Facebook wall post from multiple pages

I have been trying to make wall post from multiple pages but when i try to make post from other pages except original facebook page, it is giving me an exception of java.lang.NullPointerException

The method i am calling and created in a Facebook page

public void postOnWall(String msg) {
        Log.d("Tests", "Testing graph API wall post");
         try {
                String response = mFacebook.request("me");
                Bundle parameters = new Bundle();
                parameters.putString("message", msg);
                parameters.putString("description", "test test test");
                response = mFacebook.request("me/feed", parameters, 
                        "POST");
                Log.d("Test开发者_StackOverflow社区s", "got response: " + response);
                if (response == null || response.equals("") || 
                        response.equals("false")) {
                   Log.v("Error", "Blank response");
                }
         } catch(Exception e) {
             e.printStackTrace();
         }
    }

and code to call this method.

try {

                    mFacebookObj.postOnWall("Add poi");

                } catch(Exception e){
                    e.printStackTrace();
                }

both are activity classes.

Now can anyone tell me how shall i call this method from outside this page and make post over facebook wall

The answer is, to make wall post from from multiple pages, just restore values of access_token and token_expire value in faceook object.. and then use mFacebook.request(...); That works as Facebook object needs to have access token and access token expire value provided by facebook itself in response given at the time of login with facebook