Divide elements on groups in RecyclerView

For example you can:

1. Use a TreeMap<Date,List<Event>> for splitting elements by date. This will be a collection for keeping your business objects. Of course if you already have a similar structure you can keep it. It’s just important to have something for easily building list of items for populating UI with right elements order.

2. Define a dedicated abstract type for List items (e.g. ListItem) to wrap your business objects. Its implementation could be something like this:

   public abstract class ListItem {
   
       public static final int TYPE_HEADER = 0;
       public static final int TYPE_EVENT = 1;
   
       abstract public int getType();
   } 
   

3. Define a class for each of your List element type (here I added just two types but you can use many as you need):

   public class HeaderItem extends ListItem {
   
       private Date date;
   
       // here getters and setters 
       // for title and so on, built
       // using date
   
       @Override
       public int getType() {
           return TYPE_HEADER;
       }
   
   }
   
   public class EventItem extends ListItem {
   
       private Event event;
   
       // here getters and setters 
       // for title and so on, built 
       // using event
   
       @Override
       public int getType() {
           return TYPE_EVENT;
       }
   
   }
   

4. Create a List as follows (where mEventsMap is map build at point 1):

   List<ListItem> mItems;
   // ...
   mItems = new ArrayList<>();
   for (Date date : mEventsMap.keySet()) {
       HeaderItem header = new HeaderItem();
       header.setDate(date); 
       mItems.add(header);
       for (Event event : mEventsMap.get(date)) {
           EventItem item = new EventItem();
           item.setEvent(event);
           mItems.add(item);
       }
   }
   

5. Define an adapter for your RecyclerView, working on List defined at point 4. Here what is important is to override getItemViewType method as follows:

   @Override
   public int getItemViewType(int position) {
       return mItems.get(position).getType();
   }
   

   Then you need to have two layouts and ViewHolder for header and event items. Adapter methods should take care of this accordingly:

   @Override
   public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
       if (viewType == ListItem.TYPE_HEADER) {
           View itemView = mLayoutInflater.inflate(R.layout.view_list_item_header, parent, false);
           return new HeaderViewHolder(itemView);
       } else {
           View itemView = mLayoutInflater.inflate(R.layout.view_list_item_event, parent, false);
           return new EventViewHolder(itemView);
       }
   }
   
   
   @Override
   public void onBindViewHolder(final RecyclerView.ViewHolder viewHolder, final int position) {
       int type = getItemViewType(position);
       if (type == ListItem.TYPE_HEADER) {
           HeaderItem header = (HeaderItem) mItems.get(position);
           HeaderViewHolder holder = (HeaderViewHolder) viewHolder;
           // your logic here
       } else {            
           EventItem event = (EventItem) mItems.get(position);
           EventViewHolder holder = (EventViewHolder) viewHolder;
           // your logic here
       }
   }
   

Here it is a repository on GitHub providing an implementation of the approach explained above.