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.javapublic 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.javapublic 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(); } }); }