android:completionThreshold="1"：这里我们设置了输入一个字就显示提示

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:gravity="center"

    tools:context=".MainActivity">

    <AutoCompleteTextView

        android:id="@+id/actv_show"

        android:layout_marginRight="20dp"

        android:layout_marginLeft="20dp"

        android:completionThreshold="1"

        android:textColor="#000000"

        android:layout_width="match_parent"

        android:layout_height="wrap_content" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>

<TextView xmlns:android="http://schemas.android.com/apk/res/android"

    android:id="@android:id/text1"

    style="?android:attr/dropDownItemStyle"

    android:textAppearance="?android:attr/textAppearanceLargePopupMenu"

    android:singleLine="true"

    android:layout_width="match_parent"

    android:textColor="#000000"

    android:layout_height="?android:attr/listPreferredItemHeight"

    android:ellipsize="marquee" />

package com.example.administrator.test59autocompletetextview;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.ArrayAdapter;

import android.widget.AutoCompleteTextView;

public class MainActivity extends AppCompatActivity {

    private static final String[] data = new String[]{

            "小猪猪", "小狗狗", "小鸡鸡", "小猫猫", "小咪咪"

    };

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        //找到AutoCompleteTextView控件

        AutoCompleteTextView actv_show=findViewById(R.id.actv_show);

        //采用数组适配器，第一个参数是上下文，就是当前的Activity, 第二个参数是自己定义的一个布局，它里面只有一个TextView，第三个参数就是我们要显示的数据。

        ArrayAdapter<String> adapter2 = new ArrayAdapter<String>(getApplicationContext(), R.layout.actv_layout, data);

        actv_show.setAdapter(adapter2);

    }

}