Hot switch to a viewpager page when a recyclerview item is clicked?

Question

I want to know how to switch to the current item of viewpager when a recyclerview item clicked

when clicking on a recyclerview item it will return the position of the clicked item easily. a toast message confirms this.

but when I use mViewPager.setCurrentItem(position); it returns null , I can confirm that viewpager has been initialized successfully because it is working well in onCreate of my activity.

here is the adapter of the recyclerview

    // ViewHolder adapter for RecyclerView
        public class PlanetViewHolder
                extends RecyclerView.ViewHolder
                implements View.OnClickListener {
            public PlanetViewHolder(View v) {
                super(v);
                v.setOnClickListener(this);
            }
    
            @Override
            public void onClick(View v) {
                int position = getPosition();
                mViewPager.setCurrentItem(position);    
                Toast.makeText(getContext(), "You have clicked " + ((TextView) v).getText(), Toast.LENGTH_SHORT).show();
    
    
            }
        }

here is the onCreate

public class TvShowEpisodeDetails extends MizActivity {

    private static final String SHOW_ID = "showId";

    private ArrayList<TvShowEpisode> mEpisodes = new ArrayList<TvShowEpisode>();
    private int mSeason, mEpisode;
    private String mShowId, mShowTitle;
    private ViewPager mViewPager;
    private DbAdapterTvShowEpisodes mDatabaseHelper;
    private Bus mBus;

    @Override
    protected int getLayoutResource() {
        return R.layout.viewpager_with_toolbar_overlay;
    }
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        mBus = MizuuApplication.getBus();
        super.onCreate(savedInstanceState);

        // Set theme
        setTheme(R.style.Mizuu_Theme_NoBackground);

        ViewUtils.setupWindowFlagsForStatusbarOverlay(getWindow(), true);

        ViewUtils.setProperToolbarSize(this, mToolbar);

        mShowId = getIntent().getExtras().getString(SHOW_ID);
        mSeason = getIntent().getExtras().getInt("season");
        mEpisode = getIntent().getExtras().getInt("episode");

        mDatabaseHelper = MizuuApplication.getTvEpisodeDbAdapter();

        Cursor cursor = mDatabaseHelper.getEpisodes(mShowId);
        try {
            while (cursor.moveToNext()) {
                mEpisodes.add(new TvShowEpisode(this, mShowId,
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE_TITLE)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE_PLOT)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_SEASON)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE_AIRDATE)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE_DIRECTOR)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE_WRITER)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE_GUESTSTARS)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_EPISODE_RATING)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_HAS_WATCHED)),
                        cursor.getString(cursor.getColumnIndex(DbAdapterTvShowEpisodes.KEY_FAVOURITE))
                        ));
            }
        } catch (Exception e) {
        } finally {
            cursor.close();
        }

        mShowTitle = MizuuApplication.getTvDbAdapter().getShowTitle(mShowId);
        setTitle(mShowTitle);

        mViewPager = (ViewPager) findViewById(R.id.awesomepager);
        mViewPager.setAdapter(new TvShowEpisodeDetailsAdapter(getSupportFragmentManager()));
        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                ViewUtils.updateToolbarBackground(TvShowEpisodeDetails.this, mToolbar, 0, mEpisodes.get(position).getTitle(), Color.TRANSPARENT);
            }
        });

        if (savedInstanceState != null) {
            mViewPager.setCurrentItem(savedInstanceState.getInt("tab", 0));
        } else {
            for (int i = 0; i < mEpisodes.size(); i++) {
                if (mEpisodes.get(i).getSeason().equals(MizLib.addIndexZero(mSeason)) && mEpisodes.get(i).getEpisode().equals(MizLib.addIndexZero(mEpisode))) {
                    mViewPager.setCurrentItem(i);
                    break;
                }
            }
        }
    }


    // ViewHolder adapter for RecyclerView
    public class PlanetViewHolder
            extends RecyclerView.ViewHolder
            implements View.OnClickListener {
        public PlanetViewHolder(View v) {
            super(v);
            v.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            int position = getPosition();
            mViewPager.setCurrentItem(position);

            //mViewPager.setAdapter(new TvShowEpisodeDetailsAdapter(getSupportFragmentManager()));
            //mViewPager.setCurrentItem(position);
            //Toast.makeText(getContext(), "You have clicked " + ((TextView) v).getText(), Toast.LENGTH_SHORT).show();


        }
    }
rest of the code
}

Answer 1

Based on your stacktraces, I can conclude that the way you handle UI elements are in the wrong order, meaning lifecycle is ignored.

You should NOT invoke UI elements in your activity from your viewHolder, as viewHolders are "part" of Recyercycleview which is not aware of the activity lifecycle.

A common pattern to invoke UI elements in your activity from your viewHolder is:

            Listener
Activity <-----------> RecyclerView_Adapter

Well, since you have a listener already, your have a good start.

Just move your mViewPager.setCurrentItem(position); from viewHolder to inside the overriden onClick Method in Activity through the listener you have.

Let me know if you have more questions, you are almost there!

EDIT

If your viewpager is in a fragment, then you should add mViewPager.setCurrentItem(position); to the overriden onClick Method in fragment. Simply means that you should invoke mViewPager.setCurrentItem(position); directly from your fragment and use the Adapter Listener just to get the correct time to invoke mViewPager.setCurrentItem(position);.

What is an Adapter Listener in Android?