ListView控件学习

1、在布局中加入ListView

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

</LinearLayout>

2、一个ListView的创建需要3个元素

1. ListView中的每一列的View。
2. 填入View的数据或者图片等。
3. 连接数据与ListView的适配器。

   　　 private String[]data={
            "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);
        }

 2、定制ListView的界面

首先定义一个实体类，作为ListView适配器的适配类型。

package com.example.listviewtest;

public class Fruit {
    private String name;//水果的名字
    private int imageId;//水果对应图片的资源id
    public Fruit(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }
    public String getName() {
        return name;
    }
    public int getImageId() {
        return imageId;
    }
    
}

2、为ListView的子项指定一个我们自定义的布局 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="match_parent"
    >
    
    <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"
           android:layout_marginLeft="10dip"/>
</LinearLayout>

3、自定义一个适配器，这个适配器继承自ArrayAdapter，并指出泛型为Fruit类。

在实际开发中LayoutInflater这个类还是非常有用的，它的作用类似于findViewById()。不同点是 LayoutInflater是用来找res/layout/下的xml布局文件，并且实例化；而findViewById()是找xml布局文件下的具 体widget控件(如Button、TextView等)。

具体作用：

• 对于一个没有被载入或者想要动态载入的界面，都需要使用LayoutInflater.inflate()来载入；
• 对于一个已经载入的界面，就可以使用Activiyt.findViewById()方法来获得其中的界面元素。

LayoutInflater 是一个抽象类，在文档中如下声明：

public abstract class LayoutInflater extends Object

获得 LayoutInflater 实例的三种方式

• LayoutInflater inflater = getLayoutInflater();//调用Activity的getLayoutInflater() 
• LayoutInflater inflater = LayoutInflater.from(context);  
• LayoutInflater inflater =  (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE)

package com.example.listviewtest;

import java.util.List;

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

public class FruitAdapter extends ArrayAdapter<Fruit>{
    
    private int resourceID;
    public FruitAdapter(Context context,  int textViewResourceId,
            List<Fruit> objects) {
        super(context,  textViewResourceId, objects);
        // TODO Auto-generated constructor stub
        resourceID=textViewResourceId;
    }
    
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        Fruit fruit=getItem(position);
        View view=LayoutInflater.from(getContext()).inflate(resourceID, null);
        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;
    }
    
}

4、MainActivity

package com.example.listviewtest;

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

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends Activity {
    
    private List<Fruit> fruitList=new ArrayList<Fruit>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        FruitAdapter adapter=new FruitAdapter(MainActivity.this, R.layout.fruit_item, fruitList);
        ListView listView=(ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }
    private void initFruits() {
        Fruit apple = new Fruit("Apple", R.drawable.apple_pic);
        fruitList.add(apple);
        Fruit banana = new Fruit("Banana", R.drawable.banana_pic);
        fruitList.add(banana);
        Fruit orange = new Fruit("Orange", R.drawable.orange_pic);
        fruitList.add(orange);
        Fruit watermelon = new Fruit("Watermelon", R.drawable.watermelon_pic);
        fruitList.add(watermelon);
        Fruit pear = new Fruit("Pear", R.drawable.pear_pic);
        fruitList.add(pear);
        Fruit grape = new Fruit("Grape", R.drawable.grape_pic);
        fruitList.add(grape);
        Fruit pineapple = new Fruit("Pineapple", R.drawable.pineapple_pic);
        fruitList.add(pineapple);
        Fruit strawberry = new Fruit("Strawberry", R.drawable.strawberry_pic);
        fruitList.add(strawberry);
        Fruit cherry = new Fruit("Cherry", R.drawable.cherry_pic);
        fruitList.add(cherry);
        Fruit mango = new Fruit("Mango", R.drawable.mango_pic);
        fruitList.add(mango);
    }
    
}

 5、提升ListView的运行效率

FruitAdapter的getView()方法每次都将布局重新加载一遍，当ListView快速滚动的时候就会成为性能的瓶颈。getView()方法中还有一个convertView参数，这个参数用于将之前加载好的布局进行缓存，以便之后可以进行重用。viewHolder类就是一个持有者的类，他里面一般没有方法，只有属性，作用就是一个临时的储存器，把你getView方法中每次返回的View存起来，可以下次再用

package com.example.listviewtest;

import java.util.List;

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

public class FruitAdapter extends ArrayAdapter<Fruit>{
    
    private int resourceID;
    public FruitAdapter(Context context,  int textViewResourceId,
            List<Fruit> objects) {
        super(context,  textViewResourceId, objects);
        // TODO Auto-generated constructor stub
        resourceID=textViewResourceId;
    }
    
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        Fruit fruit=getItem(position);
        View view;
        ViewHolder viewHolder;
        if(convertView==null){
         view=LayoutInflater.from(getContext()).inflate(resourceID, null);
         viewHolder=new ViewHolder();
         viewHolder.imageView=(ImageView) view.findViewById(R.id.fruit_image);
         viewHolder.textView=(TextView) view.findViewById(R.id.fruit_name);
         view.setTag(viewHolder);//将ViewHolder存储在view中
        }else{
            view=convertView;
            viewHolder=(ViewHolder) view.getTag();//重新获取ViewHolder
        }
        viewHolder.imageView.setImageResource(fruit.getImageId());
        viewHolder.textView.setText(fruit.getName());
        return view;
    }
    class ViewHolder{
        ImageView imageView;
        TextView textView;
    }
    
}

 6、ListView的点击事件

        listView.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> arg0, View arg1, int position,
                    long id) {
                Fruit fruit=fruitList.get(position);
                Toast.makeText(MainActivity.this, fruit.getName(), Toast.LENGTH_SHORT).show();
                
            }
            
        });