ExpandableListView & ExpandableListAdapter

一、相关知识简介：

1、ExpandableListView是什么：ExpandableListView是一个垂直滚动显示两级列表项的视图，与ListView不同的是，它可以有两层：每一层都能够被独立的展开并显示其子项。这些子项来自于与该视图关联的ExpandableListAdapter。

2、继承ExpandableListAdapter后必须重写的方法及其“含义”：简书介绍的很详细：https://www.jianshu.com/p/cb0812a9bd85

3、案例：好友分类显示界面：

4、ExpandableListView的xml布局：

<?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">
    <ExpandableListView
        android:id="@+id/exp"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout>

5、数据组的xml布局：

<?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:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/group_name"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:layout_marginLeft="60dp"
        android:padding="10dp"
        android:textSize="24dp"
        tools:text="000" />
</LinearLayout>

6、数据组下数据项的xml布局：

<?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:id="@+id/child_name"
        android:layout_width="match_parent"
        android:layout_height="45dp"
        android:layout_marginLeft="60dp"
        android:layout_marginTop="5dp"
        android:layout_marginBottom="5dp"
        android:padding="5dp"
        android:textColor="#f00"
        android:textSize="20dp"/>

</LinearLayout>

7、自定义适配器（继承自ExpandableListAdapter）

package com.me.adapter;

import android.graphics.Color;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;

import com.me.androidstudy.R;

public class ExpAdapter extends BaseExpandableListAdapter {
    private String [] group ;
    private String [] [] child ;

    public void setChild(String[][] child) {
        this.child = child;
    }

    public void setGroup(String[] group) {
        this.group = group;
    }

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

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

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

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

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition * 100;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return groupPosition * 100 + childPosition;
    }

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

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        View inflate = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_group, null);
        TextView group_name = inflate.findViewById(R.id.group_name);
        group_name.setText((String)getGroup(groupPosition));
        return inflate;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        View inflate = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_child, null);
        TextView child_name = inflate.findViewById(R.id.child_name);
        child_name.setText((String)getChild(groupPosition,childPosition));
        if(childPosition>1){
            child_name.setTextColor(Color.BLACK);
        }
        return inflate;
    }

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

8、逻辑代码：（activity）

package com.me.androidstudy;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ExpandableListView;

import androidx.annotation.Nullable;

import com.me.adapter.ExpAdapter;

public class Activity_exp extends Activity {
    ExpandableListView exp ;
    ExpAdapter adapter = new ExpAdapter();
    public void initView(){
        exp = findViewById(R.id.exp);
    }

    public void action(){
        String[] group = {"我的好友","宿舍","朋友","特别关心"};
        String[] [] child = {
                {"狂神","麦子","红钻","青岛"},
                {"一鸣","不举","胖鑫","舍长"},
                {"晓","恶霸","孟招","笑天"},
                {"风","花","雪","月"}
        };
        adapter.setGroup(group);
        adapter.setChild(child);
        exp.setAdapter(adapter);
    }

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_exp);
        initView();
        action();
    }
}