Java tutorial
/* * Copyright 2015 Google Inc. All rights reserved. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.samples.apps.iosched.explore; import android.app.Activity; import android.app.Fragment; import android.content.Context; import android.content.Intent; import android.content.SharedPreferences; import android.net.Uri; import android.os.Bundle; import android.os.Parcelable; import android.preference.PreferenceManager; import android.support.annotation.NonNull; import android.support.v4.app.ActivityCompat; import android.support.v4.app.ActivityOptionsCompat; import android.support.v4.util.Pair; import android.support.v4.util.SparseArrayCompat; import android.support.v4.view.ViewCompat; import android.support.v7.widget.CardView; import android.support.v7.widget.RecyclerView; import android.text.TextUtils; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.Button; import android.widget.ImageView; import android.widget.TextView; import com.google.samples.apps.iosched.R; import com.google.samples.apps.iosched.archframework.ModelWithLoaderManager; import com.google.samples.apps.iosched.archframework.PresenterImpl; import com.google.samples.apps.iosched.archframework.UpdatableView; import com.google.samples.apps.iosched.explore.ExploreIOModel.ExploreIOQueryEnum; import com.google.samples.apps.iosched.explore.ExploreIOModel.ExploreIOUserActionEnum; import com.google.samples.apps.iosched.explore.data.EventData; import com.google.samples.apps.iosched.explore.data.ItemGroup; import com.google.samples.apps.iosched.explore.data.LiveStreamData; import com.google.samples.apps.iosched.explore.data.MessageData; import com.google.samples.apps.iosched.explore.data.SessionData; import com.google.samples.apps.iosched.injection.ModelProvider; import com.google.samples.apps.iosched.provider.ScheduleContract; import com.google.samples.apps.iosched.session.SessionDetailActivity; import com.google.samples.apps.iosched.settings.ConfMessageCardUtils; import com.google.samples.apps.iosched.settings.SettingsUtils; import com.google.samples.apps.iosched.ui.widget.DrawShadowFrameLayout; import com.google.samples.apps.iosched.ui.widget.recyclerview.ItemMarginDecoration; import com.google.samples.apps.iosched.ui.widget.recyclerview.UpdatableAdapter; import com.google.samples.apps.iosched.util.AccountUtils; import com.google.samples.apps.iosched.util.ImageLoader; import com.google.samples.apps.iosched.util.ThrottledContentObserver; import com.google.samples.apps.iosched.util.TimeUtils; import com.google.samples.apps.iosched.util.UIUtils; import java.util.ArrayList; import java.util.List; import static android.content.SharedPreferences.OnSharedPreferenceChangeListener; import static com.google.samples.apps.iosched.settings.ConfMessageCardUtils.ConferencePrefChangeListener; /** * Display the Explore I/O cards. There are three styles of cards, which are referred to as Groups * by the CollectionView implementation. * <p/> * <ul> <li>The live-streaming session cards.</li> <li>Time sensitive message cards.</li> <li>Session * topic cards.</li> </ul> * <p/> * Only the final group of cards is dynamically loaded from a {@link * android.content.ContentProvider}. */ public class ExploreIOFragment extends Fragment implements UpdatableView<ExploreIOModel, ExploreIOQueryEnum, ExploreIOUserActionEnum> { /** * Used to load images asynchronously on a background thread. */ private ImageLoader mImageLoader; /** * RecyclerView containing a stream of cards to display to the user. */ private RecyclerView mCardList = null; /** * Adapter for providing data for the stream of cards. */ private ExploreAdapter mAdapter; /** * Empty view displayed when {@code mCardList} is empty. */ private View mEmptyView; private List<UserActionListener> mListeners = new ArrayList<>(); private ThrottledContentObserver mSessionsObserver, mTagsObserver; private ConferencePrefChangeListener mConfMessagesAnswerChangeListener = new ConferencePrefChangeListener() { @Override protected void onPrefChanged(String key, boolean value) { fireReloadEvent(); } }; private OnSharedPreferenceChangeListener mSettingsChangeListener = new OnSharedPreferenceChangeListener() { @Override