Android开发高级组件--ExpandableListView(可伸展的列表组件)

1、在Android开发中，有时候希望对列表项可以分组管理并实现收缩功能，例如QQ在使用时，有“我的好友”、“家人”、“同学”等分组，单击其中一项会展开，再单击一次又缩回去。要实现这种功能，就得使用到我们今天的主角ExpandableListView组件了。

2、该组件层次结构关系如下：
   java.lang.Object
      android.view.View
         android.view.ViewGroup
            android widget.AdapterView<T extends android.widget.Adapter>
               android.widget.AbsListView
                  android.widget.ListView
                     android.widget.ExpandableListView

3、每一个可扩展项旁边都有一个提示符（箭头等）用来说明该列表项目前的状态，可以使用方法：setChildIndicator(Drawable)和setGroupIndicator(Drawable)（或相应的XML文件的属性）去设置这些提示符的样式。注意：在XML布局文件中，一般不对ExpandableListView的android:layout_height属性使用wrap_content，否则可能会报错。
  与ListView一样ExpandableListView也需要一个适配器做桥梁来提供数据，ExpandableListView是一个垂直滚动显示两级列表项，它可以有两层，每层都能够独立的展开并显示其子项。BaseExpandableListAdapter是一个用在ExpandableListView组件的适配器。

4、创建布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:textSize="24sp"
        android:gravity="center"
        android:text="花名册"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

    <ExpandableListView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/list"
        android:background="#abcdef"/>

</LinearLayout>

5、修改ExpandableActivity.java文件
package xiao.fuyan.testapp;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.BaseExpandableListAdapter;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

/**
* Created by xiao on 2017/1/6.
*/
public class ExpandableActivity extends Activity {

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

        //
        ExpandableListAdapter adapter = new BaseExpandableListAdapter() {
            int[] logos = new int[]{R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher};
            private String[] generalsTypes = new String[]{"1", "2", "3"};

            private String[][] generals = new String[][]{
                    {"a", "b", "c", "d"},
                    {"e", "f", "g", "h"},
                    {"i", "j", "k", "l"}
            };
            private int[][] generalsLogos = new int[][]{
                    {R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher},
                    {R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher},
                    {R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher, R.mipmap.ic_launcher}
            };

            TextView getTextView(){
                AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
                    ViewGroup.LayoutParams.FILL_PARENT, 64
                );
                TextView textView = new TextView(ExpandableActivity.this);
                textView.setLayoutParams(lp);
                textView.setGravity(Gravity.CENTER_VERTICAL);
                textView.setPadding(36, 0, 0, 0);
                textView.setTextSize(16);
                textView.setTextColor(Color.BLACK);
                return textView;
            }

            @Override
            public int getGroupCount() {
                return generalsTypes.length;
            }

            @Override
            public int getChildrenCount(int groupPosition) {
                return generals[groupPosition].length;
            }

            @Override
            public Object getGroup(int groupPosition) {
                return generalsTypes[groupPosition];
            }

            @Override
            public Object getChild(int groupPosition, int childPosition) {
                return generals[groupPosition][childPosition];
            }

            @Override
            public long getGroupId(int groupPosition) {
                return groupPosition;
            }

            @Override
            public long getChildId(int groupPosition, int childPosition) {
                return childPosition;
            }

            @Override
            public boolean hasStableIds() {
                return true;
            }

            @Override
            public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
                LinearLayout ll = new LinearLayout(ExpandableActivity.this);
                ll.setOrientation(LinearLayout.HORIZONTAL);
                ImageView logo = new ImageView(ExpandableActivity.this);
                logo.setImageResource(logos[groupPosition]);
                logo.setPadding(20, 0, 0, 0);
                ll.addView(logo);
                TextView textView = getTextView();
                textView.setTextColor(Color.BLACK);
                textView.setText(getGroup(groupPosition).toString());
                ll.addView(textView);
                return ll;
            }

            @Override
            public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
                LinearLayout ll = new LinearLayout(ExpandableActivity.this);
                ll.setOrientation(LinearLayout.HORIZONTAL);
                ImageView generalLogo = new ImageView(ExpandableActivity.this);
                generalLogo.setImageResource(generalsLogos[groupPosition][childPosition]);
                ll.addView(generalLogo);
                TextView textView = getTextView();
                textView.setText(getChild(groupPosition, childPosition).toString());
                ll.addView(textView);
                return ll;
            }

            @Override
            public boolean isChildSelectable(int groupPosition, int childPosition) {
                return true;
            }
        };

        ExpandableListView expandableListView = (ExpandableListView)
                findViewById(R.id.list);
        expandableListView.setAdapter(adapter);


    }
}