Megandi Megandi - 4 months ago 12
Android Question

ERROR: on a null object reference

I don't know what's wrong in my code

this is my Fragment class

package com.example.gandi.symanlub;


/**
* A simple {@link Fragment} subclass.
*/
public class Reminder extends Fragment {

Button btnubah, btnkeluar;
SessionManager session;

View rootview;



@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
rootview = inflater.inflate(R.layout.fragment_reminder, container, false);

btnkeluar = (Button)rootview.findViewById(R.id.btnlogout);
btnkeluar.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
session.logoutUser();
}
});

return rootview;

}

}




and this is my SessionManager.java

package com.example.gandi.symanlub;

@SuppressLint("CommitPrefEdits")
public class SessionManager {
// Shared Preferences
SharedPreferences pref;

// Editor for Shared preferences
SharedPreferences.Editor editor;

// Context
Context _context;

// Shared pref mode
int PRIVATE_MODE = 0;

// nama sharepreference
private static final String PREF_NAME = "Sesi";

// All Shared Preferences Keys
private static final String IS_LOGIN = "IsLoggedIn";
public static final String KEY_EMAIL = "email";
public static final String KEY_PASS = "pass";



// Constructor
public SessionManager(Context context){
this._context = context;
pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
editor = pref.edit();
}

/**
* Create login session
* */
public void createLoginSession(String email, String pass){
// Storing login value as TRUE
editor.putBoolean(IS_LOGIN, true);

editor.putString(KEY_EMAIL, email);
editor.putString(KEY_PASS, pass);
editor.commit();
}

/**
* Check login method wil check user login status
* If false it will redirect user to login page
* Else won't do anything
* */
public void checkLogin(){
// Check login status
if(!this.isLoggedIn()){
Intent i = new Intent(_context, Login.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
_context.startActivity(i);
//((Activity)_context).finish();
}

}

/**
* Get stored session data
* */
public HashMap<String, String> getUserDetails(){
HashMap<String, String> user = new HashMap<String, String>();

user.put(KEY_EMAIL, pref.getString(KEY_EMAIL, null));
user.put(KEY_PASS, pref.getString(KEY_PASS, null));

return user;
}

/**
* Clear session details
* */
public void logoutUser(){
editor.clear();
editor.commit();
}

public void hapussesi(){
editor.clear();
editor.commit();
}

public boolean isLoggedIn(){
return pref.getBoolean(IS_LOGIN, false);
}
}




the error when I run the project :

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.gandi.symanlub.SessionManager.logoutUser()' on a null object reference

Answer

You're getting an error because at this line you're calling:

session.logoutUser();

While session is null because it is not initialized anywhere. You need to add a line to initialize it before using it (you can do it in onCreateView, or in onAttach or anywhere you see fit):

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    session = new SessionManager(getActivity());

getActivity is used to pass a Context to your constructor, as I see it takes that parameter.

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