关于android:Android-开发入门ListView-的用法

3.5.1 ListView 的简略用法

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    # 退出一个占满屏幕的 ListView
    <ListView
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
    </ListView>

</LinearLayout>

public class MainActivity extends AppCompatActivity {private String[] data = {"Apple", "Banana", ...};

    @Override
    protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        // 构建适配器，simple_list_item_1 是安卓内置的布局文件
        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);
    }

3.5.2 定制 ListView 的界面

# app/src/main/java/com/example/listviewtest/Fruit.java

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;}

}

# app/src/main/res/layout/fruit_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    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"   # 垂直居中
        android:layout_marginLeft="10dp" />

</LinearLayout>

创立自定义的适配器，继承于 ArrayAdapter：

# app/src/main/java/com/example/listviewtest/FruitAdapter.java

public class FruitAdapter extends ArrayAdapter<Fruit> {

    private int resourceId;

    public FruitAdapter(Context context, int textViewResourceId,
                        List<Fruit> objects) {super(context, textViewResourceId, objects);
        resourceId = textViewResourceId;
    }

    // 在每个子项被滚动到屏幕内会被调用
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // 获取以后项的 Fruit 实例
        Fruit fruit = getItem(position);
        View view = LayoutInflater.from(getContext()).inflate(resourceId, 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;
    }
}

public class MainActivity extends AppCompatActivity {private List<Fruit> fruitList = new ArrayList<Fruit>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits(); // 初始化水果数据
        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("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);
        }
    }
}

3.5.3 晋升 ListView 的运行效率

public class FruitAdapter extends ArrayAdapter<Fruit> {

    ...
    
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {Fruit fruit = getItem(position); // 获取以后项的 Fruit 实例
        View view;
        ViewHolder viewHolder;
        // convertView 用于将之前加载好的布局进行缓存
        if (convertView == null) {view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.fruitImage = (ImageView) view.findViewById (R.id.fruit_image);
            viewHolder.fruitName = (TextView) view.findViewById (R.id.fruit_name);
            // 将 ViewHolder 存储在 View 中
            view.setTag(viewHolder);
        } else {
            view = convertView;
            // 从新获取 ViewHolder
            viewHolder = (ViewHolder) view.getTag();}
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());
        return view;
    }

    // 外部类，用于对控件的实例进行缓存
    class ViewHolder {
        ImageView fruitImage;
        TextView fruitName;
    }
}

3.5.4 ListView 的点击事件

    @Override
    protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // 初始化水果数据
        initFruits();
        FruitAdapter adapter = new FruitAdapter(MainActivity.this, R.layout.fruit_item, fruitList);
        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
        // 绑定子项的事件监听
        listView.setOnItemClickListener(new AdapterView.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();}
        });
    }