public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) { if (SettingsUtils.PREF_DECLINED_WIFI_SETUP.equals(key)) { fireReloadEvent(); } else if (AccountUtils.PREF_ACTIVE_ACCOUNT.equals(key)) { fireReloadEvent(); } } }; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { final View root = inflater.inflate(R.layout.explore_io_frag, container, false); mCardList = (RecyclerView) root.findViewById(R.id.explore_card_list); mCardList.setHasFixedSize(true); final int cardVerticalMargin = getResources().getDimensionPixelSize(R.dimen.spacing_normal); mCardList.addItemDecoration(new ItemMarginDecoration(0, cardVerticalMargin, 0, cardVerticalMargin)); mEmptyView = root.findViewById(android.R.id.empty); return root; } @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); mImageLoader = new ImageLoader(getActivity(), R.drawable.io_logo); initPresenter(); } @Override public void displayData(final ExploreIOModel model, final ExploreIOQueryEnum query) { // Only display data when the tag metadata is available. if (model.getTagMetadata() != null) { if (mAdapter == null) { mAdapter = new ExploreAdapter(getActivity(), model, mImageLoader); mCardList.setAdapter(mAdapter); } else { mAdapter.update(model); } mEmptyView.setVisibility(mAdapter.getItemCount() > 0 ? View.GONE : View.VISIBLE); } } @Override public void displayErrorMessage(final ExploreIOQueryEnum query) { // No UI changes when error with query } @Override public void displayUserActionResult(final ExploreIOModel model, final ExploreIOUserActionEnum userAction, final boolean success) { switch (userAction) { case RELOAD: displayData(model, ExploreIOQueryEnum.SESSIONS); break; } } @Override public Uri getDataUri(final ExploreIOQueryEnum query) { switch (query) { case SESSIONS: return ScheduleContract.Sessions.CONTENT_URI; default: return Uri.EMPTY; } } @Override public Context getContext() { return getActivity(); } @Override public void addListener(UserActionListener toAdd) { mListeners.add(toAdd); } private void initPresenter() { ExploreIOModel model = ModelProvider.provideExploreIOModel(getDataUri(ExploreIOQueryEnum.SESSIONS), getContext(), getLoaderManager()); PresenterImpl presenter = new PresenterImpl(model, this, ExploreIOUserActionEnum.values(), ExploreIOQueryEnum.values()); presenter.loadInitialQueries(); } @Override public void onResume() { super.onResume(); getActivity().invalidateOptionsMenu(); final DrawShadowFrameLayout drawShadowFrameLayout = (DrawShadowFrameLayout) getActivity() .findViewById(R.id.main_content); if (drawShadowFrameLayout != null) { // configure fragment's top clearance to take our overlaid Toolbar into account. drawShadowFrameLayout.setShadowTopOffset(UIUtils.calculateActionBarSize(getActivity())); } } @Override public void onAttach(Activity activity) { super.onAttach(activity); // Register preference change listeners ConfMessageCardUtils.registerPreferencesChangeListener(getContext(), mConfMessagesAnswerChangeListener); SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getContext()); sp.registerOnSharedPreferenceChangeListener(mSettingsChangeListener); // Register content observers mSessionsObserver = new ThrottledContentObserver(new ThrottledContentObserver.Callbacks() { @Override public void onThrottledContentObserverFired() { fireReloadEvent(); fireReloadTagsEvent(); } }); mTagsObserver = new ThrottledContentObserver(new ThrottledContentObserver.Callbacks() { @Override public void onThrottledContentObserverFired() { fireReloadTagsEvent(); } }); } @Override public void onDetach() { super.onDetach(); if (mConfMessagesAnswerChangeListener != null) { ConfMessageCardUtils.unregisterPreferencesChangeListener(getContext(), mConfMessagesAnswerChangeListener); } if (mSettingsChangeListener != null) { SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getContext()); sp.unregisterOnSharedPreferenceChangeListener(mSettingsChangeListener); } getActivity().getContentResolver().unregisterContentObserver(mSessionsObserver); getActivity().getContentResolver().unregisterContentObserver(mTagsObserver); } /** * Let all UserActionListener know that the video list has been reloaded and that therefore we * need to update the display of sessions. */ private void fireReloadEvent() { if (!isAdded()) { return; } for (UserActionListener h1 : mListeners) { Bundle args = new Bundle(); args.putInt(ModelWithLoaderManager.KEY_RUN_QUERY_ID, ExploreIOModel.ExploreIOQueryEnum.SESSIONS.getId()); h1.onUserAction(ExploreIOModel.ExploreIOUserActionEnum.RELOAD, args); } } private void fireReloadTagsEvent() { if (!isAdded()) { return; } for (UserActionListener h1 : mListeners) { Bundle args = new Bundle(); args.putInt(ModelWithLoaderManager.KEY_RUN_QUERY_ID, ExploreIOModel.ExploreIOQueryEnum.TAGS.getId()); h1.onUserAction(ExploreIOModel.ExploreIOUserActionEnum.RELOAD, args); } } /** * Adapter for providing cards (Messages, Keynote, Live Stream and conference Tracks) * for the Explore fragment. */ private static class ExploreAdapter extends UpdatableAdapter<ExploreIOModel, RecyclerView.ViewHolder> { private static final int TYPE_TRACK = 0; private static final int TYPE_MESSAGE = 1; private static final int TYPE_KEYNOTE = 2; private static final int TYPE_LIVE_STREAM = 3; private static final int TYPE_EVENT_DATA = 4; private static final int LIVE_STREAM_TRACK_ID = R.string.live_now; private static final int EVENT_DATA_TRACK_ID = 999; // Immutable state private final Activity mHost; private final LayoutInflater mInflater; private final ImageLoader mImageLoader; private final RecyclerView.RecycledViewPool mRecycledViewPool; // State private List mItems; // Maps of state keyed on track id private SparseArrayCompat<UpdatableAdapter> mTrackSessionsAdapters; private SparseArrayCompat<Parcelable> mTrackSessionsState; ExploreAdapter(@NonNull Activity activity, @NonNull ExploreIOModel model, @NonNull ImageLoader imageLoader) { mHost = activity; mImageLoader = imageLoader; mInflater = LayoutInflater.from(activity); mRecycledViewPool = new RecyclerView.RecycledViewPool(); mItems = processModel(model); setupSessionAdapters(model); } public void update(@NonNull ExploreIOModel model) { // Attempt to update our data in-place so as not to lose scroll position etc. final List newItems = processModel(model); boolean changed = false; if (newItems.size() != mItems.size()) { changed = true; } else { for (int i = 0; i < newItems.size(); i++) { final Object newCard = newItems.get(i); final Object oldCard = mItems.get(i); if (newCard.equals(oldCard)) { if (newCard instanceof ItemGroup) { final ItemGroup newTrack = (ItemGroup) newCard; mTrackSessionsAdapters.get(getTrackId(newTrack)).update(newTrack.getSessions()); } } else { changed = true; break; } } } if (changed) { // Couldn't update existing model, do a full refresh mItems = newItems; setupSessionAdapters(model); notifyDataSetChanged(); } } @Override public int getItemViewType(final int position) { final Object item = mItems.get(position); if (item instanceof LiveStreamData) { return TYPE_LIVE_STREAM; } else if (item instanceof ItemGroup) { return TYPE_TRACK; } else if (item instanceof MessageData) { return TYPE_MESSAGE; } else if (item instanceof SessionData) { return TYPE_KEYNOTE; } else if (item instanceof EventData) { return TYPE_EVENT_DATA; } throw new IllegalArgumentException("Unknown view type."); } @Override public RecyclerView.ViewHolder onCreateViewHolder(final ViewGroup parent, final int viewType) { switch (viewType) { case TYPE_EVENT_DATA: return createEventViewHolder(parent); case TYPE_TRACK: return createTrackViewHolder(parent); case TYPE_MESSAGE: return createMessageViewHolder(parent); case TYPE_KEYNOTE: return createKeynoteViewHolder(parent); case TYPE_LIVE_STREAM: return createLiveStreamViewHolder(parent); default: throw new IllegalArgumentException("Unknown view type."); } } @Override public void onBindViewHolder(final RecyclerView.ViewHolder holder, final int position) { switch (getItemViewType(position)) { case TYPE_TRACK: bindTrack((TrackViewHolder) holder, (ItemGroup) mItems.get(position)); break; case TYPE_MESSAGE: bindMessage((MessageViewHolder) holder, (MessageData) mItems.get(position)); break; case TYPE_KEYNOTE: bindKeynote((KeynoteViewHolder) holder, (SessionData) mItems.get(position)); break; case TYPE_LIVE_STREAM: bindLiveStream((TrackViewHolder) holder, (LiveStreamData) mItems.get(position)); break; case TYPE_EVENT_DATA: