Android —定制ListView

ListView

Android 第一行代码 第二版 第三章ListView
- activity_main.xml文件中写入listView

<?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">    <ListView        android:id="@+id/list_view"        android:layout_width="match_parent"        android:layout_height="wrap_content">    </ListView></LinearLayout>

• 定义一个实体类Fruit

public class Fruit {    private String name;    //水果名称    private int imageId;    //图像id    public Fruit(String name, int imageId) {        this.name = name;        this.imageId = imageId;    }    public String getName() {        return name;    }    public void setImageId(int imageId) {        this.imageId = imageId;    }}

• 指定子项的自定义布局fruit_item

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent">    <ImageView        android:id="@+id/image"        android:layout_width="wrap_content"        android:layout_height="wrap_content" />    <TextView        android:id="@+id/text"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_vertical"        android:layout_marginLeft="10dp"/>    <!--文字水平方向上居中显示，距离左侧10dp--></LinearLayout>

• 自定义适配器FruitAdapter继承自ArrayAdapter
  
  1. 重写构造函数，分别传递上下文，子项布局id和数据
  2. 重写getView()方法
  3. 利用convertView来提升运行效率
  4. 创建ViewHolder类，优化findViewByID()
  5. 利用getTag(),setTag()保存ViewHolder

public class FruitAdapter extends ArrayAdapter<Fruit> {    private int resourceId;    //1.构造函数重写    public FruitAdapter(Context context, int resource, List<Fruit> objects) {        super(context, resource, objects);        //上下文，子项布局id，数据        resourceId = resource;    }    //ctrl + O重写getView方法，每个子项被滚动到屏幕内调用    //position第几个子项,convertView将之前加载好的布局进行缓存    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {        View view;        Fruit fruit = getItem(position);    // 获取到当前Fruit实例        ViewHolder viewHolder;        //优化listView的运行效率        if(convertView !=null){            view = convertView;            viewHolder = (ViewHolder) view.getTag();        } else {            //resourceId将要加载的layout布局文件；parent层次结构的父类;false标准写法            view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);            viewHolder = new ViewHolder();            viewHolder.imageView = (ImageView) view.findViewById(R.id.image);            viewHolder.textView = (TextView) view.findViewById(R.id.text);            view.setTag(viewHolder);    //将viewHolder保存到view中        }        viewHolder.imageView.setImageResource(fruit.getImageId());     //设置image图像        viewHolder.textView.setText(fruit.getName());        return view;    }    class ViewHolder{        ImageView imageView;        TextView textView;    }}

• 修改MainActivity中的方法
  
  1. 初始化adapter
  2. 获取listView
  3. 装载adapter
  4. 设置item点击事件

public class MainActivity extends AppCompatActivity {    private List<Fruit> fruitList = new ArrayList<>();    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        //隐藏标题栏        ActionBar actionBar = getSupportActionBar();        if(actionBar!=null) {            actionBar.hide();        }        initFruit();    // 初始化fruitList        //1.初始化adpater        FruitAdapter fruitAdapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,                fruitList);        //2.获取listView        ListView listView = (ListView) findViewById(R.id.list_view);        //3.装载adapter        listView.setAdapter(fruitAdapter);        //设置item项点击事件        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_LONG).show();            }        });    }    private void initFruit() {        //利用循环将数据传入2次，以实现ListView将屏幕充满        for( int i = 0 ; i < 2 ; i++){            Fruit apple = new Fruit("apple",R.drawable.apple_pic);  //利用构造函数定义apple对象            fruitList.add(apple);   //装载apple到fruitList            Fruit banana = new Fruit("banana",R.drawable.banana_pic);            fruitList.add(banana);            Fruit cherry = new Fruit("cherry",R.drawable.cherry_pic);            fruitList.add(cherry);            Fruit grape = new Fruit("grape",R.drawable.grape_pic);            fruitList.add(grape);            Fruit mango = new Fruit("mango",R.drawable.mango_pic);            fruitList.add(mango);            Fruit orange = new Fruit("orange",R.drawable.orange_pic);            fruitList.add(orange);            Fruit pear = new Fruit("pear",R.drawable.pear_pic);            fruitList.add(pear);            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 watermelon = new Fruit("watermelon",R.drawable.watermelon_pic);            fruitList.add(watermelon);        }    }}