How to pass Argument from MasterActivity to DetailActivity's NavigationDrawerFragment?

Question

TL;DR VERSION:

In Android master-detail pattern, how do I let the MasterActivity pass a value to the DetailFragment's parent activity (DetailActivity)? Because the DetailActivity is the file that stores the NavigationDrawerFragment.

Things I've considered:

• Callbacks (I don't know how that would work)
• Using getActivity() and calling functions on the parent activity to pass the argument. It seems less "clean" of a solution and highly coupled.

Is there a better way to do this?

---

LONG VERSION

I have a master-detail pattern, but the detail was changed so that the "up" button no longer goes back to the master list, but opens up a navigation drawer.

Right now, I have "dummy" code, so my navigation drawer has 3 items that all open the same page that was already there when you first clicked on the item in the Master list.

My main problem is: The master list can pass the SongDetailFragment.ARG_ITEM_ID argument to the detail, but the navigation drawer does not have access to the SongDetailFragment.ARG_ITEM_ID argument in the SongDetailFragment.java, because the navigation drawer is implemented in SongDetailActivity.java.

The master list passes in an argument to the detail fragment with the line detailIntent.putExtra(SongDetailFragment.ARG_ITEM_ID, id); :

SongListActivity.java

/**
 * Callback method from {@link SongListFragment.Callbacks}
 * indicating that the item with the given ID was selected.
 */
@Override
public void onItemSelected(String id) {
    if (mTwoPane) {
        // In two-pane mode, show the detail view in this activity by
        // adding or replacing the detail fragment using a
        // fragment transaction.
        Bundle arguments = new Bundle();
        arguments.putString(SongDetailFragment.ARG_ITEM_ID, id);
        SongDetailFragment fragment = new SongDetailFragment();
        fragment.setArguments(arguments);
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.songlist_detail_container, fragment)
                .commit();

    } else {
        // In single-pane mode, simply start the detail activity
        // for the selected item ID.
        Intent detailIntent = new Intent(this, SongDetailActivity.class);
        detailIntent.putExtra(SongDetailFragment.ARG_ITEM_ID, id); //<-------- Argument
        startActivity(detailIntent);
    }
}

But I can't pass that argument along when I click on one of the 3 dummy options in the navigation drawer, because the navigation drawer is in SongDetailActivity.java.

SongDetailActivity.java

//---------- NAVIGATION DRAWER -------------
    @Override
    public void onNavigationDrawerItemSelected(int position) {
        // update the main content by replacing fragments
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.songlist_detail_container, PlaceholderFragment.newInstance(position + 1))
                .commit();
    }

I tried copying and pasting this code from SongDetailFragment.java's onCreate method into SongDetailActivity.java's onCreate method, hoping that I could just access the same SongDetailFragment.ARG_ITEM_ID variable from SongDetailActivity, but it had compile errors such as Cannot resolve getArguments(). I later realized that the Master was only "putting an extra" in the Fragment, not the Activity.

SongDetailFragment.java

 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setHasOptionsMenu(true);
        if (getArguments().containsKey(ARG_ITEM_ID)) {
            // Load the dummy title specified by the fragment
            // arguments. In a real-world scenario, use a Loader
            // to load title from a title provider.
            mItem = SongItem.ITEM_MAP.get(getArguments().getString(ARG_ITEM_ID));
        }
    }

So, I need some way of letting the navigation drawer store the SongDetailFragment.ARG_ITEM_ID variable from the Master, so it can fetch the correct data from the model for each of its views. How can I do that?

---

Shared Preferences? I considered using shared preferences, but I think it's a bad idea because it will be hard to erase the data for all the use cases of leaving the "detail". I think I need something less global than that. Preferrably, if I can just get the Master to pass an argument to SongDetailActivity (and ultimately to the Navigation Drawer), that would be perfect!

---

Callbacks? I was looking over my code files to think of something, and I found this "callback" stuff that was generated with Android Studio's Master-Detail wizard. It sounds applicable when it says "This mechanism allows activities to be notified of item selections," but I'm not sure. Any insight or feedback on the applicability of callbacks is appreciated!