bindEventData((EventDataViewHolder) holder, (EventData) mItems.get(position)); break; } } private void bindEventData(final EventDataViewHolder holder, final EventData eventData) { int trackId = getTrackId(eventData); holder.cards.setAdapter(mTrackSessionsAdapters.get(trackId)); holder.cards.getLayoutManager().onRestoreInstanceState(mTrackSessionsState.get(trackId)); } @Override public void onViewRecycled(final RecyclerView.ViewHolder holder) { if (holder instanceof TrackViewHolder) { // Cache the scroll position of the session list so that we can restore it in onBind final TrackViewHolder trackHolder = (TrackViewHolder) holder; final int position = trackHolder.getAdapterPosition(); if (position != RecyclerView.NO_POSITION) { final int trackId = getTrackId((ItemGroup) mItems.get(position)); mTrackSessionsState.put(trackId, trackHolder.sessions.getLayoutManager().onSaveInstanceState()); } } super.onViewRecycled(holder); } @Override public int getItemCount() { return mItems.size(); } private @NonNull EventDataViewHolder createEventViewHolder(final ViewGroup parent) { final EventDataViewHolder holder = new EventDataViewHolder( mInflater.inflate(R.layout.explore_io_event_card, parent, false)); holder.cards.setHasFixedSize(true); holder.cards.setRecycledViewPool(mRecycledViewPool); ViewCompat.setImportantForAccessibility(holder.cards, ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_NO_HIDE_DESCENDANTS); holder.headerImage.setImageResource(R.drawable.explore_io_ontheground_header); holder.title.setText(R.string.explore_io_on_the_ground_title); return holder; } private @NonNull TrackViewHolder createTrackViewHolder(final ViewGroup parent) { final TrackViewHolder holder = new TrackViewHolder( mInflater.inflate(R.layout.explore_io_track_card, parent, false)); holder.sessions.setHasFixedSize(true); holder.sessions.setRecycledViewPool(mRecycledViewPool); ViewCompat.setImportantForAccessibility(holder.sessions, ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_NO_HIDE_DESCENDANTS); holder.header.setOnClickListener(new View.OnClickListener() { @Override public void onClick(final View v) { final int position = holder.getAdapterPosition(); if (position == RecyclerView.NO_POSITION) return; final ItemGroup track = (ItemGroup) mItems.get(position); final Intent intent = new Intent(mHost, ExploreSessionsActivity.class); intent.putExtra(ExploreSessionsActivity.EXTRA_FILTER_TAG, track.getId()); final ActivityOptionsCompat options = ActivityOptionsCompat.makeSceneTransitionAnimation(mHost, Pair.create((View) holder.headerImage, mHost.getString(R.string.transition_track_header)), Pair.create((View) holder.title, mHost.getString(R.string.transition_track_title)), Pair.create(holder.itemView, mHost.getString(R.string.transition_track_background))); ActivityCompat.startActivity(mHost, intent, options.toBundle()); } }); return holder; } private @NonNull MessageViewHolder createMessageViewHolder(final ViewGroup parent) { final MessageViewHolder holder = new MessageViewHolder( mInflater.inflate(R.layout.explore_io_message_card, parent, false)); // Work with pre-existing infrastructure which supplied a click listener and relied on // a shared pref listener & a reload to dismiss message cards. // By setting our own click listener and manually calling onClick we can remove the // item in the adapter directly. holder.buttonStart.setOnClickListener(new View.OnClickListener() { @Override public void onClick(final View v) { final int position = holder.getAdapterPosition(); if (position == RecyclerView.NO_POSITION) return; final MessageData message = (MessageData) mItems.get(position); message.getStartButtonClickListener().onClick(holder.buttonStart); mItems.remove(position); notifyItemRemoved(position); } }); holder.buttonEnd.setOnClickListener(new View.OnClickListener() { @Override public void onClick(final View v) { final int position = holder.getAdapterPosition(); if (position == RecyclerView.NO_POSITION) return; final MessageData message = (MessageData) mItems.get(position); message.getEndButtonClickListener().onClick(holder.buttonEnd); mItems.remove(position); notifyItemRemoved(position); } }); return holder; } private @NonNull