Android-ListView

常用属性

1. listSelector: 当条目被点击后，改变条目的背景颜色
2. divider: 设置分割线的颜色
3. dividerHeight: 设置分割线的高度
4. srcollbars: 是否显示滚动条
5. fadingEdge: 去掉上下黑色阴影

简单的ListView

资源文件下载

创建布局(activity_main.xml)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <LinearLayout
        android:layout_width="match_parent"
        android:orientation="horizontal"
        android:background="#336633"
        android:gravity="center_vertical"
        android:layout_height="80dp">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="20sp"
            android:id="@+id/listTitle"
            android:layout_marginLeft="20dp"
            android:textColor="@color/white"
            android:textStyle="bold"
            android:text="TITLE"/>
    </LinearLayout>
    <ListView
        android:layout_width="match_parent"
        android:id="@+id/listView"
        android:layout_height="match_parent"/>
</LinearLayout>

创建列表项布局(item.xml)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_height="100dp"
    android:layout_width="match_parent"
    android:orientation="horizontal"
    android:gravity="center_vertical"
    android:background="#339933"
    xmlns:android="http://schemas.android.com/apk/res/android">
<!--    任意一张图片做默认图片即可-->
    <ImageView
        android:layout_width="80dp"
        android:layout_marginLeft="10dp"
        android:src="@mipmap/moren"
        android:id="@+id/foodIcon"
        android:layout_height="80dp"/>
    <TextView
        android:text="foodName"
        android:layout_marginLeft="20dp"
        android:textColor="@color/white"
        android:textSize="20sp"
        android:textStyle="bold"
        android:id="@+id/foodName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

创建MyListTest类，该类继承自BaseAdapter，ListView的适配器

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MyAdapter extends BaseAdapter {
    private String[] foodName;
    private int[] foodIcon;
    private Context context;
    public MyAdapter(String[] foodName,int[] foodIcon,Context context){
        this.context = context;
        this.foodIcon = foodIcon;
        this.foodName = foodName;
    }
    @Override
//    返回列表的总列数
    public int getCount() {
        return foodIcon.length;
    }

    @Override
//    返回Item的数据对象
    public Object getItem(int position) {
        return null;
    }

    @Override
//    //返回item的id
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
//        如果没有拿到过ite资源文件
        if (convertView == null){
            convertView = View.inflate(context,R.layout.item,null);
        }
//        从item中找到要设置的子控件
        TextView textView = convertView.findViewById(R.id.foodName);
        ImageView imageView = convertView.findViewById(R.id.foodIcon);
//        设置
        textView.setText(foodName[position]);
        imageView.setImageResource(foodIcon[position]);
        return convertView;
    }
}

在MainActivity中对ListView进行应用

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private int[] foodIcon = new int[]{
            R.mipmap.dangao,R.mipmap.cha,R.mipmap.hanbao,R.mipmap.jitui,R.mipmap.kafei,R.mipmap.kaixinguo,R.mipmap.lanmei,
            R.mipmap.ningmeng,R.mipmap.niupai,R.mipmap.pijiu,R.mipmap.pisa,R.mipmap.qiyiguo,R.mipmap.regou,R.mipmap.sanmingzhi,
            R.mipmap.shengnvguo,R.mipmap.shutiao,R.mipmap.tusi,R.mipmap.yimian,R.mipmap.yingtao,R.mipmap.zhangyuxiaowanzi
    };
    private String[] foodName = new String[]{
            "蛋糕","茶","汉堡","鸡腿","咖啡","开心果","蓝莓","柠檬","牛排","啤酒","披萨","奇异果","热狗","三明治","圣女果","薯条","吐司","意面","樱桃","章鱼小丸子"
    };
    private ListView listView;
    private TextView listTitle;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listView = findViewById(R.id.listView);
		listTitle = findViewById(R.id.listTitle);
        MyAdapter myAdapter = new MyAdapter(foodName,foodIcon,this);
        listView.setAdapter(myAdapter);
    }
}

ListView的item添加点击事件

在MainActivity中插入

//        给item添加事件
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                listTitle.setText(foodName[position]);
            }
        });

ListView的优化

优化原因：当滑动列表时，划出屏幕的item就会被摧毁掉，新出现的item就会创建一个新的view对象，并且findViewById也十分耗时

新知识点：setTag()是设置标签，getTag()是获取标签,经常用来存储一些view的数据(大概相当于js中setAttribute给标签添加属性)

在MyAdapter类中创建一个内部类

final class ViewHolder{
//    将item下需要调用的子控件全部填入
    TextView textView;
    ImageView imageView;
}

在MyListTest类的getView方法中使用ViewHolder类创建对象

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
//        声明viewHolder变量
        ViewHolder viewHolder;
        if (convertView == null){
//            创建ViewHolder对象
            viewHolder = new ViewHolder();
            convertView = View.inflate(context,R.layout.item,null);
//            将获取到的view赋值给viewHolder类的变量
            viewHolder.textView = convertView.findViewById(R.id.text1);
            viewHolder.imageView = convertView.findViewById(R.id.img1);
//            将viewHolder附加给convertView
            convertView.setTag(viewHolder);
        }
        else{
//            从convertView中取出viewHolder
            viewHolder = (ViewHolder) convertView.getTag();
        }
//        得到ViewHolder类变量的值
        viewHolder.textView.setText(iconName[position]);
        viewHolder.imageView.setImageResource(iconId[position]);
        return convertView;
    }

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