ExpandableLIstView,可展开的ListView

可以实现像qq好友分类一样的效果

 首先当然是需要在主界面的布局里面放一个ExpandableListView，因为我放东西喜欢在可视化界面里直接拖进去然后再去xml里面修改，这里我发现可视化界面里找不到这个组件，没办法只能手写，而且ExpandableListView好像只能放在线性布局里面，需要手动把初始的约束布局改成线性

接下来再做两个布局，一个用来加载分类栏，也就是外层的布局，一个用来加载内容栏，也就是内层的布局

外层布局

内层布局

 这里可以根据个人喜好让两个布局位置调一下

接下来就是最重要的逻辑部分，和listview一样，我们也用自制的适配器来实现，

 package com.example.expandblelistview;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
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.TextView;
import android.widget.Toast;

 public class MainActivity extends AppCompatActivity {
    private ExpandableListView listView;
     @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = findViewById(R.id.listView);
        listView.setAdapter(new MyExpandble());
         
        listView.setonChildClickListener(new ExpandableListView.onChildClickListener() {
            @Override
            public boolean onChildClick(ExpandableListView expandableListView, View view, int i, int i1, long l) {
                Toast.makeText(MainActivity.this,strings[i][i1],Toast.LENGTH_SHORT).show();
                return true;
            }
        });
    }

     private String[] groups = {"ss","dd","ff","ff"};
     private String[][] strings = {{"ee","rr","tt"},{"gg","kk","ll"},{"77","88","22"},{"agd","asgr","ger"}};

     
     class MyExpandble extends baseExpandableListAdapter {
        @Override
        //外层的长度
        public int getGroupCount() {
            return groups.length;
        }

        @Override
        //内层的长度
        public int getChildrenCount(int i) {
            return strings[i].length;
        }

        @Override
        //外层的内容
        public Object getGroup(int i) {
            return groups[i];
        }

        @Override
        //内层的内容
        public Object getChild(int i, int i1) {
            return strings[i][i1];
        }

        @Override
        //获得外层的id
        public long getGroupId(int i) {
            return i;
        }

        @Override
        //获得内层的id
        public long getChildId(int i, int i1) {
            return i;
        }

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

        @Override
        //加载外层的布局
        public View getGroupView(int i, boolean b, View view, ViewGroup viewGroup) {
            if (view == null){
                view = getLayoutInflater().inflate(R.layout.group,null);
            }
            ImageView icon = view.findViewById(R.id.imageView);
            TextView title = view.findViewById(R.id.textView);

            title.setText(groups[i]);
            return view;
        }

        @Override
        //加载内层的布局
        public View getChildView(int i, int i1, boolean b, View view, ViewGroup viewGroup) {
            if (view == null){
                view = getLayoutInflater().inflate(R.layout.child,null);
            }
            ImageView icon = view.findViewById(R.id.imageView1);
            TextView title = view.findViewById(R.id.textView1);
            title.setText(strings[i][i1]);
            return view;
        }

        @Override
        //内层是否能被选中
        public boolean isChildSelectable(int i, int i1) {
            return true;
        }
    }
}

 最终效果就实现了，