ListView详解

Posted 2021-02-05 kyun

ListView 基本使用

ListView是android最常用的控件之一，允许用户通过手指上下滑动的方式将屏幕外的数据滚动到屏幕内。ListView通过Adapter加载数据到屏幕上。

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

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

</LinearLayout>

 

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private List<Fruit> fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);
        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
        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();
            }
        });
    }

    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 watermelon = new Fruit("Watermelon",R.drawable.watermelon_pic);
            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 strawberry = new Fruit("Strawberry",R.drawable.strawberry_pic);
            fruitList.add(strawberry);
            Fruit mango = new Fruit("Mango",R.drawable.mango_pic);
            fruitList.add(mango);
        }
    }
}

FruitAdapter.java  在getView方法中进行了ListView运行效率优化

public class FruitAdapter extends ArrayAdapter<Fruit> {

    private int resourceId;

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

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Fruit fruit = getItem(position);
        View view;
        ViewHolder viewHolder;
        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);
            view.setTag(viewHolder);
        } else {
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        }
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());
        return view;
    }

    class ViewHolder {
        ImageView fruitImage;
        TextView fruitName;
    }
}

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;
    }
}