Removing a Fragment from the back stack

问题:

I have a 3 fragments in an activity when the a tablet is held in portrait. However I only have 2 of these fragments when in landscape. The problem I am having is when going from portrait to landscape the activity is creating the 3rd fragment. I receive and error as this fragment cannot be created.

I have worked out that this fragment is being created because it is in the back stack.

I have tried to remove the fragment in the onDestroy method by using

FragmentTransaction f = fragmentManager.beginTransaction();
f.remove(mf);
f.commit();

However the I get an error saying that I cannot use this function after the onSaveInstanceState

What would be the correct way of taking this fragment out of the back stack?

Update

I should probably add that the fragment I am having problems with is a mapFragment from this libary

https://github.com/petedoyle/android-support-v4-googlemaps

The way I use it is like so

mf = MapFragment.newInstance(1, true);

ft = fragmentManager.beginTransaction();
ft.replace(R.id.mapContainer, mf);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack("map");
ft.commit();

回答1:

You add to the back state from the FragmentTransaction and remove from the backstack using FragmentManager pop methods:

FragmentManager manager = getActivity().getSupportFragmentManager();
FragmentTransaction trans = manager.beginTransaction();
trans.remove(myFrag);
trans.commit();
manager.popBackStack();

回答2:

I created a code to jump to the desired back stack index, it worked fine to my purpose.

ie. I have Fragment1, Fragment2 and Fragment3, I want to jump from Fragment3 to Fragment1

I created a method called onBackPressed in Fragment3 that jumps to Fragment1

Fragment3:

public void onBackPressed() {
    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.popBackStack(fragmentManager.getBackStackEntryAt(fragmentManager.getBackStackEntryCount()-2).getId(), FragmentManager.POP_BACK_STACK_INCLUSIVE);
}

In the activity, I need to know if my current fragment is the Fragment3, so I call the onBackPressed of my fragment instead calling super

FragmentActivity:

@Override
public void onBackPressed() {
    Fragment f = getSupportFragmentManager().findFragmentById(R.id.my_fragment_container);
    if (f instanceof Fragment3)
    {
        ((Fragment3)f).onBackPressed();
    } else {
        super.onBackPressed();
    }
}

回答3:

What happens if the fragment that you want to remove is not on top of the stack?

Then you can use theses functions

popBackStack(int arg0, int arg1);

popBackStack(String arg0, int arg1);