Android RecycleView

用法

导入依赖库

implementation 'androidx.recyclerview:recyclerview:1.0.0'

主布局添加控件

<?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">
    
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

</LinearLayout>

子布局 fruit_item.xml

<?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="wrap_content"
    android:orientation="horizontal">

    <ImageView
        android:id="@+id/fruit_image"
        android:layout_width="32dp"
        android:layout_height="32dp" />

    <TextView
        android:id="@+id/fruit_name"
        android:layout_width="wrap_content"
        android:layout_height="32dp"
        android:layout_marginLeft="10dp" />

</LinearLayout>

实体类 Fruit

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;
    }
}

新建类FruitAdapter继承自RecyclerView.Adapter，指定泛型为FruitAdapter.ViewHolder(在该adapter中新建ViewHolder类继承自RecyclerView.ViewHolder)

• 首先定义了内部类 ViewHolder，继承自RecyclerView.ViewHolder，其中传入了一个itemView参数，这个参数继承通常是RecycleView子项的最外层布局，通过它就能取到 ImageView 和 TextView 了
• 必须重写的三个方法
  • onCreateViewHolder()： 用来创建ViewHolder实例，在这个方法中，将 子布局 传入创建的ViewHolder实例，然后将其返回
  • onBindViewHolder()：对RecyclerView子项数据赋值，会在子项布局滚动到屏幕时执行
  • getItemCount()：返回数据源的长度，用来判断子布局的个数

public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {

    private List<Fruit> mFruitList; //需要传入一个数据集合来构建adapter

    public FruitAdapter(List<Fruit> mFruitList) {
        this.mFruitList = mFruitList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false); //传入子项布局 fruit_item 构建view 进而构建viewholder
        ViewHolder viewHolder = new ViewHolder(view);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Fruit fruit = mFruitList.get(position);
        holder.fruitImage.setImageResource(fruit.getImageId());
        holder.fruitName.setText(fruit.getName());
    }

    @Override
    public int getItemCount() {
        return mFruitList.size(); //list.size()直接得到数量
    }

    static class ViewHolder extends RecyclerView.ViewHolder {
        ImageView fruitImage;
        TextView fruitName;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            fruitImage = (ImageView) itemView.findViewById(R.id.fruit_image);
            fruitName = (TextView) itemView.findViewById(R.id.fruit_name);
        }
    }
}

主活动修改

• 先通过initFruit()初始化水果数据，接着创建RecycleView实例，然后创建了一个LinearLayoutManger对象，并将它设置到RecycleView中，表示使用线性布局，最后创建FruitAdapter实例建立数据关联

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(fruitList);
        RecyclerView recyclerView = findViewById(R.id.recycler_view);
        
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        //记住 recyclerView需要设置两个东西，一个是布局，一个是adapter
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setAdapter(adapter);
    }

    private void initFruits(){
        for (int i = 0; i < 2; i++){
            Fruit apple = new Fruit("苹果", R.drawable.apple);
            fruitList.add(apple);
            Fruit banana = new Fruit("香蕉", R.drawable.banana);
            fruitList.add(banana);
            Fruit orange = new Fruit("橙子", R.drawable.orange);
            fruitList.add(orange);
            Fruit watermelon = new Fruit("西瓜", R.drawable.watermelon);
            fruitList.add(watermelon);
            Fruit pear = new Fruit("梨", R.drawable.pear);
            fruitList.add(pear);
            Fruit grape = new Fruit("葡萄", R.drawable.grape);
            fruitList.add(grape);
            Fruit pineapple = new Fruit("菠萝", R.drawable.pineapple);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit("草莓", R.drawable.strawberry);
            fruitList.add(strawberry);
            Fruit cherry = new Fruit("樱桃", R.drawable.cherry);
            fruitList.add(cherry);
            Fruit mango = new Fruit("芒果", R.drawable.mango);
            fruitList.add(mango);
        }
    }
}

横向滚动

只修改调用的LineatLayout属性，修改为水平，加入一行代码即可

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    initFruits();
    FruitAdapter adapter = new FruitAdapter(fruitList);
    RecyclerView recyclerView = findViewById(R.id.recycler_view);

    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);  //这里修改为水平
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setAdapter(adapter);
}

瀑布流效果

使用StaggeredGridLayoutManger布局，仅修改一行代码：

• StaggeredGridLayoutManger的构造函数接收两个参数，第一个参数用来指定布局列数；第二个参数指定排列方向

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    initFruits();
    FruitAdapter adapter = new FruitAdapter(fruitList);
    RecyclerView recyclerView = findViewById(R.id.recycler_view);

    StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setAdapter(adapter);
}

点击事件简单实现

• 多种方式，可在onBindViewHolder()中实现

  @Override
     public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
         final Fruit fruit = mFruitList.get(position);
         holder.fruitImage.setImageResource(fruit.getImageId());
         holder.fruitName.setText(fruit.getName());
         holder.fruitImage.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View v) {
                 Log.d("tag",fruit.getName());
             }
         });
     }