Update your MainActivity method:

@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); progress = findViewById(R.id.progress); recycler = findViewById(R.id.recycler); recycler.setHasFixedSize(true); recycler.setLayoutManager(new LinearLayoutManager(this)); adapter = new PostAdapter(this, new ArrayList()); recycler.setAdapter(adapter); fetchData(); } 

myApi.getData().subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(new Observer<List<Model>>() { @Override public void onSubscribe(Disposable d) { } @Override public void onNext(List<Model> models) { if(models.size() > 0){ progress.setVisibility(View.INVISIBLE); Log.d("count",String.valueOf(models.size())); adapter.setItems(models) } } @Override public void onError(Throwable e) { Toast.makeText(getApplicationContext(),e.getMessage(),Toast.LENGTH_SHORT).show(); } @Override public void onComplete() { } }); }