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();}
});
}