Login to facebook account without exiting app using facebook client API

I want to provide the user the option of posting to his facebook wall ,through my app. Inorder to achieve this , for facebook authentication and posting action I have used the facebook & facebook client API's provided by microsoft (their latest alpha version). I could also able to achieve the process of posting also using the API methods. The main problem , was on completion of Facebook authentication my app is getting relaunched newly , losing its existing instance. Is there any alternative ways so that I can achieve my scenario without exiting the app.

my authentication code here below

Session.ActiveSession.LoginWithBehavior("email,public_profile,user_friends,publish_actions", FacebookLoginBehavior.LoginBehaviorWebViewOnly);

Please let me know if some alternatives are possible.

Thanks, Mawy