使用BaseExpandableListAdapter 以实现的可折叠的所谓列表，例如QQ朋友们在分组功能。

基于BaseExpandableListAdapter扩大ExpandableList说明，今天，有两个主要的网上流行：第一种方法是BaseExpandableListAdapter传入两个数组，第一个是表示Group（文件夹头）信息的一维数组，第二个是表示Child（文件夹子项）的二维数组数组；另外一种是构建两个类，一个是表示文件夹信息的GroupInfo类。还有一个是表示子项信息的ChildInfo类，然后传入BaseExpandableListAdapter。通过对照发现，第一种方法因为数组是固定的。而实际项目中往往须要动态变化的文件夹和子项。因此用处不大。另外一种方法文件太多，实现复杂。这里提供一种方法，传递两个个动态的二维数组来实现文件夹结构。

package com.example.test;

import java.util.ArrayList;

import android.os.Bundle;

import android.app.Activity;

import android.graphics.Color;

import android.graphics.drawable.ColorDrawable;

import android.view.Gravity;

import android.view.Menu;

import android.view.View;

import android.view.ViewGroup;

import android.widget.BaseExpandableListAdapter;

import android.widget.ExpandableListAdapter;

import android.widget.ExpandableListView;

import android.widget.ImageView;

import android.widget.LinearLayout;

import android.widget.TextView;

import android.view.View.OnClickListener;

public class MainActivity extends Activity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        //Group数据

        ArrayList<String> groupList = new ArrayList<String>();

        groupList.add("我的好友");

        groupList.add("我的亲人");

        groupList.add("我的同学");

        //Child数据

        ArrayList<String> itemList1 = new ArrayList<String>();

        itemList1.add("小米");

        itemList1.add("小李");

        ArrayList<String> itemList2 = new ArrayList<String>();

        itemList2.add("小丽");

        itemList2.add("小小");

        itemList2.add("小可");

        ArrayList<String> itemList3 = new ArrayList<String>();

        itemList3.add("小南");

        itemList3.add("小飞");

        itemList3.add("小丁");

        itemList3.add("小美");

        ArrayList<ArrayList<String>> childList = new ArrayList<ArrayList<String>>();

        childList.add(itemList1);

        childList.add(itemList2);

        childList.add(itemList3);

        //可折叠List

        ExpandableListView list = new ExpandableListView(this);

        ExpandableListAdapter mAdapter = new MyExpandableListAdapter(groupList, childList);

        list.setAdapter(mAdapter);

        list.setCacheColorHint(0x00000000);

        list.setSelector(new ColorDrawable(Color.TRANSPARENT));

        list.setGroupIndicator(null);

        for (int i = 0; i < mAdapter.getGroupCount(); i++) {

            list.expandGroup(i);

        }

        setContentView(list);

    }

    //Adapter

    private class MyExpandableListAdapter extends BaseExpandableListAdapter {

        private ArrayList<String> groupList;

        private ArrayList<ArrayList<String>> childList;

        MyExpandableListAdapter(ArrayList<String> groupList, ArrayList<ArrayList<String>> childList) {

            this.groupList = groupList;

            this.childList = childList;

        }

        public Object getChild(int groupPosition, int childPosition) {

            return childList.get(groupPosition).get(childPosition);

        }

        private int selectedGroupPosition = -1;

        private int selectedChildPosition = -1;

        public void setSelectedPosition(int selectedGroupPosition, int selectedChildPosition) {

            this.selectedGroupPosition = selectedGroupPosition;

            this.selectedChildPosition = selectedChildPosition;

        }

        public long getChildId(int groupPosition, int childPosition) {

            return childPosition;

        }

        public int getChildrenCount(int groupPosition) {

            return childList.get(groupPosition).size();

        }

        public View getChildView(final int groupPosition, final int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {

            TextView textView = null;

            if (convertView == null) {

                textView = new TextView(MainActivity.this);

                textView.setPadding(32, 10, 0, 10);

                convertView = textView;

            } else {

                textView = (TextView) convertView;

            }

            textView.setText(getChild(groupPosition, childPosition).toString());

            if (groupPosition == selectedGroupPosition) {

                if (childPosition == selectedChildPosition) {

                    textView.setBackgroundColor(0xffb6ddee);

                } else {

                    textView.setBackgroundColor(Color.TRANSPARENT);

                }

            }

            textView.setOnClickListener(new OnClickListener() {

                public void onClick(View v) {

                    setSelectedPosition(groupPosition, childPosition);

                    notifyDataSetChanged();

                }

            });

            return textView;

        }

        public Object getGroup(int groupPosition) {

            return groupList.get(groupPosition);

        }

        public int getGroupCount() {

            return groupList.size();

        }

        public long getGroupId(int groupPosition) {

            return groupPosition;

        }

        public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {

            LinearLayout cotain = new LinearLayout(MainActivity.this);

            cotain.setPadding(0, 10, 0, 10);

            cotain.setGravity(Gravity.CENTER_VERTICAL);

            ImageView imgIndicator = new ImageView(MainActivity.this);

            TextView textView = new TextView(MainActivity.this);

            textView.setText(getGroup(groupPosition).toString());

            textView.setPadding(5, 0, 0, 0);

            if (isExpanded) {

                imgIndicator.setBackgroundResource(R.drawable.bg_arrow_up);

            } else {

                imgIndicator.setBackgroundResource(R.drawable.bg_arrow_down);

            }

            cotain.addView(imgIndicator);

            cotain.addView(textView);

            return cotain;

        }

        public boolean hasStableIds() {

            return true;

        }

        public boolean isChildSelectable(int groupPosition, int childPosition) {

            return true;

        }

    }

    @Override

    public boolean onCreateOptionsMenu(Menu menu) {

        getMenuInflater().inflate(R.menu.main, menu);

        return true;

    }

}

groupList 用于组名（类似QQ好友、同学、朋友），

childList 每个元素是一组子数据的（类似QQ同学约翰·史密斯，收集李四)