更加強(qiáng)大的滾動控件 RecyclerView #P123

基本用法

• 需要在build.gradle添加依賴庫 recyclerview
• activity_main.xml文件添加RecyclerView
• 圖片,Furit類,fruit_item.xml
• 新建FruitAdapter類,作為適配器,繼承自RecyclerView.Adapter ,并且泛型指定為FruitAdapter.ViewHolder ViewHolder是內(nèi)部類

  <android.support.v7.widget.RecyclerView
    android:id="@+id/recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />
  

新建FruitAdapter

1. 定義內(nèi)部類ViewHoler ,繼承自RecyclerView.ViewHolder
2. ViewHoler的構(gòu)造函數(shù)傳入一個View參數(shù),這個參數(shù)通常就是RecyclerView子項的最外層布局,通過findViewById() 方法來獲取布局中的Imageiew和TextView的實例
3. FruitAdapter 中也有構(gòu)造函數(shù),這個方法用于把要展示的數(shù)據(jù)源傳進(jìn)來,并賦值給一個全部變量mFruitList
4. FruitAdapter繼承自RecyclerView.Adapter,所以要重寫onCreatViewHolder(),onBingViewHolder(),getItemCount()
   1. onCreatViewHolder()用來創(chuàng)建ViewHolder實例,將fruit_item布局加載進(jìn)來,然后創(chuàng)建一個ViewHoler實例,并把加載出來的布局傳入構(gòu)造函數(shù)中,最后將ViewHoler的實例返回
   2. onBingViewHolder()用于對RecyclerView子項的數(shù)據(jù)進(jìn)行賦值,會在每個子項被滾動到屏幕內(nèi)的時候執(zhí)行,通過position 參數(shù)得到當(dāng)前項的Fruit實例,然后將數(shù)據(jù)設(shè)置到ViewHolder的ImageView和TextView當(dāng)中即可
   3. getItemCount() 告訴RecyclerView有多少子項 ,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();
     }
   }
   

改變?yōu)闄M向RecyclerView

• fruit_item.xml 的LinearLayout布局改為orientation:"vertical" 垂直布局 ,默認(rèn)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 調(diào)用LinearLayoutManager的setOrientation()方法設(shè)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 點擊事件

• 需要自己給子項具體的View注冊點擊事件
• 雖然比ListView繁瑣,但是ListView給單獨按鈕注冊事件更加繁瑣
  1. 修改ViewHolder,添加fruitView變量來保存子項最外層布局的實例
  2. 然后在onCreatViewHolder()方法中注冊點擊事件就行了.
  3. 這里項目分別為最外層布局和Image注冊了點擊事件.
• RecyclerView強(qiáng)大在于,可以輕松實現(xiàn)子項中任意控件或布局的點擊事件
  1. 我們先獲取用戶點擊的position
  2. 通過position拿到相應(yīng)的Fruit實例
  3. 再使用Toast彈出兩種不同的內(nèi)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;
      }
      ...
  }
  

  這是我學(xué)習(xí)Android的筆記,參考書<<第一行代碼-第二版>>,感謝郭霖大神
  如有不足之處,可以一起討論
  附上郭霖的blog http://blog.csdn.net/guolin_blog