Accessing facebook sessions in different Activities

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http://stackoverflow.com – I am using different activities for login, facebook friend sync and for post. I am logging in using LoginButton. Once the login is done, I am launching a new activity and trying to access the previous session using Session session = Session.getActiveSession(); but it always returns null. I wanted to access the previous session in different activities without facebook login every time. Please note am using facebook sdk 3.0 (HowTos)