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..

Possible duplicate of [How to implement onBackPressed() in Fragments?](http://stackoverflow.com/questions/5448653/how-to-implement-onbackpressed-in-fragments) — Code-Apprentice, Aug 22 '16 at 17:32

score 90 · Accepted Answer · edited Oct 30 '17 at 04:38

90

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).

edited Oct 30 '17 at 04:38

Sufian Latif

13,086
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answered Jan 16 '13 at 16:09

K Roobroeck

1,378
2
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3

replace() == remove(thisFragment).add(anotherFragment).. Replace is equal to both the methods in this order. – Zar E Ahmer Jun 27 '14 at 11:33
@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. – ToolmakerSteve Oct 24 '16 at 12:42

score 4 · Answer 2 · answered Jan 16 '13 at 09:24

4

Just remove first and the call super.onBackPressed

public void onBackPressed(){

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

}

answered Jan 16 '13 at 09:24

Pratik

30,639
18
84
159

score 0 · Answer 3 · edited Mar 12 '14 at 06:42

//lets wait for systems back to finish

 super.onBackPressed();

//here we believe a fragment was popped, so we need to remove the fragment from ourbackstack
if(fragmentBackStack.size()>0)
{
    Log.d("custombackstack","before back: "+fragmentBackStack.size()+" current:"+fragmentBackStack.peek());

    fragmentBackStack.pop();            
}
//after popping is the size > 0, if so we set current fragment from the top of stack, otherwise we default to home fragment.
if(fragmentBackStack.size()>0)
{           
    Log.d("custombackstack","after back: "+fragmentBackStack.peek());
currentFragment = fragmentBackStack.peek();         
}
else
{           
    //back stack empty
    currentFragment = HOME_FRAGMENT;
}

Android: Fragments backStack

3 Answers3

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