Expandable

Usage

Add the dependency.

dependencies {
    implementation 'com.github.Omega-R:OmegaRecyclerView:1.9.5@aar' // AndroidX
}

Adding OmegaExpandableRecyclerView to layout:

<com.omega_r.libs.omegarecyclerview.expandable_recycler_view.OmegaExpandableRecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:childAnimation="Dropdown"
        app:expandMode="single"/>

Create adapter like following:

public class ExpandableAdapter extends OmegaExpandableRecyclerView.Adapter<QuoteGlobalInfo, Quote> {

    @Override
    protected ExGroupViewHolder provideGroupViewHolder(@NonNull ViewGroup viewGroup) {
        return new ExGroupViewHolder(viewGroup);
    }

    @Override
    protected ExChildViewHolder provideChildViewHolder(@NonNull ViewGroup viewGroup) {
        return new ExChildViewHolder(viewGroup);
    }

    class ExGroupViewHolder extends GroupViewHolder {

        private TextView textView;

        ExGroupViewHolder(ViewGroup parent) {
            super(parent, R.layout.item_exp_group);
            textView = findViewById(R.id.textview_group_name);
        }

        @Override
        protected void onExpand(GroupViewHolder viewHolder, int groupIndex) {
            // nothing
        }

        @Override
        protected void onCollapse(GroupViewHolder viewHolder, int groupIndex) {
            // nothing
        }

        @Override
        protected void onBind(QuoteGlobalInfo item) {
            textView.setText(item.getTitle());
        }
    }

    class ExChildViewHolder extends ChildViewHolder {

        private TextView textView;

        ExChildViewHolder(ViewGroup parent) {
            super(parent, R.layout.item_exp_child);
            textView = findViewById(R.id.textview_child_content);
        }

        @Override
        protected void onBind(Quote item) {
            textView.setText(item.getQuote());
        }
    }
}

Use one of the following methods to set items for adapter or use adapter constructors:

public final void setItems(@NonNull List<ExpandableViewData<G, CH>> expandableViewData)
public final void setItems(ExpandableViewData<G, CH>... expandableViewData)
public final void setItemsAsGroupProviders(GroupProvider<G, CH>... groupProviders)
public final void setItemsAsGroupProviders(@NonNull List<GroupProvider<G, CH>> groupProviders)

Your view data (group and childs) should be wrapped with ExpandableViewData using one of the following ways:

ExpandableViewData(G group, List<CH> childs, @Nullable Integer stickyId) // constructor

static <G, CH> ExpandableViewData<G, CH> of(G group, @Nullable Integer stickyId, List<CH> childs)
static <G, CH> ExpandableViewData<G, CH> of(G group, @Nullable Integer stickyId, CH... childs)

Or it should implement interface

public interface GroupProvider<G, CH> {
    G provideGroup();

    List<CH> provideChilds();

    @Nullable
    Integer provideStickyId();
}

It is available to update only child item using

// Adapter
public void notifyChildChanged(CH child)

You can set expandMode and childAnimation both with xml attr and programmatically

Available expandModes are single and multiple

Available childAnimations are Dropdown and Fade

You can simply create your own animations by extending ExpandableItemAnimator class and then just set it to RecyclerView recyclerView.setItemAnimator

It is possible to emulate background expanding using "app:backgrounds" attribute.

Create LevelListDrawable in res/drawable folder

expandable_backgrounds.xml

<?xml version="1.0" encoding="utf-8"?>
<level-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:maxLevel="@integer/backgroundGroupCollapsed" android:drawable="@drawable/group_collapsed" />
    <item android:maxLevel="@integer/backgroundGroupExpanded" android:drawable="@drawable/group_expanded" />
    <item android:maxLevel="@integer/backgroundFirstChild" android:drawable="@drawable/child_bg" />
    <item android:maxLevel="@integer/backgroundLastChild" android:drawable="@drawable/child_last" />
    <item android:maxLevel="@integer/backgroundChild" android:drawable="@drawable/child_bg" />
</level-list>

And then just add app:backgrounds="@drawable/expandable_backgrounds" attribute to your OmegaExpandableRecyclerView

OmegaExpandableRecyclerView have 2 ways of using Sticky Header feature: Default (that is described above in StickyHeader section) and StickyGroups. Last one is the way to make GroupViewHolders work as StickyHeaders.

To do that just add app:stickyGroups="true" attribute to your OmegaExpandableRecyclerView and be sure that you set items providing unique stickyId for each group.

And, of course, you CAN use both sticky behaviors at the same time