    /**
     * A callback interface that all activities containing this fragment must
     * implement. This mechanism allows activities to be notified of item
     * selections.
     */
    public interface Callbacks {
        /**
         * Callback for when an item has been selected.
         */
        public void onItemSelected(String id);
    }

    /**
     * A dummy implementation of the {@link Callbacks} interface that does
     * nothing. Used only when this fragment is not attached to an activity.
     */
    private static Callbacks sDummyCallbacks = new Callbacks() {
        @Override
        public void onItemSelected(String id) {

        }
    };

 @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        // Activities containing this fragment must implement its callbacks.
        if (!(activity instanceof Callbacks)) {
            throw new IllegalStateException("Activity must implement fragment's callbacks.");
        }

        mCallbacks = (Callbacks) activity;
    }

    @Override
    public void onDetach() {
        super.onDetach();

        // Reset the active callbacks interface to the dummy implementation.
        mCallbacks = sDummyCallbacks;
    }

    @Override
    public void onListItemClick(ListView listView, View view, int position, long id) {
        super.onListItemClick(listView, view, position, id);

        // Notify the active callbacks interface (the activity, if the
        // fragment is attached to one) that an item has been selected.
        mCallbacks.onItemSelected(SongItem.ITEMS.get(position).id);
    }

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getActivity() and Setter Method? I found this question Passing data between a fragment and its container activity . I will give it a try, but it seems strongly coupled and like a bad solution. It is just passing data directly to the parent activity via the fragment using a parent activity's method (such as a setter).

Answer 1

I mistakenly thought that the SongListActivity.java was only creating an intent for SongDetailFragment.java, but it was creating an intent for the SongDetailActivity.java. When I saw SongDetailFragment.ARG_ITEM_ID it confused me.

The code that I misunderstood:

Intent detailIntent = new Intent(this, SongDetailActivity.class);
        detailIntent.putExtra(SongDetailFragment.ARG_ITEM_ID, id); //<-------- Argument
        startActivity(detailIntent);

My solution:

I had to change a lot of things along the way to get this solution, and I can't remember everything I did, but this is the final result:

So, I actually just had to just go into the SongDetailActivity.java's onCreate method, and extract the bundled parameter like this:

mSongId = getIntent().getStringExtra(SongDetailFragment.ARG_ITEM_ID);

Then I had to just edit this in SongDetailActivity.java's onNavigationDrawerItemSelected method and have it actually instantiate the correct fragment, and pass along the mSongId in the bundle:

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    FragmentManager fragmentManager = getSupportFragmentManager();


   //------------ THE DEFAULT CODE THAT WASN'T PASSING THE DATA TO THE FRAGMENT----------
    if(position == 1) {
        fragmentManager.beginTransaction()
                .replace(R.id.songlist_detail_container, PlaceholderFragment.newInstance(position + 1, mSongId)) //<------ I actually do not want a placeholder fragment. I want my SongDetailFragment.
                .commit();
    }
    // ------------THE CODE I ADDED THAT WORKS-------------:
    else {
        SongDetailFragment sdf = new SongDetailFragment(); //<--------- Correct fragment class that I actually needed.
        Bundle args = new Bundle();
        args.putString(SongDetailFragment.ARG_ITEM_ID, mSongId); //<-------- PASS ALONG THE PARAMETER
        sdf.setArguments(args);
        fragmentManager.beginTransaction()
                .replace(R.id.songlist_detail_container,sdf)
                .commit();
    }
}

It works now! I hope this helps somebody.

Conclusion

To pass an argument from the master (SongListActivity.java) to the detail's navigation drawer (SongDetailActivity.java's NavigationDrawerFragment.java), I had to put it as an extra in the intent from the master to the detail, and modify the detail's navigation drawer callbacks to use the argument. I did not need to pass anything from the fragment to it's parent activity, like I thought.