ListView提升运行效率及增加点击事件

一、直接上代码

1.Fruit.java

package com.zhc.listviewtest;

public class Fruit {
private String name;//成员变量name
private int imageId;

//这个构造函数在MainActivity中的初始化水果数据initFruits的会被重写，参数重新赋值。
public Fruit(String name, int imageId) {
	this.name = name;//将参数name赋值给成员变量name
	this.imageId = imageId;
}
public String getName() {
	return name;
}
public int getImageId() {
	return imageId;
}

}

2.fruit_item.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    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="10dp" />

</LinearLayout>

3.FruitAdappter.java

package com.zhc.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 FruitAdappter extends ArrayAdapter<Fruit> {
	private int resourceId;
	 

	// 重写父类ArrayAdapter的一组构造函数，用于将上下文、ListView子项布局的id和数据传递进来。
	public FruitAdappter(Context context, int textViewResourceId,
			List<Fruit> objects) {
		super(context, textViewResourceId, objects);
		resourceId = textViewResourceId;// textViewResourceId的值是在MainActivity里面传过来的R.layout.fruit_item
	}
/**
 * 1. 重写父类的getView方法，这个方法在每个子项被滚动到屏幕内的时候会被调用。
 * 2.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。
 * 3.ViewHolder：每次在getView()方法 中会调用View的findViewById()方法来获取一次控件的实例；借助ViewHolder可以减少findViewById的次数。
 * 
 */
	
	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		Fruit fruit = getItem(position);// 获取当前项的Fruit实例
		View view;//这里只是声明了view，并没有对其初始化
		ViewHolder viewHolder ;//这里只是声明了viewHolder，并没有对其初始化
		if (convertView == null) {
			view = LayoutInflater.from(getContext()).inflate(resourceId, null);
			viewHolder = new ViewHolder();
			viewHolder.fruitImage= (ImageView) view.findViewById(R.id.fruit_image);
			viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
			view.setTag(viewHolder);//将ViewHolder存储在View中；在此存储的目的是为了convertView不为空的时候调用View的getTag()方法，把ViewHolder重新取出。
		} else {
			view = convertView;//重用为空时候加载的布局，并初始化view
			viewHolder=(ViewHolder) view.getTag();
		}
		viewHolder.fruitImage.setImageResource(fruit.getImageId());// 设置显示的图片
		viewHolder.fruitName.setText(fruit.getName());// 设置显示的文字
		return view;

	}
	class ViewHolder{
		ImageView fruitImage;
		TextView fruitName;
	}

}

4.MainActivity.java

package com.zhc.listviewtest;

import java.util.ArrayList;
import java.util.List;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
import android.widget.Toast;
import android.app.Activity;

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);
		//1.初始化水果数据
		initFruits();
		
		//2.提供一个自己定制的Adapter（跟android提供的适配器ArrayAdapter的原理是一样的）
		FruitAdappter adapter = new FruitAdappter(MainActivity.this, R.layout.fruit_item, fruitList);//重写构造方法
		
		//3.找到ListView控件
		ListView listView = (ListView) findViewById(R.id.list_view);
		
		//4.给ListView设置适配器
		listView.setAdapter(adapter);
		
		//5.LiistView的点击事件
		listView.setOnItemClickListener(new OnItemClickListener() {

			@Override
			public void onItemClick(AdapterView<?> parent, View view, int position,
					long id) {
				Fruit fruit = fruitList.get(position);
				Toast.makeText(MainActivity.this, fruit.getName(), Toast.LENGTH_SHORT).show();
			}
		});
		
	}
	private void initFruits() {
		Fruit apple=new Fruit("Apple",R.drawable.ic_launcher);
		fruitList.add(apple);
		Fruit banana=new Fruit("Banana",R.drawable.ic_launcher);
		fruitList.add(banana);
		Fruit orange=new Fruit("Orange",R.drawable.ic_launcher);
		fruitList.add(orange);
		Fruit watermelon=new Fruit("Watermelon",R.drawable.ic_launcher);
		fruitList.add(watermelon);
		Fruit pear=new Fruit("Pear",R.drawable.ic_launcher);
		fruitList.add(pear);
		Fruit grape=new Fruit("Grape",R.drawable.ic_launcher);
		fruitList.add(grape);
		Fruit pineapple=new Fruit("Pineapple",R.drawable.ic_launcher);
		fruitList.add(pineapple);
		Fruit strawberry=new Fruit("Strawberry",R.drawable.ic_launcher);
		fruitList.add(strawberry);
		Fruit cherry=new Fruit("Cherry",R.drawable.ic_launcher);
		fruitList.add(cherry);
		Fruit mango=new Fruit("Mango",R.drawable.ic_launcher);
		fruitList.add(mango);
		Fruit mango1=new Fruit("Mango1",R.drawable.ic_launcher);
		fruitList.add(mango1);
		Fruit mango2=new Fruit("Mango2",R.drawable.ic_launcher);
		fruitList.add(mango2);
		Fruit mango3=new Fruit("Mango3",R.drawable.ic_launcher);
		fruitList.add(mango3);
		Fruit mango4=new Fruit("Mango4",R.drawable.ic_launcher);
		fruitList.add(mango4);
	}
}

5.activity_main.java

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    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"
        />

</RelativeLayout>

二、运行结果