deu"+loginResult.getAccessToken().getUserId());
                dlg.setNeutralButton("ok",null);
                dlg.show();



            }

            @Override
            public void onCancel() {
                AlertDialog.Builder dlg = new AlertDialog.Builder(getContext());
                dlg.setMessage("cancelou");
                dlg.setNeutralButton("ok",null);
                dlg.show();
            }

            @Override
            public void onError(FacebookException exception) {
                AlertDialog.Builder dlg = new AlertDialog.Builder(getContext());
                dlg.setMessage("deu erro");
                dlg.setNeutralButton("ok",null);
                dlg.show();

            }
        });


        accessTokenTracker = new AccessTokenTracker() {
            @Override
            protected void onCurrentAccessTokenChanged(
                    AccessToken oldAccessToken,
                    AccessToken currentAccessToken) {
                // Set the access token using
                // currentAccessToken when it's loaded or set.
            }
        };
        // If the access token is available already assign it.
        accessToken = AccessToken.getCurrentAccessToken();




        return view;

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



}