Android: Fragments backStack

Question

Im trying to load an new fragment when a method is called. This method creates a new fragment and "replaces" the other fragment:

private void showTestFragment(Fragment oldFragment, boolean addBackStack, BaseAdapter adapter, int position) {
    Cursor cursor = (Cursor)adapter.getItem(position);
    if(cursor != null){

        int idx = cursor.getColumnIndexOrThrow(Episode._ID);
        long rowId = cursor.getLong(idx);

        FragmentManager fragmentManager = getFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

        if(oldFragment != null){
            Log.i(TAG, "Removing the old fragment");
            fragmentTransaction.remove(oldFragment);
        }

        TestFragment testFragment =  new TestFragment();
        testFragment.setId(rowId);

        fragmentTransaction.add(android.R.id.content, testFragment);

        if(addBackStack){
            Log.i(TAG, "Added to the backstack");
            fragmentTransaction.addToBackStack(TAG);
        }

        fragmentTransaction.commit();
        Fragment f = getFragmentManager()
                .findFragmentById(R.id.index);
        Log.i(TAG, "after commit, frag is "+ f);
    }
}

This works fine, until i go back. The last fragment, should be removed when i go back. Before i'm going to implement methods on the activities

public void onBackPressed(){}

to remove the last fragment, i want to know if i handle the fragment change correctly. It looks like i'm missing something here..

Solution 1

If you really want to replace the fragment then use replace() methode instead of doing a remove() and an add().

    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(..............);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit(); 

Don't forget to do the addToBackStack(null) so your previous state will be added to the backstack allowing you to go back with the back button.

See also https://developer.android.com/reference/android/app/FragmentTransaction.html#replace(int, android.app.Fragment, java.lang.String) .

Another good source is http://developer.android.com/guide/components/fragments.html (search for replace() function).

Solution 2

Just remove first and the call super.onBackPressed

public void onBackPressed(){

    // here remove code for your last fragment
    super.onBackPressed();

}

Comments

[Zar E Ahmer]

replace() == remove(thisFragment).add(anotherFragment).. Replace is equal to both the methods in this order.

[ToolmakerSteve]

@Nepster, true, but not always convenient. FWIW, The difference is that Replace removes ANY fragment(s) in the container; don't need to know thisFragment. One scenario where this matters is if Fragment A links to Fragment B1 which is replaced by Fragment B2. THEN if want "Back" button to go back to Fragment A (instead of to B1), we have to code that manually, because Android's back will [incorrectly IMHO] do "remove B1, add A" - the opposite of the original link from A to B1. B2 lurks in viewbehind. Our code has to know that B2 is the current fragment, not B1. Sometimes that is inconvenient.