SectionsPagerAdapter Error

package com.erinkabbash.ribbit;

import java.util.Locale;

import android.app.Fragment;
import android.app.FragmentManager;
import android.content.Context;
import android.support.v13.app.FragmentPagerAdapter;
import android.support.v4.app.ListFragment;

/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentPagerAdapter {

    protected Context mContext;

    public SectionsPagerAdapter(Context context, FragmentManager fm) {
        super(fm);
        mContext = context;
    }

    @Override

    public ListFragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class
        // below).

        return new InboxFragment(); 
    }

    @Override
    public int getCount() {
        return 2;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Locale l = Locale.getDefault();
        switch (position) {
            case 0:
                return mContext.getString(R.string.title_section1).toUpperCase(l);
            case 1:
                return mContext.getString(R.string.title_section2).toUpperCase(l);

        }
        return null;
    }
}