(Andorid基础)ListView控件的使用--BasicAdapter

ListView可用与列表展示数据

数据设配器是数据与视图之间的桥梁

BasicAdapter是最基本的适配器

使用示例：

创建总列表数据试图 activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
    android:layout_width="match_parent"
    android:layout_height="45dp"
    android:text="手机商城"
    android:textSize="18sp"
    android:textColor="#FFFFFF"
    android:background="#FF8F03"
    android:gravity="center"
    />
    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/lv"/>
</LinearLayout>

当然还有单个列表元素的布局文件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp">
    <ImageView
        android:layout_width="120dp"
        android:layout_height="90dp"
        android:id="@+id/iv"
        android:layout_centerVertical="true"/>
    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="10dp"
        android:layout_toRightOf="@+id/iv"
        android:layout_centerVertical="true"
        >
        <TextView
            android:id="@+id/title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="桌子"
            android:textSize="20sp"
            android:textColor="#000000"
            />
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="价格:"
            android:id="@+id/tv_price"
            android:textSize="20sp"
            android:layout_marginTop="10dp"
            android:layout_below="@id/title"
            android:textColor="#FF8F03"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/price"
            android:text="1000"
            android:textSize="20sp"
            android:layout_below="@+id/title"
            android:layout_toRightOf="@id/tv_price"
            android:textColor="#FF8F03"
            android:layout_marginTop="10dp"
            />
    </RelativeLayout>
</RelativeLayout>

创建逻辑处理类：
MainActivity.java:

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    private ListView myListView;
    //初始化商品与价格
    private String[]  titles = {"桌子" , "苹果" ,"蛋糕","香蕉","菠萝","榴莲"};
    private String[]  prices = {"100$" , "15$" ,"14$","14$","19$","18$"};
    private int[] icons = {R.drawable.ic_launcher_foreground,R.drawable.ic_launcher_foreground,R.drawable.ic_launcher_foreground,R.drawable.ic_launcher_foreground,R.drawable.ic_launcher_foreground,R.drawable.ic_launcher_foreground};

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


        myListView = (ListView)findViewById(R.id.lv);

        MyBaseAdapter myBaseAdapter = new MyBaseAdapter();
        myListView.setAdapter(myBaseAdapter);
    }
    class  MyBaseAdapter  extends BaseAdapter {
        @Override
        public int getCount() {
            return titles.length;
        }
        @Override
        public Object getItem(int position) {
            return titles[position];
        }
        @Override
        public long getItemId(int position) {
            return position;
        }
        //每一个li
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder = null;
            if (convertView==null){
                convertView =  View.inflate(MainActivity.this,R.layout.list_item,null);
                //加载布局文件

                holder = new ViewHolder();
                holder.title = ((TextView) convertView.findViewById(R.id.title));
                holder.price = ((TextView) convertView.findViewById(R.id.price));
                holder.iv = ((ImageView) convertView.findViewById(R.id.iv));
                convertView.setTag(holder);
            }else {
                holder = (ViewHolder) convertView.getTag();
            }
            holder.title.setText(titles[position]);
            holder.price.setText(prices[position]);
            holder.iv.setBackgroundResource(icons[position]);
            return convertView;
        }
    }
    class ViewHolder{
        TextView title ,price;
        ImageView iv;
    }
}

说明：
1.自定义MyBaseAdapter类，继承BasieAdapter，实现四个方法，设置自己的数据属性
2.getView方法中，position参数为当前view的索引 convertView用于复用旧视图，parent用于设置布局文件
3.ViewHolder类用于复用旧视图
4.getView方法中判断 第一次加载的时候将视图缓存到convertView里，之后调用的都是缓存里的.