SearchView from ArrayList

1/  activity_main.xml

<androidx.appcompat.widget.SearchView
    android:id="@+id/searchViewId"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:queryHint="Search items"
    android:background="#0df16e"/>

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerViewId"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginTop="8dp"
    android:padding="10dp"/>

2/ MyAddapter.java

private ArrayList<String> itemList;
    private ArrayList<String> itemListFull;

    public MyAdapter(ArrayList<String> itemList) {
        this.itemList = itemList;
        itemListFull = new ArrayList<>(itemList);
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(android.R.layout.simple_list_item_1, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        String item = itemList.get(position);
        holder.textView.setText(item);
    }

    @Override
    public int getItemCount() {
        return itemList.size();
    }


    public void filter(String text) {
        itemList.clear();
        if (text.isEmpty()) {
            itemList.addAll(itemListFull);
        } else {
            text = text.toLowerCase();
            for (String item : itemListFull) {
                if (item.toLowerCase().contains(text)) {
                    itemList.add(item);
                }
            }
        }
        notifyDataSetChanged();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public TextView textView;

        public ViewHolder(View view) {
            super(view);
            textView = view.findViewById(android.R.id.text1);
        }
    }
}

3/  MainActivity.Java.

 private MyAdapter adapter;
    private ArrayList<String> items;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        RecyclerView recyclerView = findViewById(R.id.recyclerViewId);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));


        items = new ArrayList<>();
        items.add("Argentina");
        items.add("Qatar");
        items.add("Kuwait");
        items.add("Korea");
        items.add("Kuwait");
        items.add("Afghanistan");
        items.add("Japan");
        items.add("Finland");
        items.add("Ethiopia");
        items.add("Romania");
        items.add("Portugal");
        items.add("Philippines");
        items.add("Paraguay");
        items.add("Panama");
        items.add("Palau");
        items.add("New Zealand");
        items.add("Bangladesh");



        adapter = new MyAdapter(items);
        recyclerView.setAdapter(adapter);


        androidx.appcompat.widget.SearchView searchView = findViewById(R.id.searchViewId);
        searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
            @Override
            public boolean onQueryTextSubmit(String query) {
                adapter.filter(query);
                return false;
            }

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

1/  Create A New Project .

1/  Create A New Project .