Android：片段堆栈的问题

Question

I've created a Video app with a master/detail fragment navigation. This app has a single activity.

From the list fragment you click a record icon to navigate to the Camera Preview to record video.

Lets say my ListFragment is [1], my camera preview fragment is [2] and my detail fragment is [3]. Right now my navigation is [1] - [2] - [3].

Now when the user is 3 and presses the back button, I believe the app is trying to naviagate back to [2] and the app crashes. I want to the app to always navigate back to [1] when the user presses the back button.

I have played around with different combinations of addToBackStack and nothing seems to be working. Please help if you can!

All this code is from the main activity:

When first entering the app (opens the [1]):

VideoListFragment videoListFragment = new VideoListFragment();

            videoListFragment.setArguments(getIntent().getExtras());

            getFragmentManager().beginTransaction()
                    .add(R.id.container, videoListFragment)
                    .commit();

When navigating to [2]:

CameraFragment cameraFragment = new CameraFragment();
        getFragmentManager().beginTransaction()
                .replace(R.id.container, cameraFragment)
                .commit();

When navigating to [3]:

VideoDetailFragment videoDetailFragment = new VideoDetailFragment();
        Bundle args = new Bundle();
        args.putString(VideoDetailFragment.UUID, String.valueOf(uuid));
        videoDetailFragment.setArguments(args);
        getFragmentManager().beginTransaction()
                .replace(R.id.container, videoDetailFragment, "VideoDetailFragment")
                .addToBackStack(null)
                .commit();

Update: Ok I've got the navigation working by overriding the back button before with this method in the main activity:

 @Override
    public void onBackPressed() {
        if (getFragmentManager().findFragmentByTag("VideoDetailFragment") != null) {
            // I'm viewing VideoDetailFragment
            getFragmentManager().beginTransaction()
                    .replace(R.id.container, new VideoListFragment())
                    .addToBackStack(null)
                    .commit();
        } else {
            super.onBackPressed();
        }
    }

but now once I'm back in the ListFragment when I press the back button it does nothing? I can't get out of the app?

Answer 1

You said you tried different combinations, but it seems to me like you should call addToBackStack when navigating to [2] and not to [3].

In response to your update - You can customize the back button by checking

int depth = getFragmentManager().getBackStackEntryCount();
if (depth == 0)
    // exit app
else
    // switch fragments

EDIT: Noticed you are using the FragmentManager directly and not the support fragment manager