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

ListView中的每一列的View。

填入View的数据或者图片等。

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();

}

});