布局:
    <AutoCompleteTextView
        android:id="@+id/searchid"
        android:layout_width="300dp"
        android:layout_height="50dp"
        android:layout_marginStart="32dp"
        android:layout_marginTop="50dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:completionThreshold="2"
        android:hint="请输入搜索的文字"/>

实现:
        /// 创建AutoCompleteTextView对象
        AutoCompleteTextView search = (AutoCompleteTextView)findViewById(R.id.searchid);


        /// 设置数据源数组
        String[] arrays = {"beijing1","beijing1","beijing1","beijing1","beijing1"};

        // 设置适配器
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arrays);

        // 将适配器与当前AutoCompleteTextView控件绑定
        search.setAdapter(adapter);

总结四步:
1. 获取AutoCompleteTextView对象
2.设置数据源
3.设置适配器
4.将适配器和控件绑定

效果图:

Untitled.gif