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;
      }
      ...
  }
  

  这是我学习Android的笔记,参考书<<第一行代码-第二版>>,感谢郭霖大神
  如有不足之处,可以一起讨论
  附上郭霖的blog http://blog.csdn.net/guolin_blog