ListView

[ ListView 控件]

< ListView的简单用法 >

MainActivity.java

    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        //ArrayAdapter<>（ 当前上下文， ListView 子项布局的id， 适配的数据 ）        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);    }

< 定制 ListView 界面 >

Fruit.java（ ListView 子项定义为一个类）

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 name;    }    public int getImageId() { return imageId; }}

FruitAdapter.java（自定义的 Adapter）

public class FruitAdapter extends ArrayAdapter<Fruit> {    private int resourceId;    // 重写构造方法，将 上下文，ListView 子项布局的id，数据。都传进来    public FruitAdapter(Context context, int textViewResourceId, List<Fruit> objects) {        super(context, textViewResourceId, objects);        resourceId = textViewResourceId;    }    // 这个方法在每个子项被滚到屏幕的时候调用    @Override    public View getView(int position, View convertView, ViewGroup parent){        // getItem() 方法获取当前的实例        Fruit fruit = getItem(position);        //LayoutInflater() 为这个子项加载我们传入的布局        View view = LayoutInflater.from(getContext()).inflate(resourceId, null);        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;    }}

MainActivity.java

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);        //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);    }    private void initFruits() {        Fruit apple = new Fruit("Apple", R.drawable.apple_pic);        fruitList.add(apple);    }}

fruit_item.xml

<?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="50dp">    <ImageView        android:id="@+id/fruit_image"        android:layout_width="50dp"        android:layout_height="50dp" />    <TextView        android:id="@+id/fruit_name"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center"        android:layout_marginLeft="10dp"        android:textSize="20dp"/></LinearLayout>

< 提升 LisstView 的运行效率 >

• 自定义的 Adapter 中 getView() 方法的 convertView 参数是将之前加载好的布局进行缓存
• 创建 ViewHolder 内部类，将通过 findViewById() 获取的控件存放进去。这样就不需要次次用 findViewById 来获取

public class FruitAdapter extends ArrayAdapter<Fruit> {    private int resourceId;    ...    // 这个方法在每个子项被滚到屏幕的时候调用    @Override    public View getView(int position, View convertView, ViewGroup parent){        ...        //LayoutInflater() 为这个子项加载我们传入的布局//          View view = LayoutInflater.from(getContext()).inflate(resourceId, null);        View view;        ViewHolder viewHolder;        if(convertView == null){            view = LayoutInflater.from(getContext()).inflate(resourceId, null);            viewHolder = new ViewHolder();            viewHolder.fruitImage = (ImageView) view.findViewById(R.id.fruit_image);            viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);            view.setTag(viewHolder); //将 ViewHolder 存储在 View 中        }else{            view = convertView;            // getTag() 方法将 ViewHolder 重新取出            viewHolder = (ViewHolder) view.getTag();         }//        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());        viewHolder.fruitImage.setImageResource(fruit.getImageId());        viewHolder.fruitName.setText(fruit.getName());        return view;    }    //将所有控件实例都放在 ViewHolder 中，而不要次次通过 findViewById() 来获取实例控件了    class ViewHolder{        ImageView fruitImage;        TextView fruitName;    }}

< LisstView 的点击事件 >

• 运用 setOnItemClickListener() 方法来为 ListView 注册一个监听器
• 用户点击 ListView 任何子项都会回调 onItemClick() 方法
• 通过 position 参数判断用户点击的是哪一个子项

        listView.setOnItemClickListener(new 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();            }        });