<AutoCompleteTextView 
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:id="@+id/autotext"
  />

public class MainActivity extends Activity {
private AutoCompleteTextView autotext;
private ArrayAdapter<String> arrayAdapter;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.test);

    autotext =(AutoCompleteTextView) findViewById(R.id.autotext);
    String [] arr={"aa","aab","aac"};
    arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,arr);
    autotext.setAdapter(arrayAdapter);
  }

}