MainActivity.java

package nisrulz.github.example.autocompletetextview;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
  List<String> li;
  AutoCompleteTextView auto;

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

    li=new ArrayList<String>();
    li.add("Item 1");
    li.add("Item 2");
    li.add("Item 3");

    auto=(AutoCompleteTextView) findViewById(R.id.autoCompleteTextView1);
    final EditText et1=(EditText) findViewById(R.id.editText1);
    Button b1=(Button) findViewById(R.id.button1);

    add();

    b1.setOnClickListener(new View.OnClickListener() {

      @Override
      public void onClick(View v) {
        // TODO Auto-generated method stub

        li.add(et1.getText().toString());
        et1.setText(null);

        add();

        Toast.makeText(getBaseContext(), "Item Added",
            Toast.LENGTH_SHORT).show();
      }
    });
  }

  private void add() {
    // TODO Auto-generated method stub

    ArrayAdapter<String> adp=new ArrayAdapter<String>(this,
        android.R.layout.simple_dropdown_item_1line,li);

    auto.setThreshold(1);
    auto.setAdapter(adp);
  }
}