KeynoteViewHolder createKeynoteViewHolder(final ViewGroup parent) { final KeynoteViewHolder holder = new KeynoteViewHolder( mInflater.inflate(R.layout.explore_io_keynote_card, parent, false)); holder.clickableItem.setOnClickListener(new View.OnClickListener() { @Override public void onClick(final View v) { final int position = holder.getAdapterPosition(); if (position == RecyclerView.NO_POSITION) return; final SessionData keynote = (SessionData) mItems.get(position); final Intent intent = new Intent(mHost, SessionDetailActivity.class); intent.setData(ScheduleContract.Sessions.buildSessionUri(keynote.getSessionId())); final ActivityOptionsCompat options = ActivityOptionsCompat.makeSceneTransitionAnimation(mHost, Pair.create(holder.itemView, mHost.getString(R.string.transition_session_background)), Pair.create((View) holder.thumbnail, mHost.getString(R.string.transition_session_image))); ActivityCompat.startActivity(mHost, intent, options.toBundle()); } }); return holder; } private @NonNull TrackViewHolder createLiveStreamViewHolder(final ViewGroup parent) { final TrackViewHolder holder = new TrackViewHolder( mInflater.inflate(R.layout.explore_io_track_card, parent, false)); ViewCompat.setImportantForAccessibility(holder.sessions, ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_NO_HIDE_DESCENDANTS); holder.header.setOnClickListener(new View.OnClickListener() { @Override public void onClick(final View v) { final Intent intent = new Intent(mHost, ExploreSessionsActivity.class); intent.setData( ScheduleContract.Sessions.buildSessionsAfterUri(TimeUtils.getCurrentTime(mHost))); intent.putExtra(ExploreSessionsActivity.EXTRA_SHOW_LIVE_STREAM_SESSIONS, true); ActivityCompat.startActivity(mHost, intent, null); } }); return holder; } private void bindTrack(final TrackViewHolder holder, final ItemGroup track) { bindTrackOrLiveStream(holder, track, track.getTitle()); } private void bindMessage(final MessageViewHolder holder, final MessageData message) { holder.description.setText(message.getMessageString(mHost)); if (message.getIconDrawableId() > 0) { holder.icon.setVisibility(View.VISIBLE); holder.icon.setImageResource(message.getIconDrawableId()); } else { holder.icon.setVisibility(View.GONE); } if (message.getStartButtonStringResourceId() != -1) { holder.buttonEnd.setVisibility(View.VISIBLE); holder.buttonStart.setText(message.getStartButtonStringResourceId()); } else { holder.buttonStart.setVisibility(View.GONE); } if (message.getEndButtonStringResourceId() != -1) { holder.buttonEnd.setVisibility(View.VISIBLE); holder.buttonEnd.setText(message.getEndButtonStringResourceId()); } else { holder.buttonEnd.setVisibility(View.GONE); } } private void bindKeynote(final KeynoteViewHolder holder, final SessionData keynote) { holder.title.setText(keynote.getSessionName()); if (!TextUtils.isEmpty(keynote.getImageUrl())) { mImageLoader.loadImage(keynote.getImageUrl(), holder.thumbnail); } if (!TextUtils.isEmpty(keynote.getDetails())) { holder.description.setText(keynote.getDetails()); } } private void bindLiveStream(final TrackViewHolder holder, final LiveStreamData data) { bindTrackOrLiveStream(holder, data, mHost.getString(R.string.live_now)); } private void bindTrackOrLiveStream(final TrackViewHolder holder, final ItemGroup track, final String title) { holder.title.setText(title); holder.header.setContentDescription(title); if (track.getPhotoUrl() != null) { holder.headerImage.setScaleType(ImageView.ScaleType.CENTER_CROP); mImageLoader.loadImage(track.getPhotoUrl(), holder.headerImage); } else { holder.headerImage.setScaleType(ImageView.ScaleType.FIT_CENTER); holder.headerImage.setImageResource(R.drawable.ic_hash_io_16_monochrome); } final int trackId = getTrackId(track); holder.sessions.setAdapter(mTrackSessionsAdapters.get(trackId)); holder.sessions.getLayoutManager().onRestoreInstanceState(mTrackSessionsState.get(trackId)); } /** * Process the given {@link ExploreIOModel} to create the list of items to be displayed by * the {@link RecyclerView}. */ private List processModel(final ExploreIOModel model) { final ArrayList exploreCards = new ArrayList(); // Add any Message cards final List<MessageData> messages = model.getMessages(); if (messages != null && !messages.isEmpty()) { exploreCards.addAll(messages); } // Add Keynote card. final SessionData keynote = model.getKeynoteData(); if (keynote != null) { exploreCards.add(keynote); } // Add Event Cards if onsite. if (SettingsUtils.isAttendeeAtVenue(mHost)) { final EventData eventData = model.getEventData(); if (eventData != null && !eventData.getCards().isEmpty()) { exploreCards.add(eventData); } } // Add Live Stream card. final LiveStreamData liveStream = model.getLiveStreamData(); if (liveStream != null && liveStream.getSessions().size() > 0) { exploreCards.add(liveStream); } // Add track cards, ordered alphabetically exploreCards.addAll(model.getOrderedTracks()); return exploreCards; } /** * Setup adapters for tracks which have child session lists */ private void setupSessionAdapters(final ExploreIOModel model) { final int trackCount = model.getOrderedTracks().size() + (model.getLiveStreamData() != null ? 1 : 0) + (model.getEventData() != null ? 1 : 0); mTrackSessionsAdapters = new SparseArrayCompat<>(trackCount); mTrackSessionsState = new SparseArrayCompat<>(trackCount); final LiveStreamData liveStream = model.getLiveStreamData(); if (liveStream != null && liveStream.getSessions().size() > 0) { mTrackSessionsAdapters.put(getTrackId(liveStream), new LiveStreamSessionsAdapter(mHost, liveStream.getSessions(), mImageLoader)); } final EventData eventData = model.getEventData(); if (eventData != null && eventData.getCards() != null && eventData.getCards().size() > 0) { mTrackSessionsAdapters.put(getTrackId(eventData), new EventDataAdapter(mHost, eventData.getCards())); } for (final ItemGroup group : model.getOrderedTracks()) { mTrackSessionsAdapters.put(getTrackId(group), SessionsAdapter.createHorizontal(mHost, group.getSessions())); } } /** * A derived ID for each track; used as a key for some state objects */ private int getTrackId(Object track) { if (track instanceof LiveStreamData) { return LIVE_STREAM_TRACK_ID; } else if (track instanceof EventData) { return EVENT_DATA_TRACK_ID; } else if (track instanceof ItemGroup) { return ((ItemGroup) track).getId().hashCode(); } return 0; } } private static class EventDataViewHolder extends RecyclerView.ViewHolder { final CardView card; final ViewGroup header; final ImageView headerImage; final TextView title; final RecyclerView cards; public EventDataViewHolder(View itemView) { super(itemView); card = (CardView) itemView; header = (ViewGroup) card.findViewById(R.id.header); headerImage = (ImageView) card.findViewById(R.id.header_image); title = (TextView) header.findViewById(R.id.title); cards = (RecyclerView) card.findViewById(R.id.cards); } } private static class TrackViewHolder extends RecyclerView.ViewHolder { final CardView card; final ViewGroup header; final ImageView headerImage; final TextView title; final RecyclerView sessions; public TrackViewHolder(View itemView) { super(itemView); card = (CardView) itemView; header = (ViewGroup) card.findViewById(R.id.header); headerImage = (ImageView) card.findViewById(R.id.header_image); title = (TextView) header.findViewById(R.id.title); sessions = (RecyclerView) card.findViewById(R.id.sessions); } } private static class MessageViewHolder extends RecyclerView.ViewHolder { final ImageView icon; final TextView description; final Button buttonStart; final Button buttonEnd; public MessageViewHolder(final View itemView) { super(itemView); icon = (ImageView) itemView.findViewById(R.id.icon); description = (TextView) itemView.findViewById(R.id.description); buttonStart = (Button) itemView.findViewById(R.id.buttonStart); buttonEnd = (Button) itemView.findViewById(R.id.buttonEnd); } } private static class KeynoteViewHolder extends RecyclerView.ViewHolder { final ImageView thumbnail; final TextView title; final TextView description; final ViewGroup clickableItem; public KeynoteViewHolder(final View itemView) { super(itemView); thumbnail = (ImageView) itemView.findViewById(R.id.thumbnail); title = (TextView) itemView.findViewById(R.id.title); description = (TextView) itemView.findViewById(R.id.description); clickableItem = (ViewGroup) itemView.findViewById(R.id.explore_io_clickable_item); } } }