Tutorial

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Check the minimal expand & collapse sample code on GitHub.

Tutorial

Step 1. Extend AbstractExpandableItemAdapter instead of RecyclerView.Adapter

First, you need to extend AbstractExpandableItemAdapter to use expandable items feature. This class implements RecyclerView.Adapter's methods and some of them are sealed via final keyword. Instead, it provides some Group / Child prefixed version of RecyclerView.Adapter methods.

class MyChildItem {
    public long id;
}

class MyGroupItem {
    public long id;
    List<MyChildItem> children;
}

class MyAdapter extends AbstractExpandableItemAdapter<MyAdapter.MyGroupVH, MyAdapter.MyChildVH> {
    List<MyGroupItem> items;

    public MyAdapter() {
        setHasStableIds(true); // this is required for expandable feature.
    }

    @Override
    public int getGroupCount() { ... }

    @Override
    public int getChildCount(int groupPosition) { ... }

    @Override
    public long getGroupId(int groupPosition) { ... }

    @Override
    public long getChildId(int groupPosition, int childPosition) { ... }

    @Override
    public MyGroupVH onCreateGroupViewHolder(ViewGroup parent, int viewType) { ... }

    @Override
    public MyChildViewHolder onCreateChildViewHolder(ViewGroup parent, int viewType) { ... }

    @Override
    public void onBindGroupViewHolder(MyGroupVH holder, int groupPosition, int viewType) { ... }

    @Override
    public void onBindChildViewHolder(MyChildViewHolder holder, int groupPosition, int childPosition, int viewType) { ... }

    @Override
    public boolean onCheckCanExpandOrCollapseGroup(MyGroupVH holder, int groupPosition, int x, int y, boolean expand) { ... }
}

Step 2. Implement each method of AbstractExpandableItemAdapter

Step 3. Implement getGroupCount() / getChildCount()

The corresponding RecyclerView.Adapter's method is getItemCount().

@Override
public int getGroupCount() {
    return items.size();
}

@Override
public int getChildCount(int groupPosition) {
    reuturn items.get(groupPosition).size();
}

Step 4. Implement getGroupId() / getChildId()

The corresponding RecyclerView.Adapter's method is getItemId().

@Override
public int getGroupId(int groupPosition) {
    return items.get(groupPosition).id;
}

@Override
public int getChildId(int groupPosition, int childPosition) {
    reuturn items.get(groupPosition).children.get(childPosition).id;
}

Step 5. Implement onCreateGroupViewHolder() / onCreateChildViewHolder()

The corresponding RecyclerView.Adapter's method is onCreateViewHolder().

@Override
public MyGroupVH onCreateGroupViewHolder(ViewGroup parent, int viewType) {
    View v = LayoutInfrater.from(parent.getContext()).inflate(R.layout.item_group, parent, false);
    return new MyGroupVH(v);
}

@Override
public MyChildViewHolder onCreateChildViewHolder(ViewGroup parent, int viewType) {
    View v = LayoutInfrater.from(parent.getContext()).inflate(R.layout.item_child, parent, false);
    return new MyChildVH(v);
}

Step 6. Implement onBindGroupViewHolder() / onBindChildViewHolder()

The corresponding RecyclerView.Adapter's method is onBindViewHolder().

@Override
public void onBindGroupViewHolder(MyGroupVH holder, int groupPosition, int viewType) {
    MyGroupItem item = items.get(groupPosition);
    holder.text.setText(...);
}

@Override
public void onBindChildViewHolder(MyChildViewHolder holder, int groupPosition, int childPosition, int viewType) {
    MyChildItem item = items.get(groupPosition).children.get(childPosition);
    holder.text.setText(...);
}

Step 7. Implement onCheckCanExpandOrCollapseGroup()

Just returns true for make group items automatically respond to click events.

@Override
public boolean onCheckCanExpandOrCollapseGroup(MyGroupViewHolder holder, int groupPosition, int x, int y, boolean expand) {
    return true;
}

[Tip] If you want to handle expand/colappse action manually

Make this method reutrns false. Then call RecyclerViewExpandableItemManager.expandGroup() / collapseGroup() on click item events.

» Sample code: AddRemoveExpandableExampleAdapter#handleOnClickGroupItemContainerView()

» Related issue: Force expand/colapse #11

Step 8. Custom more and details of the implementation

Please refer to the demo app implementation for more details.