saved state with fragments

Expandable RecyclerView

Custom RecyclerViewAdapters for expanding and collapsing groups with support for multiple view types

Download

ExpandableRecyclerView:

compile 'com.thoughtbot:expandablerecyclerview:1.4'

ExpandableCheckRecyclerView:

compile 'com.thoughtbot:expandablecheckrecyclerview:1.4'

Usage

Let's say you are a rock star 🎸 and you want to build an app to show a list of your favorite Genres with a list of their top Artists.

First, define your custom ExpandableGroup class:

public class Genre extends ExpandableGroup<Artist> {

  public Genre(String title, List<Artist> items) {
    super(title, items);
  }
}

Next up, let's create the ChildViewHolder and GroupViewHolder. These are both wrappers around regular ol' RecyclerView.ViewHolders so implement any view inflation and binding methods you may need.

public class GenreViewHolder extends GroupViewHolder {

  private TextView genreTitle;

  public GenreViewHolder(View itemView) {
    super(itemView);
    genreTitle = itemView.findViewById(R.id.genre_title);
  }

  public void setGenreTitle(ExpandableGroup group) {
    genreTitle.setText(group.getTitle());
  }
}

public class ArtistViewHolder extends ChildViewHolder {

  private TextView artistName;

  public ArtistViewHolder(View itemView) {
    super(itemView);
    artistName = itemView.findViewById(R.id.artist_name);
  }

  public void setArtistName(Artist artist) {
    artistName.setText(artist.getTitle());
  }
}

Now we are ready for the juicy part - let's make our ExpandableRecyclerViewAdapter

By including your GroupViewHolder and ChildViewHolder in the definition of the class, you'll see that the onCreateGroupViewHolder and onCreateChildViewHolder methods return the correct type 👍

public class GenreAdapter extends ExpandableRecyclerViewAdapter<GenreViewHolder, ArtistViewHolder> {

  public GenreAdapter(List<? extends ExpandableGroup> groups) {
    super(groups);
  }

  @Override
  public GenreViewHolder onCreateGroupViewHolder(ViewGroup parent, int viewType) {
    View view = inflater.inflate(R.layout.list_item_genre, parent, false);
    return new GenreViewHolder(view);
  }

  @Override
  public ArtistViewHolder onCreateChildViewHolder(ViewGroup parent, int viewType) {
    View view = inflater.inflate(R.layout.list_item_artist, parent, false);
    return new ArtistViewHolder(view);
  }

  @Override
  public void onBindChildViewHolder(ArtistViewHolder holder, int flatPosition, ExpandableGroup group, int childIndex) {
    final Artist artist = ((Genre) group).getItems().get(childIndex);
    holder.setArtistName(artist.getName());
  }

  @Override
  public void onBindGroupViewHolder(GenreViewHolder holder, int flatPosition, ExpandableGroup group) {
    holder.setGenreTitle(group);
  }
}

Lastly you'll need either an Activity or Fragment to host your adapter. Once you've got that up and running, all that's left is to instantiate your fancy new GenreAdapter with a List<Genre>

public class GenreActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {

    ...

    List<Genre> genres = getGenres(); //see sample project's GenreDataFactory.java class for getGenres() method
    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    LinearLayoutManager layoutManager = new LinearLayoutManager(this);

    //instantiate your adapter with the list of genres
    GenreAdapter adapter = new GenreAdapter(genres);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setAdapter(adapter);

    ...

  }
}

Saving And Restoring Expand / Collapse State

If you want to save the expand and collapse state of your adapter, you have to explicitly call through to the adapters onSaveInstanceState() and onRestoreInstanceState()in the calling Activity

public class GenreActivity extends Activity {

  ...

  @Override
  protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    adapter.onSaveInstanceState(outState);
  }

  @Override
  protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    adapter.onRestoreInstanceState(savedInstanceState);
  }
}

Programmatic Expanding and Collapsing

The ExpandableRecyclerViewAdapter exposes methods to control the expanded and collapsed state.

First up we have the toggles, .toggleGroup(int) and .toggleGroup(ExpandableGroup). These are handy for when you control the states explicitly.

public class GenreActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {

    ...

    Button showAllToggle = findViewById(R.id.show_all);
    showAllToggle.setOnClickListener(new View.OnClickListener() {
      public void onClick(View v) {
        for (int i = adapter.groups().size() - 1; i >= 0; i--) {
          adapter.toggleGroup(i);
        }
      }
    });

  }
}

We also expose explicit methods to control the expanding and collapsing of specific groups, .expandGroup() and .collapseGroup(). For example, to expand the first group immediately:

public class GenreActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {

    ...

    adapter.expandGroup(0);

  }
}

Adding Custom Expand / Collapse Animations

If you want to add a custom Drawable that animates based on a groups state, override the expand() and collapse() methods in your GroupViewHolder:

public class GenreViewHolder extends GroupViewHolder {

  ...

  @Override
  public void expand() {
    animateExpand();
  }

  @Override
  public void collapse() {
    animateCollapse();
  }
}

Listening to Expand/Collapse events

If you want register an ExpandCollapseListener outside of the adapter, you can simply call setOnGroupExpandCollapseListener on the ExpandableRecyclerViewAdapter

  adapter.setOnGroupExpandCollapseListener(new GroupExpandCollapseListener() {
    @Override
    public void onGroupExpanded(ExpandableGroup group) {

    }

    @Override
    public void onGroupCollapsed(ExpandableGroup group) {

    }
  });

Multiple Child and Group Types

The MultiTypeExpandableRecyclerViewAdapter allows subclasses to implement multiple different view types for both children and groups.

