Android学习——控件ListView的使用

一、ListView的简单用法

首先新建一个ListViewTest项目，并让Android Studio自动创建好活动。然后修改activity_main.xml中的代码，如下：

<?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">

   <ListView
       android:id="@+id/list_view"
       android:layout_width="match_parent"
       android:layout_height="match_parent">
   </ListView>
</LinearLayout>

接下来修改MainActivity中的代码：

public class MainActivity extends AppCompatActivity {

    private String[] data={"Apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry","Cherry","Mango","Apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry","Cherry","Mango"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ArrayAdapter<String> adapter=new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_list_item_1,data);
        ListView listview=(ListView)findViewById(R.id.list_view);
        listview.setAdapter(adapter);
    }
}

数组中的数据无法直接传递给ListView，需要借助适配器来实现。

ArrayAdapter的构造函数中依次传入当前上下文，ListView子项布局的id，以及要适配的数据；

调用ListView的setAdapter()方法，将构建好的适配器对象传递进去，这样ListView和数据之间的关联就建立完成。

运行程序，可以通过滚动的方式来查看屏幕外的数据。

二、定制ListView的界面

首先准备一组图片，分别对应上面提供的每一种水果（注意图片大小尽量一致），放在drawable目录下，注意命名不能出现大写字母（比如Apple不合法）；

在com.example.administrator.listviewtest下新建.java文件，定义一个实体类Fruit，作为ListView适配器的适配类型。

public class Fruit{
    private String name;
    private int imageId;
    public Fruit(String name,int imageId){
        this.name=name;
        this.imageId=imageId;
    }
    public String getName(){
        return name;
    }
    public int getImageId(){
        return imageId;
    }
}

然后为ListView的子项指定一个自定义布局，在layout目录下新建fruit_item.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="wrap_content">

    <ImageView
        android:id="@+id/fruit_image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/fruit_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"
        />
</LinearLayout>

接下来创建一个自定义的适配器，同样在com.example.administrator.listviewtest下新建.java文件，重写了父类的一组构造函数，用于将上下文、ListView子项布局的id和数据都传递进来，命名为FruitAdapter，代码如下：

public class FruitAdapter extends ArrayAdapter<Fruit> {
    private int resourceId;
    public FruitAdapter(Context context, int textViewResourceId, List<Fruit> objects){
        super(context,textViewResourceId,objects);
        resourceId=textViewResourceId;
    }
    @Override
    public View getView(int position,View convertView,ViewGroup parent){
        Fruit fruit=getItem(position);           //获取当前项的实例
        View view= LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
        ImageView fruitImage=(ImageView)view.findViewById(R.id.fruit_image);
        TextView fruitName=(TextView) view.findViewById(R.id.fruit_name);
        fruitImage.setImageResource(fruit.getImageId());
        fruitName.setText(fruit.getName());
        return view;
    }
}

下面修改MainActivity中的代码：

package com.example.administrator.listviewtest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    private List<Fruit> fruitList=new ArrayList<>();

//  private String[] data={"Apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry","Cherry","Mango","Apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry","Cherry","Mango"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();                 //初始化水果数据
        FruitAdapter adapter=new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);

//      ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, data);
        ListView listview = (ListView) findViewById(R.id.list_view);
        listview.setAdapter(adapter);
    }

    private void initFruits(){
        for(int i=0;i<2;i++){
            Fruit apple=new Fruit("Apple",R.drawable.apple);
            fruitList.add(apple);
            Fruit orange=new Fruit("Orange",R.drawable.orange);
            fruitList.add(orange);
            Fruit banana=new Fruit("Banana",R.drawable.banana);
            fruitList.add(banana);
            Fruit waterlenmo=new Fruit("Waterlemon",R.drawable.waterlemon);
            fruitList.add(waterlenmo);
            Fruit pear=new Fruit("Pear",R.drawable.pear);
            fruitList.add(pear);
            Fruit grape=new Fruit("Grape",R.drawable.grape);
            fruitList.add(grape);
            Fruit pineapple=new Fruit("Pineapple",R.drawable.pineapple);
            fruitList.add(pineapple);
            Fruit strawberry=new Fruit("Strawberry",R.drawable.straw);
            fruitList.add(strawberry);
            Fruit cherry=new Fruit("Cherry",R.drawable.cherry);
            fruitList.add(cherry);
            Fruit mango=new Fruit("mango",R.drawable.mango);
            fruitList.add(mango);
        }
    }
}

运行程序后，效果图如下（图片大小后来才意识到，懒得换了……）：