توضیحات:

Free Expandable RecyclerView Demo app contains two fragments screen "BASIC" and "EXPANDABLE". As the name suggests In "BASIC", Normal RecyclerView used to show simple vertically scrollable List Items, As shown in screens timer will reduce every second (Like stopwatch).

In "EXPANDABLE", customized RecyclerView (i.e ExpandableRecyclerView) used to expanding and collapsing list items.

You can view the source code also