更加强大的滚动控件 RecyclerView #P123

基本用法

  • 需要在build.gradle添加依赖库 recyclerview
  • activity_main.xml文件添加RecyclerView
  • 图片,Furit类,fruit_item.xml
  • 新建FruitAdapter类,作为适配器,继承自RecyclerView.Adapter ,并且泛型指定为FruitAdapter.ViewHolder ViewHolder是内部类 
<android.support.v7.widget.RecyclerView
  android:id="@+id/recycler_view"
  android:layout_width="match_parent"
  android:layout_height="match_parent" />

###新建FruitAdapter

  1. 定义内部类ViewHoler ,继承自RecyclerView.ViewHolder
  2. ViewHoler的构造函数传入一个View参数,这个参数通常就是RecyclerView子项的最外层布局,通过findViewById() 方法来获取布局中的Imageiew和TextView的实例
  3. FruitAdapter 中也有构造函数,这个方法用于把要展示的数据源传进来,并赋值给一个全部变量mFruitList
  4. FruitAdapter继承自RecyclerView.Adapter,所以要重写onCreatViewHolder(),onBingViewHolder(),getItemCount()
  1. onCreatViewHolder()用来创建ViewHolder实例,将fruit_item布局加载进来,然后创建一个ViewHoler实例,并把加载出来的布局传入构造函数中,最后将ViewHoler的实例返回
  2. onBingViewHolder()用于对RecyclerView子项的数据进行赋值,会在每个子项被滚动到屏幕内的时候执行,通过position 参数得到当前项的Fruit实例,然后将数据设置到ViewHolder的ImageView和TextView当中即可
  3. getItemCount() 告诉RecyclerView有多少子项 ,返回 mFruitList.size()
public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {
  private List<Fruit> mFruitList;

  /**
   * Created by Mason on 2017/11/16.
   */

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

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

  public FruitAdapter(List<Fruit> fruitList) {

      mFruitList = fruitList;
  }

  @Override
  public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
      View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);
      ViewHolder holder = new ViewHolder(view);
      return holder;
  }

  @Override
  public void onBindViewHolder(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();
  }
}

改变为横向RecyclerView

  • fruit_item.xml 的LinearLayout布局改为orientation:"vertical" 垂直布局 ,默认horizontal水平布局
  • 修改TextView和ImageView的layout_gravity 修改成水平居中center_horizontal
  • MainActivity.java文件 调用LinearLayoutManager的setOrientation()方法设置布局排列方向 添加layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL)
  • xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="100dp"
android:layout_height="wrap_content" >

<ImageView
    android:id="@+id/fruit_image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal" />

<TextView
    android:id="@+id/fruit_name"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:layout_marginTop="10dp" />
</LinearLayout>
  • MainActivity.java
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    intiFruits();
    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
    recyclerView.setLayoutManager(layoutManager);
    FruitAdapter adapter = new FruitAdapter(fruitList);
    recyclerView.setAdapter(adapter);
}

RecyclerView 点击事件

  • 需要自己给子项具体的View注册点击事件
  • 虽然比ListView繁琐,但是ListView给单独按钮注册事件更加繁琐
  1. 修改ViewHolder,添加fruitView变量来保存子项最外层布局的实例
  2. 然后在onCreatViewHolder()方法中注册点击事件就行了.
  3. 这里项目分别为最外层布局和Image注册了点击事件.
  • RecyclerView强大在于,可以轻松实现子项中任意控件或布局的点击事件
  1. 我们先获取用户点击的position
  2. 通过position拿到相应的Fruit实例
  3. 再使用Toast弹出两种不同的内容
public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {
    private List<Fruit> mFruitList;

    /**
     * Created by Mason on 2017/11/16.
     */

    static class ViewHolder extends RecyclerView.ViewHolder {
        View fruitView;  // 添加
        ImageView fruitImage;
        TextView fruitName;

        public ViewHolder(View view) {
            super(view);
            fruitView = view;  //添加
            fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
            fruitName = (TextView) view.findViewById(R.id.fruit_name);
        }
    }

    public FruitAdapter(List<Fruit> fruitList) {

        mFruitList = fruitList;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);
        final ViewHolder holder = new ViewHolder(view);  // 添加
        holder.fruitView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(v.getContext(), "you click view   " + fruit.getName(), Toast.LENGTH_SHORT).show();
            }
        });
        holder.fruitImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(v.getContext(), "you click image   " + fruit.getName(), Toast.LENGTH_SHORT).show();
            }
        });
        return holder;
    }
    ...
}