overriding back button in fragment

Question

I have an activity with different fragments in the tab selection, I want to override the back button so that it calls a method in the fragment that update the listview to the parent folder list. For now I've made this in the main activity:

    @Override
        public void onBackPressed()
        {
            ActionBar actionbar = getActionBar();
            if(actionbar.getSelectedTab().getPosition() == 0)
            {
                if(!fla.onBackPressed())
                    super.onBackPressed();
            }
        }

And this in the fragment:

   public boolean onBackPressed()
    {
        if(back_str.equals(MAIN_POINT)){
            Log.v("A", "BACK FIRST" + back_str);
            return false;
            }
        else
        {
            Log.v("A", "BACK PREMUTO");
            updateListViewFolder(back_str);
            return true;  //torna indietro nella view
        }
    }

back_str is a global string in the class referring to the current parent directory in the listview and it's updated every time I open a folder.

Seems that when I press the back button back_str is always = null

can someone help me and tell me a way I can solve this?

EDIT:

I'll try to explain me better, I've a listview inside the fragment that I use to navigate into the folder of the phone, starting from /storage/ when I press a folder it opens updating the listview calling this method:

public void updateListViewFolder(String newPath)
{
    ArrayList<Song> songsListTMP = new SongManager().getPlayList(newPath); //aggiungo tutte le canzoni
    songsListData.removeAll(songsListData);

    //AGGIUNGO LA CARTELLA PRECEDENTE
    File here = new File(newPath);
    back_str = here.getParent();
    Log.v("A", "S:"+back_str);
    Song back = new Song(back_str, true); //Sono directory
    songsListData.add(back);

    for(int i = 0; i < songsListTMP.size(); i++)
    {
        Song song = songsListTMP.get(i);
        songsListData.add(song); //tengo un attimo separate
    }

        for(File dir : here.listFiles() )
        {
            if(dir.isDirectory() && dir.canRead()){
                Song sdir = new Song(dir.getPath(), true); //Sono directory
                songsListData.add(sdir);
            }
        }

    getListView().invalidateViews();

    }

Now I want to return to the parent folder if the back button is selected, but somehow I get errors when I try to call the method onBackPressed of the fragment from the activity. I'm using a static variable string_str to store inside my fragment the path of the parent folder I want to update the list with, but somehow I can't get the list updated with the same updateListViewFolder method

Answer 1

Ok I've found the error. I wasn't calling the method of the instance of the fragment in the actionbar tab, I was just calling the method of that class. I made my class MyTabListener to set a tag to my fragment so that I could access to it with (FolderListActivity) getFragmentManager().findFragmentByTag("F1");

Here the class:

class MyTabListener implements ActionBar.TabListener {
    private Fragment mFragment;

    public MyTabListener(Fragment fragment) {
        mFragment = fragment;
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        if(mFragment instanceof FolderListActivity)
            ft.add(mFragment, "F1"); //mi occupo di settare un tag per recuperare la specifica istanza del fragment
        else
            ft.add(mFragment, "F0");
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        FolderListActivity f1 = (FolderListActivity) getFragmentManager().findFragmentByTag("F1"); //accedo allo specifico fragment
        if(f1 != null)
            f1.cleanView();
        ft.remove(mFragment);
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // do nothing
    }
}