Managing the back button with nested fragment

Question

I have a MainActivity with a content_container to load Fragments in it.

In one of the Fragment I also have a sub_container to load Fragments.

In the MainActivity i manage the back button with a stack of Fragment:

public Fragment addFragmentToStack(Fragment fragment){
    if(fragmentStack.size()>MAX_NUM_FRAGMENTS){
        fragmentStack.remove(0);
    }
    return fragmentStack.push(fragment);
}   

@Override
public void onBackPressed() {
    if (fragmentStack.size() > 0) {
        fragmentStack.pop();
        if (MyApplication.fragmentStack.size() > 0) {               
            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
            ft.replace(R.id.content_container, fragmentStack.peek());
            ft.commit();
        }
    }
}

and whenever I want to replace a Fragment in my content_container I use

Fragment someFragment = new SomeFragment(); 
fragmentTransaction.replace(R.id.content_container, ((MainActivity)getActivity()).addFragmentToStack(someFragment), "");
fragmentTransaction.commit();

One Fragment is a gallery, with a menu to load a photos or a videos Fragment in it (so the gallery is the parent Fragment and the photos and videos Fragments are children).

In order to be able to add the photo gallery and the video gallery in the stack, I use in the GalleryFragment:

if(mType.equals("photos")){
    Fragment videoFragment = new VideoFragment();
    fragmentTransaction.replace(R.id.sub_container, videoFragment, "");
    ((MainActivity)getActivity()).addFragmentToStack(this);
}
else{
    Fragment photoFragment = new PhotoFragment();
    fragmentTransaction.replace(R.id.sub_container, photoFragment, "");
    ((MainActivity)getActivity()).addFragmentToStack(this);
}

i.e. I add the parent GalleryFragment in the stack.

When I go from the videos to the photos gallery, for instance, and press the back Button, the code in MainActivity's onBackPressed is executed, and the current GalleryFragment instance is replaced by the instance in the stack, but its sub_container is empty (none of onCreateView or onResume is called).

Anybody can help?

score 0 · Answer 1 · answered Apr 29 '13 at 21:01

0

Ok, adding the same instance to the stack was not a good idea. Instead, if I add a new instance, it works perfectly, i.e. :

instead of

((MainActivity)getActivity()).addFragmentToStack(this);

use

GalleryFragment fragment = new GalleryFragment();
Bundle bundle = new Bundle();
bundle.putString("type", "photos"); // or bundle.putString("type", "videos");
                                    // in order to know what to load once in there
fragment.setArguments(bundle);
((MainActivity)getActivity()).addFragmentToStack(fragment);

answered Apr 29 '13 at 21:01

jul

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This approach is problematic. Never instantiate Fragments with the constructor and don't keep references to it. The system can destroy your fragment at any time, this is why you should always use the FragmentManager method `getFragmentByTag`. – wkarl Feb 10 '15 at 09:54
@DrJerkberg: "Never instantiate Fragments with the constructor". Why? – jul Feb 12 '15 at 08:33

Managing the back button with nested fragment

1 Answers1