Continuing with our genre example, let's say you wanted to display regular artists differently from your favorite artists. Let's start by making a new FavoriteArtistViewHolder

public class FavoriteArtistViewHolder extends ChildViewHolder {

  private TextView favoriteArtistName;

  public FavoriteArtistViewHolder(View itemView) {
    super(itemView);
    favoriteArtistName = (TextView) itemView.findViewById(R.id.list_item_favorite_artist_name);
  }

  public void setArtistName(String name) {
    favoriteArtistName.setText(name);
  }

Just like the regular ArtistViewHolder, FavoriteArtistViewHolder must extends ChildViewHolder.

Next up, let's create a subclass of MultiTypeExpandableRecyclerViewAdapter called MultiTypeGenreAdapter and let's add two static ints representing our two artist view types:

public class MultiTypeGenreAdapter extends MultiTypeExpandableRecyclerViewAdapter<GenreViewHolder, ChildViewHolder> {


  public static final int FAVORITE_VIEW_TYPE = 3;
  public static final int ARTIST_VIEW_TYPE = 4;
  ...

Notice we started used values > 2. That's because ExpandableListPosition.CHILD and ExpandableListPositon.GROUP are 1 and 2 respectively so they are already taken.

Since we only want a single view type for groups, we only need to override getChildViewType(). As getGroupViewType() will default to ExpandableListPosition.GROUP.

  @Override
  public int getChildViewType(int position, ExpandableGroup group, int childIndex) {
    if (((Genre) group).getItems().get(childIndex).isFavorite()) {
      return FAVORITE_VIEW_TYPE;
    } else {
      return ARTIST_VIEW_TYPE;
    }
  }

Since we provided custom view types for our children, we must also override isChild()

  @Override
  public boolean isChild(int viewType) {
    return viewType == FAVORITE_VIEW_TYPE || viewType == ARTIST_VIEW_TYPE;
  }

And now, just like in any other RecyclerView.Adapter in our onCreateChildViewHolder and our onBindChildViewHolder we can use the provided parameters to switch on the different view tyeps:

  @Override
  public ChildViewHolder onCreateChildViewHolder(ViewGroup parent, int viewType) {
    switch (viewType) {
      case ARTIST_VIEW_TYPE:
        View artist = from(parent.getContext()).inflate(R.layout.list_item_artist, parent, false);
        return new ArtistViewHolder(artist);
      case FAVORITE_VIEW_TYPE:
        View favorite =
            from(parent.getContext()).inflate(R.layout.list_item_favorite_artist, parent, false);
        return new FavoriteArtistViewHolder(favorite);
      default:
        throw new IllegalArgumentException("Invalid viewType");
    }
  }

  @Override
  public void onBindChildViewHolder(ChildViewHolder holder, int flatPosition, ExpandableGroup group,
      int childIndex) {
    int viewType = getItemViewType(flatPosition);
    Artist artist = ((Genre) group).getItems().get(childIndex);
    switch (viewType) {
      case ARTIST_VIEW_TYPE:
        ((ArtistViewHolder) holder).setArtistName(artist.getName());
        break;
      case FAVORITE_VIEW_TYPE:
        ((FavoriteArtistViewHolder) holder).setArtistName(artist.getName());
    }
  }

Expandable Check RecyclerView

An extension of expandablerecyclerview for checking single or multiple children within a group

The setup for the single and multi check versions is very similar to the expandablerecyclerview we walked through above. Here are a few of the notable differences...

CheckedExpandableGroup

Instead of ExpandableGroup you must use CheckedExpandableGroup. CheckedExpandableGroup is a subclass of ExpandableGroup that uses a SparseBooleanArray to hold onto which of it's children are checked.

The expandablecheckrecyclerview library comes with two default implementations - SingleCheckExpandableGroup and MultiCheckExpandableGroup.

Clearing Choices

The CheckableChildRecyclerViewAdapter has a clearChoices() which un checks any currently checked children.

CheckableChildViewHolder

The CheckableChildViewHolder is a subclass of ChildViewHolder that has a Checkable widget. The Checkable interface is initially not set, so in order to see your children view states update, you must set a View that implements Checkable in your view holder.

public class SingleCheckArtistViewHolder extends CheckableChildViewHolder {

  private CheckedTextView artistName;

  public SingleCheckArtistViewHolder(View itemView) {
    super(itemView);
    artistName = (CheckedTextView) itemView.findViewById(R.id.list_item_singlecheck_artist_name);
  }

  @Override
  public Checkable getCheckable() {
    return artistName;
  }
  ...
}

Listening to Child Click Events

There is a custom callback for click events on children of a CheckedExpandableGroup which returns you the View of the row item that was clicked, the current checked state of the child, the containing CheckedExpandableGroup group and the index of the child that was clicked.

  adapter.setChildClickListener(new OnCheckChildClickListener() {
    @Override
    public void onCheckChildCLick(View v, boolean checked, CheckedExpandableGroup group,
        int childIndex) {
    }
  });

Sample App

To see the complete code for all the above examples along with unit tests for the adapters check out the sample app. The app has the following packages:

expand

An example of basic ExpandableRecyclerViewAdapter

multicheck

An example of a CheckableChildRecyclerViewAdapter using MultiCheckExpandableGroup

single check

An example of a CheckableChildRecyclerViewAdapter using SingleCheckExpandableGroup

multi type

An example of a MultiTypeExpandableRecyclerViewAdapter using two different child view holders

Contributing

See the CONTRIBUTING document. Thank you, contributors!

License

About

Expandable RecyclerView is maintained by @mandybess

Expandable RecyclerView is maintained and funded by thoughtbot, inc. The names and logos for thoughtbot are trademarks of thoughtbot, inc.

We love open source software! See our other projects or hire us to help build your product.

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