Error setting Toolbar as ActionBar

Question

I'm trying to replace the ActionBar of my app with a Toolbar but I can't because I can't use setSupportActionBar(). It says "setSupportActionBar() is undefined for the type MainActivity" even if MainActivity extends ActionBarActivity. I don't know what to do, any help? Do you need me to post my code?

EDIT: Now the code works but my app crashes on start and it says: "Attempt to invoke virtual method getTitle()". What do I miss?

EDIT2: Everything works I forgot I had a Fragment and because of that it gave me nullPointer

Answer 1

Now use :

import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
setSupportActionBar(toolbar);

XML :

android.support.v7.widget.Toolbar

Extends :

public class MainActivity extends AppCompatActivity