Android facebook sdk 4：检查用户是否已登录

Question

I'm facing a problem by using new facebook sdk. On my app, i've used old sdk, and everything works fine, but now something doesn't work well. I have a login FragmentActivity that check if user was already logged in in the past, so open app principal activity. If user is not logged in, activity show a fragment with login options (and one option is to log in with facebook). Fragment contains facebook login button, as described on documentation:

 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.choose_access_type, container,
            false);
    fb_button = (LoginButton) view.findViewById(R.id.fb_button);
    fb_button.setFragment(this);
    fb_button.setReadPermissions(Arrays.asList("public_profile",
            "user_friends"));
    LoginManager.getInstance().logInWithPublishPermissions(this, Arrays.asList("publish_actions"));
    callbackManager = CallbackManager.Factory.create();

    fb_button.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            //launche main activity
        }

        @Override
        public void onCancel() {
            // App code TODO
            Log.i("LOGINAFRAGMENT", "session cancel");
        }

        @Override
        public void onError(FacebookException exception) {
            // App code TODO
            Log.i("LOGINAFRAGMENT", "session error");
        }
    });

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

and this is code of FragmentActivity. This activity should check if user is already connected or not:

FacebookSdk.sdkInitialize(this.getApplicationContext());
 AccessToken fb_token = AccessToken.getCurrentAccessToken();
if(fb_token != null) {
    //already connected, launch activity
} else {
    //show fragment with login button
}

Now, also if user logged in the past, when I call getCurrentAccessToken I obtain always null, so fragment is showed, facebook detect that user was logged in, and main activity is launched. How can I check directly from FragmentActivity if user was already logged in?

Answer 1

You can track if token changed by following:`

accessTokenTracker=new AccessTokenTracker() {
            @Override
            protected void onCurrentAccessTokenChanged(AccessToken oldAccessToken, AccessToken currentAccessToken) {
                updateWithToken(currentAccessToken);
            }
        };`

then use following method to update the current token:

     private void updateWithToken(final AccessToken currentAccessToken) {
//start next activity if user is already logged in

//                    Intent i = new Intent(MainActivity.this,ProfilePictureActivity.class);
                   startActivity(i);

                 finish();


        } else {
              // redirect to login activity

                    Intent i = new Intent(MainActivity.this, login.class);
                    startActivity(i);

                    finish();

        }
    }
}

call updateWithToken(AccessToken.getCurrentAccessToken()); after sdk initialization