Activity is not tied to Android.appActivity Manifest XML

I am having some problems with fragment in Android Studio. So basically this is my MainActivity:

public class MainActivity extends FragmentActivity {
final Context context = this;

ViewPager Tab;
TabPagerAdapter TabAdapter;
ActionBar actionBar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    TabAdapter = new TabPagerAdapter(getSupportFragmentManager());
    Tab = (ViewPager) findViewById(R.id.pager);
    Tab.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            actionBar = getActionBar();
            actionBar.setSelectedNavigationItem(position);
        }
    });
    Tab.setAdapter(TabAdapter);
    actionBar = getActionBar();
    // Enable Tabs on Action Bar
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    ActionBar.TabListener tabListener = new ActionBar.TabListener() {
        @Override
        public void onTabReselected(android.app.ActionBar.Tab tab,
                                    android.app.FragmentTransaction ft) {
        }

        @Override
        public void onTabSelected(android.app.ActionBar.Tab tab,
                                  android.app.FragmentTransaction ft) {
            // on tab selected show respected fragment view
            Tab.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabUnselected(android.app.ActionBar.Tab tab,
                                    android.app.FragmentTransaction ft) {
        }
    };

    // Add New Tab
    actionBar.addTab(actionBar.newTab().setText("Feedback")
            .setTabListener(tabListener));
    actionBar.addTab(actionBar.newTab().setText("History Log")
            .setTabListener(tabListener));


}
}

      

        
        
        
      

    

And then my other class, which is one of the tab code:

public class FeedbackMain extends Fragment {
View feedbackMainView;

public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    feedbackMainView = inflater.inflate(R.layout.activity_feedback_main,
            container, false);

    return feedbackMainView;
}
}

      

        
        
        
      

    

And then my manifest:

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".FeedbackMain"
        android:label="@string/title_activity_feedback_main" >
    </activity>

      

        
        
        
      

    

However, I get red lines under .FeedbackMain and an error message:

.FeedbackMain is not assignable to 'android.app.Activity'

      

        
        
        
      

    

I was wondering why this is so? This works great with Android development tools, but then when I switched to Android Studio it happens.

Thanks in advance.

Edit

xml file for mainActivity:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.view.ViewPager
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent" />

      

        
        
        
      

    

style.xml:

<resources>

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
</style>

</resources>