This was asked some time ago now, but based on the answer that @nacho_zona3 provided, and previous experience with fragments, the issue is that the views have not been created by the time you are trying to find them with the findViewById() method in onCreate() to fix this, move the following code:

// 1. get a reference to recyclerView
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.list);

// 2. set layoutManger
recyclerView.setLayoutManager(new LinearLayoutManager(this));

// this is data from recycler view
ItemData itemsData[] = { new ItemData("Indigo",R.drawable.circle),
        new ItemData("Red",R.drawable.color_ic_launcher),
        new ItemData("Blue",R.drawable.indigo),
        new ItemData("Green",R.drawable.circle),
        new ItemData("Amber",R.drawable.color_ic_launcher),
        new ItemData("Deep Orange",R.drawable.indigo)};


// 3. create an adapter
MyAdapter mAdapter = new MyAdapter(itemsData);
// 4. set adapter
recyclerView.setAdapter(mAdapter);
// 5. set item animator to DefaultAnimator
recyclerView.setItemAnimator(new DefaultItemAnimator()); 

to your fragment's onCreateView() call. A small amount of refactoring is required because all variables and methods called from this method have to be static. The final code should look like:

 public class ColorsFragment extends Fragment {

     public ColorsFragment() {}

     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
         Bundle savedInstanceState) {

         View rootView = inflater.inflate(R.layout.fragment_colors, container, false);
         // 1. get a reference to recyclerView
         RecyclerView recyclerView = (RecyclerView) rootView.findViewById(R.id.list);

         // 2. set layoutManger
         recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

         // this is data from recycler view
         ItemData itemsData[] = {
             new ItemData("Indigo", R.drawable.circle),
                 new ItemData("Red", R.drawable.color_ic_launcher),
                 new ItemData("Blue", R.drawable.indigo),
                 new ItemData("Green", R.drawable.circle),
                 new ItemData("Amber", R.drawable.color_ic_launcher),
                 new ItemData("Deep Orange", R.drawable.indigo)
         };


         // 3. create an adapter
         MyAdapter mAdapter = new MyAdapter(itemsData);
         // 4. set adapter
         recyclerView.setAdapter(mAdapter);
         // 5. set item animator to DefaultAnimator
         recyclerView.setItemAnimator(new DefaultItemAnimator());

         return rootView;
     }
 }

So the main thing here is that anywhere you call findViewById() you will need to use rootView.findViewById()


You should retrieve RecyclerView in a Fragment after inflating core View using that View. Perhaps it can't find your recycler because it's not part of Activity

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
    final View view = inflater.inflate(R.layout.fragment_artist_tracks, container, false);
    final FragmentActivity c = getActivity();
    final RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
    LinearLayoutManager layoutManager = new LinearLayoutManager(c);
    recyclerView.setLayoutManager(layoutManager);

    new Thread(new Runnable() {
        @Override
        public void run() {
            final RecyclerAdapter adapter = new RecyclerAdapter(c);
            c.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    recyclerView.setAdapter(adapter);
                }
            });
        }
    }).start();

    return view;
}