ListView 及适配器的应用

ListView的应用【包含Adapter的应用】

1. 父容器和子view

   【main_activity.xml】

   <?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:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:orientation="vertical"
           android:fitsSystemWindows="true">
       <ListView
           android:id="@+id/lv_hobby"
           android:layout_width="match_parent"
           android:layout_height="match_parent"/>
   </LinearLayout>

   【hobby_item.xml】

   <?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">
           <RelativeLayout
               android:layout_width="wrap_content"
               android:layout_height="wrap_content"
               android:orientation="horizontal">
               <TextView
                   android:id="@+id/hobby"
                   android:layout_width="wrap_content"
                   android:layout_height="wrap_content"/>
               <CheckBox
                   android:id="@+id/checkbox"
                   android:layout_width="wrap_content"
                   android:layout_height="wrap_content"
                   android:layout_alignParentEnd="true"/>
           </RelativeLayout>
   </LinearLayout>

2. item封装-->Hobby.java

   package com.neostra.test;
   ​
   public class Hobby {
       private String hobby;
   ​
       public Hobby(String hobby) {
           this.hobby = hobby;
       }
   ​
       public String getHobby() {
           return hobby;
       }
   ​
       public void setHobby(String hobby) {
           this.hobby = hobby;
       }
   ​
       @Override
       public String toString() {
           return "Hobby{" +
                   "hobby='" + hobby + '\'' +
                   '}';
       }
   }

3. 子view（hobby_item）适配器--->HobbyAdapter.java

   package com.neostra.test;
   ​
   import android.content.Context;
   import android.view.LayoutInflater;
   import android.view.View;
   import android.view.ViewGroup;
   import android.widget.BaseAdapter;
   import android.widget.CheckBox;
   import android.widget.TextView;
   ​
   import java.util.ArrayList;
   ​
   public class HobbyAdapter extends BaseAdapter {
       private ArrayList<Hobby> dataList;//适配器数据源
       private Context mContext;
   ​
       public HobbyAdapter(ArrayList<Hobby> dataList, Context mContext) {
           this.dataList = dataList;
           this.mContext = mContext;
       }
   //item长度
       @Override
       public int getCount() {
           return dataList.size();
       }
   ​
   //item项
       @Override
       public Object getItem(int i) {
           return dataList.get(i);
       }
   ​
       @Override
       public long getItemId(int i) {
           return 0;
       }
   //获取item，放回匹配的视图
       @Override
       public View getView(int i, View view, ViewGroup viewGroup) {
           MyViewHolder myViewHolder=null;//什么内部类Holder对象
           //判断xml视图是否已存在view当中
           if (view == null){
               view = View.inflate(mContext,R.layout.hobby_item,null);
               TextView hobby=view.findViewById(R.id.hobby);
               CheckBox checkedBox=view.findViewById(R.id.checkbox);
               myViewHolder = new MyViewHolder(hobby,checkedBox);
               view.setTag(myViewHolder);//将myViewHolder存储到view当中，从而不用getView时都新建子view中的控件
           }else {
               myViewHolder=(MyViewHolder) view.getTag();//若view不为空，则获取到子viewHolder类
           }
           myViewHolder.hobby.setText(dataList.get(i).getHobby());//动态设置子view显示效果
           return view;
       }
       //视图holder类
       static class MyViewHolder{
           private TextView hobby;
           private CheckBox checkBox;
   ​
           public MyViewHolder(TextView hobby, CheckBox checkBox) {
               this.hobby = hobby;
               this.checkBox = checkBox;
           }
       }
   }
   ​

4. MainActivity.java

   package com.neostra.test;
   ​
   import androidx.appcompat.app.AppCompatActivity;
   import androidx.recyclerview.widget.DividerItemDecoration;
   import androidx.recyclerview.widget.GridLayoutManager;
   import androidx.recyclerview.widget.LinearLayoutManager;
   import androidx.recyclerview.widget.RecyclerView;
   ​
   import android.os.Bundle;
   import android.util.Log;
   import android.widget.GridLayout;
   import android.widget.GridView;
   import android.widget.LinearLayout;
   import android.widget.ListView;
   ​
   import java.time.LocalDate;
   import java.util.ArrayList;
   import java.util.List;
   ​
   public class MainActivity extends AppCompatActivity {
       private ListView lv_honbby;
       private HobbyAdapter hobbyAdapter;
       private ArrayList<Hobby> dataList;//适配数据准备
   ​
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
           dataList = new ArrayList<Hobby>();//数据源准备
           dataList.add(new Hobby("math"));
           dataList.add(new Hobby("English"));
           dataList.add(new Hobby("chinese"));
           dataList.add(new Hobby("chinese"));
           lv_hobby = findViewById(R.id.lv_hobby);
           hobbyAdapter = new HobbyAdapter(dataList, this);//适配器准备
           lv_hobby.setAdapter(hobbyAdapter);//为listview视图设置适配器
       }
   ​
   }

5.