the sections pager activity has problems that I don't understand!!!

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

// ....

new SectionsPagerAdapter( getSupportFragmentManager() );

package james.ribbit;

import android.app.ActionBar;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.Toast;

import com.parse.ParseUser;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;


public class MyActivity extends Activity implements ActionBar.TabListener {
    public static final String TAG = MyActivity.class.getSimpleName();
    public static final int TakePhotoRequest = 0;
    public static final int TakeVideoRequest = 1;
    public static final int GetPhotoRequest = 2;
    public static final int GetVideoRequest = 3;
    public static final int MediaTypeImage= 4;
    public static final int MediaTypeVideo= 5;
    public static final int FILE_SIZE_LIMIT = 1024*1024*10 ; // 10 mb

    protected Uri mMediaUri;
    /**
     * The {@link /android.support.v4.view.(without /)"PagerAdapter(without the ")} that will provide
     * fragments for each of the sections. We use a
     * {@link "FragmentPagerAdapter(without the ")} derivative, which will keep every
     * loaded fragment in memory. If this becomes too memory intensive, it
     * may be best to switch to a
     * {@link /android.support.v13.app.(without /)"FragmentStatePagerAdapter(without the ")}.
     */
    SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@link "ViewPager(without the ")} that will host the section contents.
     */
    ViewPager mViewPager;
    protected DialogInterface.OnClickListener mDialogListener = new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialogInterface, int which) {
            switch (which) {
                case 0: // Take pic
                    Intent TakePhotoIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                    mMediaUri = getOutputMediaFileUri(MediaTypeImage);
                    if (mMediaUri==null) {
                        //display some sort of error
                        Toast.makeText(MyActivity.this,R.string.error_storage_external,Toast.LENGTH_LONG).show();
                    }
                    else {
                        TakePhotoIntent.putExtra(MediaStore.EXTRA_OUTPUT, mMediaUri);
                        startActivityForResult(TakePhotoIntent, TakePhotoRequest);
                    }

                    break;
                case 1: // Take vid
                    Intent videoIntent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);
                    mMediaUri = getOutputMediaFileUri(MediaTypeVideo);
                    if (mMediaUri==null) {
                        //display some sort of error
                        Toast.makeText(MyActivity.this,R.string.error_storage_external,Toast.LENGTH_LONG).show();
                    }
                    else {
                        videoIntent.putExtra(MediaStore.EXTRA_OUTPUT,mMediaUri);
                        videoIntent.putExtra(MediaStore.EXTRA_DURATION_LIMIT,10);
                        videoIntent.putExtra(MediaStore.EXTRA_VIDEO_QUALITY,0); // 0 = low res, 1 = high res
                        startActivityForResult(videoIntent,TakeVideoRequest);
                    }
                    break;
                case 2: // Choose pic
                    Intent ChoosePhotoIntent = new Intent(Intent.ACTION_GET_CONTENT);
                    ChoosePhotoIntent.setType("image/*");
                    startActivityForResult(ChoosePhotoIntent,GetPhotoRequest);
                    break;
                case 3: // Choose vid
                    Intent ChooseVideoIntent = new Intent(Intent.ACTION_GET_CONTENT);
                    ChooseVideoIntent.setType("video/*");
                    Toast.makeText(MyActivity.this,getString(R.string.video_warning) ,Toast.LENGTH_LONG).show();
                    startActivityForResult(ChooseVideoIntent, GetPhotoRequest);


                    break;
            }
        }


    };

    private Uri getOutputMediaFileUri(int mediaType) {

        if (isExternalStorageAvailible()) {
            //get uri
            //1  DIR
            String appName = MyActivity.this.getString(R.string.app_name);
            File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),appName);
            //2 create subDIR
            if (! mediaStorageDir.exists()) {
                if (mediaStorageDir.mkdirs()) {
                    Log.e(TAG,"FAILED IN CREATING DIR");
                    return null;
                }
            }

