Custom RecyclerViewAdapters for expanding and collapsing groups with support for multiple view types
ExpandableRecyclerView:
implementation 'com.thoughtbot:expandablerecyclerview:1.3'ExpandableCheckRecyclerView:
implementation 'com.thoughtbot:expandablecheckrecyclerview:1.4'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 onBind(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 đź‘Ť
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 = ((Artist) group).getItems().get(childIndex);
holder.setArtistName(artist.getName());
}
@Override
public void onBindGroupViewHolder(GenreViewHolder holder, int flatPosition,
ExpandableGroup group) {
holder.setGenreTitle(group);
}
}Lastly let's you'll need either an Activity or Fragment to host your adapter. Once you've got that up and running, all that's left if 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();
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);
...
}
}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);
}
}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();
}
}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) {
}
});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());
}
}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...
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.
The CheckableChildRecyclerViewAdapter has a clearChoices() which un checks any currently checked children.
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;
}
...
}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) {
}
});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:
An example of basic ExpandableRecyclerViewAdapter
An example of a CheckableChildRecyclerViewAdapter using MultiCheckExpandableGroup
An example of a CheckableChildRecyclerViewAdapter using SingleCheckExpandableGroup
An example of a MultiTypeExpandableRecyclerViewAdapter using two different child view holders
See the CONTRIBUTING document. Thank you, contributors!
Expandable RecyclerView is Copyright (c) 2016 thoughtbot, inc. It is free software, and may be redistributed under the terms specified in the LICENSE file.
Expandable RecyclerView is maintained by @mandybess
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