Android第一行代码(第二版)

3.5最常用和最难用的控件----ListViewListView非常常见，也是Android中最常见的空间之一，几乎所有程序都会用到，QQ聊天，刷微博，诸如此类。ListView用法也是比较复杂。下面以一个小项目来练习ListView。新建一个ListViewTest项目，默认设置。

public class MainActivity extends AppCompatActivity {    private String[] data = {"Apple","Banana","Orange","Watermelon",            "Pear","Grape","Pineapple","Strawberry","Cherry","Mango",            "Apple","Banana","Orange","Pineapple","Strawberry","Cherry","Mango",            "Apple","Banana","Orange"};    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        ArrayAdapter adapter = new ArrayAdapter(                MainActivity.this,android.R.layout.simple_list_item_1,data);        ListView listView = (ListView) findViewById(R.id.list_view);        listView.setAdapter(adapter);    }}

如图所示，先提供好数据，String类型的数组数据，数组中的数据无法直接传递给ListView的，要借助适配器来完成。这里用ArrayAdapter。它可通过泛型来指定要适配的实现类，然后在构造函数中把适配的数据传入。ArrayAdapter有多个构造函数重载，这里把ArrayAdapter泛型指定为String，再在ArrayAdapter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。使用了android.R.layout.simple_list_item_1作为ListView的子项布局id，这是Android内部的布局文件，里面只有一个TextView，可用于简单显示一段文本。这样适配器对象就构建好了。3.5.2定制ListView界面准备好图片，对应上面提供的每一种水果。让水果名称的旁边都有一个图样。定义一个实体类，作为List适配器的适配类型。新建Fruit类，代码如下：

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;    }}

然后为了ListView的子项指定一个自定义的布局，新建fruit_item.xml，

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"     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_vertical"        android:layout_marginLeft="10dp"/>LinearLayout>

创建一个自定义适配器，继承自ArrayAdapter，将泛型指定为Fruit类。新建类FruitAdapter。

public class FruitAdapter extends ArrayAdapter {    private int resourcedId;    public FruitAdapter(Context context, int textViewResourceId, List objects) {        super(context,textViewResourceId,objects);        resourcedId = textViewResourceId;    }    @NonNull    @Override    public View getView(int position, @Nullable View convertView,  ViewGroup parent) {        Fruit fruit = getItem(position);        View view = LayoutInflater.from(getContext()).inflate(resourcedId,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;    }}

修改MainActivity代码：

public class MainActivity extends AppCompatActivity {   private List fruitList = new ArrayList<>();    @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() {        for (int i = 0;i<2;i++) {            Fruit apple = new Fruit("Apple",R.drawable.apple_pic);            fruitList.add(apple);            Fruit banana = new Fruit("Apple",R.drawable.banana_pic);            fruitList.add(banana);            Fruit orange = new Fruit("Apple",R.drawable.orange_pic);            fruitList.add(orange);            Fruit watermelon = new Fruit("Apple",R.drawable.watermelon_pic);            fruitList.add(watermelon);            Fruit pear = new Fruit("Apple",R.drawable.pear_pic);            fruitList.add(pear);            Fruit grape = new Fruit("Apple",R.drawable.grape_pic);            fruitList.add(grape);            Fruit pineapple = new Fruit("Apple",R.drawable.pineapple_pic);            fruitList.add(pineapple);            Fruit strawberry = new Fruit("Apple",R.drawable.strawberry_pic);            fruitList.add(strawberry);            Fruit cherry = new Fruit("Apple",R.drawable.cherry_pic);            fruitList.add(cherry);            Fruit mango = new Fruit("Apple",R.drawable.mango_pic);            fruitList.add(mango);        }    }}

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