ListView初探

ListView简介:
ListView是Android中最常用的控件之一,比如刷微博,联系人列表,等。以垂直的列表形式显示列表项。下面是<<第一行代码>>书中的例子。摘取出来以供分享.
ListView的简单用法:
修改xml中的代码如下:

<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"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context=".MainActivity" >    <ListView         android:id="@+id/list_view"        android:layout_height="match_parent"        android:layout_width="match_parent"        ></ListView></RelativeLayout>

在布局中加入了ListView控件,宽高都是match_parent。
接下来修改MainActivity：

public class MainActivity extends Activity {            private String[] data={"Apple","Banana","Orange","Watermelon","Pear","Grape","LAIZZ","FSDFF","FSDF"};    @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);    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.main, menu);        return true;    }}

数据中的数据无法直接传递给ListView，需借助适配器来完成。其中一个就是ArrayAdapter,它可以通过泛型来指定适配的数据类型,然后在构造函数中传入数据。最后调用setAdapter()方法将适配器对象传进去.运行程序如图：

定制ListView的界面:
为了显示更加丰富的内容,我们现在对其进行定制.
首先准备一组图片，分别对应每一种水果。然后对其进行描述.
新建类Fruit,:

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

然后为ListView的子项指定一个布局。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="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>

定义一个ImageView显示水果图片,又定义一个TextView显示水果名称.
接下来创建一个自定义适配器,这个适配器继承自ArrayAdapter，并将泛型指定为Fruit类。新建类FruitAdapter：

public class FruitAdapter extends ArrayAdapter<Fruit> {    public FruitAdapter(Context context, int resource, List<Fruit> objects) {        super(context, resource, objects);        // TODO 自动生成的构造函数存根    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {        // TODO 自动生成的方法存根        Fruit fruit=getItem(position);        View view=LayoutInflater.from(getContext()).inflate(R.layout.fruit_item, null);        ImageView fruitimage=(ImageView)view.findViewById(R.id.fruit_image);        TextView fruitname=(TextView)view.findViewById(R.id.fruit_name);        fruitimage.setImageResource(fruit.getimage());        fruitname.setText(fruit.getname());        return view;    }}

FruitAdapter重写父类的一组构造函数,用于将上下文,ListView子项布局的ID和数据传递进来.另外重写了getView()方法,这个方法在每个子项滚动到屏幕的时候调用。
下面修改MainActivity中的代码:

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() {        // TODO 自动生成的方法存根        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.apple_pic);        fruitList.add(orange);        Fruit watermelon=new Fruit("Watermelon", R.drawable.banana_pic);        fruitList.add(watermelon);        Fruit pear=new Fruit("Pear", R.drawable.apple_pic);        fruitList.add(pear);        Fruit Grape=new Fruit("Grape", R.drawable.banana_pic);        fruitList.add(Grape);        Fruit Cheery=new Fruit("Cheery", R.drawable.apple_pic);        fruitList.add(Cheery);        Fruit Mango=new Fruit("Mango", R.drawable.banana_pic);        fruitList.add(Mango);    }

运行效果如图：