            //3 create filename

            //4 create file
            File mediaFile;
            Date now = new Date();
            String time = new SimpleDateFormat("MMddyyyy_HHmmss", Locale.getDefault()).format(now);
            String path = mediaStorageDir.getPath() + File.separator;
            if (mediaType == MediaTypeImage ) {
                mediaFile = new File(path+"IMAGE_"+time+".jpg");
            }
            else if (mediaType == MediaTypeVideo) {
                mediaFile = new File(path+"VIDEO_"+time +".mp4");
            }
            else {
                return null;
            }
            Log.d(TAG,"File " + Uri.fromFile(mediaFile));
            //5 return file

            return Uri.fromFile(mediaFile);
        }
        else {
            return null;
        }

    }
    private boolean isExternalStorageAvailible() {
        String state = Environment.getExternalStorageState();
        if (state.equals(Environment.MEDIA_MOUNTED)) {
            return true;
        }
        else { return false;}
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_my);
        ParseUser currentUser = ParseUser.getCurrentUser();
        if (currentUser == null) {

            navigateToLogin();
        } else {
            Log.i(TAG,currentUser.getUsername());
        }
        // Set up the action bar.
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(this,getFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        // When swiping between different sections, select the corresponding
        // tab. We can also use ActionBar.Tab#select() to do this if we have
        // a reference to the Tab.
        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                actionBar.setSelectedNavigationItem(position);
            }
        });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter. Also specify this Activity object, which implements
            // the TabListener interface, as the callback (listener) for when
            // this tab is selected.
            actionBar.addTab(
                    actionBar.newTab()
                            .setText(mSectionsPagerAdapter.getPageTitle(i))
                            .setTabListener(this));
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (resultCode == RESULT_OK) {
            //Add to gallery

            if (requestCode == GetPhotoRequest || requestCode == GetVideoRequest) {
                if (data == null) {
                    Toast.makeText(this, getString(R.string.general_error),Toast.LENGTH_LONG);
                } else {
                    mMediaUri = data.getData();
                    Log.i(TAG,"Media URI:" + mMediaUri);
                }
                if (requestCode == GetVideoRequest) {
                    // make sure vid is less than 10 mb
                    int filesize = 0;
                    InputStream inputStream = null;
                    try {
                        inputStream = getContentResolver().openInputStream(mMediaUri);
                        filesize = inputStream.available();
                    }
                    catch (FileNotFoundException e) {
                        Toast.makeText(this,getString(R.string.error_file),Toast.LENGTH_LONG).show();
                        return;
                    }
                    catch (IOException e) {
                        Toast.makeText(this,getString(R.string.error_file),Toast.LENGTH_LONG).show();
                        return;
                    }
                    finally {
                        try {
                            inputStream.close();
                        }
                        catch (IOException e){/* BLANK/!!!! */}
                    }
                    if (filesize >= FILE_SIZE_LIMIT) {
                        Toast.makeText(this,"this file is too large. Please select a different file.",Toast.LENGTH_LONG).show();
                        return;
                    }

                }
            } else {
                Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
                mediaScanIntent.setData(mMediaUri);
                sendBroadcast(mediaScanIntent);
            }

            Intent recipientsIntent = new Intent(this,RecipientsActivity.class);
            recipientsIntent.setData(mMediaUri);
            String fileType;
            if (requestCode == TakePhotoRequest || requestCode == GetPhotoRequest) {
                fileType = ParseConstants.TYPE_IMAGE;

            } else {
                fileType = ParseConstants.TYPE_VIDEO;
            }

            recipientsIntent.putExtra(ParseConstants.KEY_FILE_TYPE,fileType);
            startActivity(recipientsIntent);

        }
        else if (resultCode != RESULT_CANCELED) {
            Toast.makeText(this,getString(R.string.general_error),Toast.LENGTH_LONG).show();
        }

    }

    private void navigateToLogin() {
        Intent intent = new Intent(this, loginActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(intent);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        switch(id){
            case R.id.action_logout:
                ParseUser.logOut();
                navigateToLogin();
            case R.id.action_edit_friends:
                Intent intent = new Intent(this,EditFriendsActivity.class);
                startActivity(intent);
            case R.id.action_camera:
                AlertDialog.Builder builder = new AlertDialog.Builder(this);
                builder.setItems(R.array.camera_choices,mDialogListener);
                builder.show();
        }


        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
        // When the given tab is selected, switch to the corresponding page in
        // the ViewPager.
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    }



    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";




        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_inbox, container, false);
            return rootView;
        }
    }

}