如何在不同片段/活动中在android中维护会话？

Question

在使用SharedPreferences登录期间，我具有用于会话管理的此代码。该代码在登录期间可完美运行，但是当我在另一个片段/活动中使用它时，它将不再起作用。我收到错误“尝试在空对象引用上调用虚拟方法'void android.widget.TextView.setText（java.lang.CharSequence）'”。

有人可以帮助我正确地调用sessionmanagement对象吗？这是我的代码

SessionManagement.java

public class SessionManagement {

//URL to our login.php file
public static final String LOGIN_URL = "http://10.0.2.2:63343/login-test-session/login.php?";

//Keys for email and password as defined in our $_POST['key'] in login.php
public static final String KEY_EMAIL = "email";
public static final String KEY_PASSWORD = "password";

//If server response is equal to this that means login is successful
public static final String LOGIN_SUCCESS = "success";

//Keys for Sharedpreferences
//This would be the name of our shared preferences
public static final String SHARED_PREF_NAME = "themoneygerapp";

//This would be used to store the email of current logged in user
public static final String EMAIL_SHARED_PREF = "email";

//We will use this to store the boolean in sharedpreference to track user is loggedin or not
public static final String LOGGEDIN_SHARED_PREF = "loggedin";

ExpensesView.java（片段）

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_expenses_view, container, false);
    profiletest = (TextView) view.findViewById(R.id.txtProfileExpenses);
    SharedPreferences sharedPreferences = getActivity().getApplicationContext().getSharedPreferences(SessionManagement.SHARED_PREF_NAME, Context.MODE_PRIVATE);
    String email = sharedPreferences.getString(SessionManagement.EMAIL_SHARED_PREF,"Not Available");
    profiletest.setText("Expenses for user: " + email);
    loadExpenses();
    return view;
}