How can I implement a Material Design Expand/Collapse List on Android?

Question

I am looking to implement a material list of this style. How can I do this on Android? What classes should I look at? Are there any existing libraries that could make implementi

Answer 1

I implemented such a list using this library:
expandable-recycler-view

There is a related blog, but it refers to an old version:
Expand a RecyclerView in Four Steps

It's basically an adapter where you can supply a list of parent elements that contain the children. You further have to specify two holders for the parents and the children. See the library's page for more details.

class MyChild {
  // add data
}
class MyParentListItem implements ParentListItem {
  private final List mChildren;

  MyParentListItem(List children) {
    mChildren = children;
    // add other data
  }

  @Override
  public List getChildItemList() {
    return mChildren;
  }

  @Override
  public boolean isInitiallyExpanded() {
    return false;
  }
}

class MyParentViewHolder extends ParentViewHolder {
  MyParentViewHolder(View itemView) {
    super(itemView);
    // get other views with itemView.findViewById(..);
  }
}

class MyChildViewHolder extends ChildViewHolder {
  MyParentViewHolder(View itemView) {
    super(itemView);
    // get other views with itemView.findViewById(..);
  }
}

public class MyExpandableAdapter extends ExpandableRecyclerAdapter {
  private final LayoutInflater mInflater;
  public MyExpandableAdapter(List parentItemList, Context context) {
    super(parentItemList);
    mInflater = LayoutInflater.from(context);
  }

  @Override
  public MyParentViewHolder onCreateParentViewHolder(ViewGroup parentViewGroup) {
    final View itemView = mInflater.inflate(R.layout.parent_layout, parentViewGroup, false);
    return new MyParentViewHolder(itemView);
  }

  @Override
  public MyChildViewHolder onCreateChildViewHolder(ViewGroup childViewGroup) {
    final View itemView = mInflater.inflate(R.layout.child_layout, childViewGroup, false);
    return new MyChildViewHolder(itemView);
  }

  // bind data to holders in the onBind methods
}