Add custom filter to RecyclerView

One of the most requested enhancements for the Random Contact App is for a way to filter contacts with the custom contact picker that is used in it. Since it seemed like a good reusable component, I added the module named MultiContactPicker along with the rearchitecture of my Andorid library project lib-aeApps.

Lets see how to add a filter for a RecyclerView in an Android app.

As you should have guessed, when we apply a filter we would show a subset of the data in the list. From the RecyclerView’s point of view, the list of data that it has to show has changed - a call to notifyDataSetChanged() is to be expected.

And where do we manage the data for a RecyclerView? The backing adapter which extends the class RecyclerView.Adapter.

The first step is for the adapter to implement the android.widget.Filterable class

  class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.ViewHolder>
     implements Filterable {
       ...
     }

Next, we create a copy of the source data. But use the filtered list to render the view.

  private final List<ContactInfo> contactInfoList;
  private List<ContactInfo> filteredContacts;

 MyRecyclerViewAdapter(final List<ContactInfo> values) {
     filteredContacts = new ArrayList<>(values);
     contactInfoList = values;
 }

When we implementing the Filterable class, we need to add a method called getFilter(). This is where the actual filtering occurs. The performFiltering() method is passed in a search string, and we need to filter the list data based on this. The filtering criteria is upto your specific use case. I have added some optimizations so that our friend notifyDataSetChanged() is only called when required. And ofcourse when the search string is empty, we copy back the original list.

 @Override
 public Filter getFilter() {
     return new Filter() {
         @Override
         protected FilterResults performFiltering(CharSequence charSequence) {
             boolean dataUpdated = false;
             if (charSequence.length() == 0) {
                 if (filteredContacts.size() < contactInfoList.size()) {
                     filteredContacts = new ArrayList<>(contactInfoList);
                     dataUpdated = true;
                 }
             } else {
                 filteredContacts = filterContactsByName(charSequence.toString().toLowerCase());
                 dataUpdated = true;
             }

             FilterResults filterResults = new FilterResults();
             filterResults.values = dataUpdated;
             return filterResults;
         }

         @Override
         protected void publishResults(CharSequence charSequence, FilterResults filterResults) {
             boolean dataUpdated = Boolean.parseBoolean(filterResults.values.toString());
             if (dataUpdated) {
                 notifyDataSetChanged();
             }
         }
     };
 }

Next step is to add a SearchView to the layout which includes the RecyclerView.

 <androidx.appcompat.widget.SearchView
     android:id="@+id/multiContactSearchView"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     app:iconifiedByDefault="false"
     app:queryHint="@string/str_multi_contact_search_hint" />

And finally in the parent activity or Fragment, we respond to the QueryText of the SearchView. Whenever there is a change in text, we simply invoke the filter() method on the adapter.

  searchView = findViewById(R.id.multiContactSearchView);
  searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
   @Override
   public boolean onQueryTextSubmit(String query) {
       return false;
   }

   @Override
   public boolean onQueryTextChange(String newText) {
       adapter.getFilter().filter(newText);
       return false;
   }
  });

These are all the changes that are required. Pretty much all of the above code except the implementation for filterContactsByName() is generic and can be re-used for any project. Please reach out to me for any doubts. See the references to the source code hosted on GitHub.

References