ListView

简单使用

1.在界面编写ListView

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

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

</LinearLayout>

2.实例化一个ArrayAdapter对象，填入Context上下文，每一项的布局文件，数据这三个参数

 private final String[] data = {
            "Apple", "Banana", "Orange", "Pear", "Mango", "Grape",
            "watermelon", "Cherry", "Pineapple", "Strawberry",

            "Apple", "Banana", "Orange", "Pear", "Mango", "Grape",
            "watermelon", "Cherry", "Pineapple", "Strawberry"
    };
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1,data);

3.ListView填装适配器

ListView listView = findViewById(R.id.listView);
listView.setAdapter(adapter);

丰富你的ListView

1.只显示一段文本实在是太单调了，我们现在对ListView的界面进行定制，先创建一个实体类，作为适配器的适配类型

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;
    }
}

2.然后定义ListView子项的布局

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

    <ImageView
        android:id="@+id/fruit_image"
        android:layout_width="45dp"
        android:layout_height="45dp" />

    <TextView
        android:id="@+id/fruit_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="10dp"
        android:layout_gravity="center_vertical"/>
    
</LinearLayout>

3.接下来创建一个自定义的适配器，这个适配器经过优化处理了。

public class FruitAdapter extends ArrayAdapter<Fruit> {

    private int resourceId;

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


    // getView()会在每个子项滚动到屏幕内的时候调用
    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        // 通过getItem()得到当前项的Fruit实例
        Fruit fruit = getItem(position);

        View view;

        // ViewHolder 是用来储存ListView子项的各种控件
        ViewHolder viewHolder;  

        // 提升ListView的运行效率
        if (convertView == null) {
            // 使用LayoutInflater，来为这个子项加载我们传入的布局
            view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);

            viewHolder = new ViewHolder();
            viewHolder.fruitImage = view.findViewById(R.id.fruit_image);
            viewHolder.fruitName = 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;
    }
}

4.最后按照简单使用的三步骤

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

private void onCreate(Bundle savedInstanceState)  {
...
 // 初始化数据，完成数据的填充
 for (int i = 0; i < data.length; i++) {
            Fruit fruit = new Fruit(data[i], R.mipmap.ic_launcher);
            fruitList.add(fruit);
        }

 ListView listView = findViewById(R.id.listView);
 FruitAdapter adapter = new FruitAdapter(this, R.layout.fruit_item, fruitList);
 listView.setAdapter(adapter);
}

ListView点击事件

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                Fruit fruit = fruitList.get(i);
                Toast.makeText(MainActivity.this, fruit.getName(), Toast.LENGTH_LONG).show();
            }
        });