Android开发 ExpandableListView 列表内容下拉View详解

前言

　　在需要实现一个List的item需要包含列表的时候,我们就可以选择ExpandableListView. 其实这个View的原始设计还是ListView的那套.就是增加2层的ListView而已.所以在写它的适配器与ListView的适配器挺相似的,所以会有一个通病就是没有Item的View的复用机制请一定要注意这点,在实现使用的时候需要写Item的View的复用,减少内存与增加性能.

一个简单的Demo

　　老规矩,先来一个最简单的demo来了解下最基本的使用方法.注意!这个demo是没有在Adapter写任何View复用机制的请不要用到实际项目中. demo只是帮助你快速认识了解ExpandableListView

效果图

　　

Activity的Xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <ExpandableListView
        android:id="@+id/expandablelistview"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </ExpandableListView>

</LinearLayout>

一级Item和二级Item用的xml布局

偷懒,我让一级和二级都使用一个布局

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/text1"
    android:layout_width="match_parent"
    android:layout_height="45dp"
    android:text="内容"
    android:textSize="15sp"
    android:textColor="@color/fontBlack3"
    android:gravity="center"
    android:background="@color/colorWhite">
</TextView>

编写适配器

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;
import java.util.List;

public class DemoAdapter extends BaseExpandableListAdapter {
    List<String> mGroupList;//一级List
    List<List<String>> mChildList;//二级List 注意!这里是List里面套了一个List<String>,实际项目你可以写一个pojo类来管理2层数据


    public DemoAdapter(List<String> groupList, List<List<String>> childList){
        mGroupList = groupList;
        mChildList = childList;

    }

    @Override
    public int getGroupCount() {//返回第一级List长度
        return mGroupList.size();
    }

    @Override
    public int getChildrenCount(int groupPosition) {//返回指定groupPosition的第二级List长度
        return mChildList.get(groupPosition).size();
    }

    @Override
    public Object getGroup(int groupPosition) {//返回一级List里的内容
        return mGroupList.get(groupPosition);
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {//返回二级List的内容
        return mChildList.get(groupPosition).get(childPosition);
    }

    @Override
    public long getGroupId(int groupPosition) {//返回一级View的id 保证id唯一
        return groupPosition;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {//返回二级View的id 保证id唯一
        return groupPosition + childPosition;
    }

    /**
     * 指示在对基础数据进行更改时子ID和组ID是否稳定
     * @return
     */
    @Override
    public boolean hasStableIds() {
        return true;
    }

    /**
     *  返回一级父View
     */
    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        convertView = LayoutInflater.from(parent.getContext()).inflate(R.layout.text_item, parent,false);
        ((TextView)convertView).setText((String)getGroup(groupPosition));
        return convertView;
    }

    /**
     *  返回二级子View
     */
    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        convertView = LayoutInflater.from(parent.getContext()).inflate(R.layout.text_item, parent,false);
        ((TextView)convertView).setText((String)getChild(groupPosition,childPosition));
        return convertView;
    }

    /**
     *  指定位置的子项是否可选
     */
    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}

Activity里的代码

        mExpandableListView = findViewById(R.id.expandablelistview);

        List<String> groupList = new ArrayList<>();
        groupList.add("一");
        groupList.add("二");
        groupList.add("三");

        List<List<String>> childList = new ArrayList<>();
        List<String> childList1 = new ArrayList<>();
        childList1.add("1");
        childList1.add("1");
        childList1.add("1");
        List<String> childList2 = new ArrayList<>();
        childList2.add("2");
        childList2.add("2");
        childList2.add("2");
        List<String> childList3 = new ArrayList<>();
        childList3.add("3");
        childList3.add("3");
        childList3.add("3");

        childList.add(childList1);
        childList.add(childList2);
        childList.add(childList3);

        DemoAdapter demoAdapter = new DemoAdapter(groupList, childList);
        mExpandableListView.setAdapter(demoAdapter);

        mExpandableListView.setOnGroupClickListener(new ExpandableListView.OnGroupClickListener() {//一级点击监听
            @Override
            public boolean onGroupClick(ExpandableListView parent, View v, int groupPosition, long id) {

                //如果你处理了并且消费了点击返回true,这是一个基本的防止onTouch事件向下或者向上传递的返回机制
                return false;
            }
        });

        mExpandableListView.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {//二级点击监听
            @Override
            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {

                //如果你处理了并且消费了点击返回true
                return false;
            }
        });

其他Xml属性

android:dividerHeight="20dp" 设置边距高度,注意设置这个边距包括了一级和二级

android:divider="@color/colorRed1" 设置一级边距的背景色

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