ExpandableListView

使用基于ListView的扩展组件ExpandableListView制作类似QQ好友的列表
这里会用到SimpleExpandableListAdapter这个适配器
首先看一下这个适配器的构造方法

/**
 * Constructor
 *
 * @param context The context where the {@link ExpandableListView}
 *            associated with this {@link SimpleExpandableListAdapter} is
 *            running
 * @param groupData A List of Maps. Each entry in the List corresponds to
 *            one group in the list. The Maps contain the data for each
 *            group, and should include all the entries specified in
 *            "groupFrom"
 * @param groupFrom A list of keys that will be fetched from the Map
 *            associated with each group.
 * @param groupTo The group views that should display column in the
 *            "groupFrom" parameter. These should all be TextViews. The
 *            first N views in this list are given the values of the first N
 *            columns in the groupFrom parameter.
 * @param groupLayout resource identifier of a view layout that defines the
 *            views for a group. The layout file should include at least
 *            those named views defined in "groupTo"
 * @param childData A List of List of Maps. Each entry in the outer List
 *            corresponds to a group (index by group position), each entry
 *            in the inner List corresponds to a child within the group
 *            (index by child position), and the Map corresponds to the data
 *            for a child (index by values in the childFrom array). The Map
 *            contains the data for each child, and should include all the
 *            entries specified in "childFrom"
 * @param childFrom A list of keys that will be fetched from the Map
 *            associated with each child.
 * @param childTo The child views that should display column in the
 *            "childFrom" parameter. These should all be TextViews. The
 *            first N views in this list are given the values of the first N
 *            columns in the childFrom parameter.
 * @param childLayout resource identifier of a view layout that defines the
 *            views for a child. The layout file should include at least
 *            those named views defined in "childTo"
 */
public SimpleExpandableListAdapter(Context context,
        List<? extends Map<String, ?>> groupData, int groupLayout,
        String[] groupFrom, int[] groupTo,
        List<? extends List<? extends Map<String, ?>>> childData,
        int childLayout, String[] childFrom, int[] childTo) {
    this(context, groupData, groupLayout, groupLayout, groupFrom, groupTo, childData,
            childLayout, childLayout, childFrom, childTo);
}

里面有九个参数，可以说参数比较多，但是不要慌，理解了之后就会感觉很简单
第一个参数是上下文对象，第二个是group分组的数据源，第三个是组的布局界面，第四个是分组的数据源的map集合中的key的数组信息，第五个是要填写数据的组件数组，剩下的四个是描述子分组的信息的，和之前的group很类似
首先建立三个布局：
1.　item_group.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:gravity="center">

    <TextView
        android:id="@+id/tv_group"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="17sp"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

分组布局，将字号调到了17，显得大一些(默认15)，并且让其居中显示
2.　item_child.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:gravity="center">

    <TextView
        android:id="@+id/tv_child"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="#222121"
        android:textSize="13sp"
        android:layout_marginStart="38dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

这里将字号调小一点，并且颜色设置深一点，距离左边宽一点，便于区分
3.　activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
    tools:context=".MainActivity">

    <ExpandableListView
        android:id="@+id/expandable_ListView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>
</android.support.constraint.ConstraintLayout>

然后写MainActivity：

package com.fitsoft;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ExpandableListView;
import android.widget.SimpleExpandableListAdapter;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class MainActivity extends AppCompatActivity {

    ExpandableListView expandableListView;

    String[] groupStringArr = {"腾讯", "百度", "阿里巴巴"};

    String[][] childStringArr = {
            {"QQ","微信","QQ浏览器"},
            {"百度搜索","百度地图","百度外卖"},
            {"淘宝","支付宝","天猫商城"}
    };

    List<List<Map<String, ?>>> childData = new ArrayList<>();

    List<Map<String, ?>> groupData = new ArrayList<>();

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

        expandableListView = findViewById(R.id.expandable_ListView);

        //将groupStringArr中的数据放入groupData中
        for(int i=0; i<groupStringArr.length; i++){
            Map<String, String> map = new HashMap<>();
            //为了方便，只用一个key
            map.put("groupName", groupStringArr[i]);
            groupData.add(map);
            List<Map<String, ?>> itemList = new ArrayList<>();
            //二维数组将childStringArr中的数据放入childData中
            for(int j=0; j<childStringArr[i].length; j++){
                Map<String, String> map1 = new HashMap<>();
                map1.put("itemName", childStringArr[i][j]);
                itemList.add(map1);
            }
            childData.add(itemList);
        }

        //设置适配器
        SimpleExpandableListAdapter adapter = new SimpleExpandableListAdapter(this, groupData,
                R.layout.item_group, new String[]{"groupName"}, new int[]{R.id.tv_group},
                childData, R.layout.item_child, new String[]{"itemName"}, new int[]{R.id.tv_child});

        //绑定
        expandableListView.setAdapter(adapter);


    }

}

效果图：