安卓控件RecyclerVieW

  RecyclerView是官方在5.0之后新添加的控件，推出用来替代ListView和GridView的列表控件。为了保证RecyclerView在所有Android系统版本上都能使用。Google将RecyclerView控件定义在了AndroidX中，只需要在项目的build.gradle中添加RecyclerView库的依赖，就能保证在所有Android系统版本上都可以使用RecyclerView控件了。RecyclerView会回收视图重复利用。当列表滚动展示区域之外（宽度或高度超出父容器）时，RecyclerView不会销毁视图，而是将视图置于列表滑动方向准备显示的那端。这种渲染方式可以显著提高性能。

导入依赖

  file→Project Structure…→Dependencies→ app→ + → Library Dependency。

  输入androidx.recyclerview，然后点击Search。

简单使用

  修改activity_main.xml中的代码。在布局中加入RecyclerView控件也是非常简单的，先为RecyclerView指定一个id，然后将宽度和高度都设置为match_parent，这样RecyclerView就占满了整个布局的空间。需要注意的是，由于RecyclerView并不是内置在系统SDK当中的，所以需要把完整的包路径写出来。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>
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  自定义布局fruit_item.xml。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="60dp">
    <ImageView
        android:id="@+id/fruitImage"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"/>
    <TextView
        android:id="@+id/fruitName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp" />
</LinearLayout>
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  编写Fruit类。

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;
    }
}
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  创建一个继承自ArrayAdapter的自定义适配器FruitAdapter。

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

    private List<Fruit> mFruitList;

    static class ViewHolder extends RecyclerView.ViewHolder{
        ImageView fruitImage;
        TextView fruitName;
        public ViewHolder(View view){
            super(view);
            fruitImage = (ImageView)  view.findViewById(R.id.fruitImage);
            fruitName = (TextView) view.findViewById(R.id.fruitName);
        }
    }
    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();
    }
}
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  最后修改MainActivity中的代码。

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(); // 初始化数据
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter adapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);
    }
    private void initFruits(){
        for(int i = 0; i < 2; i++){
            Fruit apple = new Fruit("Apple", R.mipmap.ic_launcher);
            fruitList.add(apple);
            Fruit banana = new Fruit("banana", R.mipmap.ic_launcher);
            fruitList.add(banana);
            Fruit orange = new Fruit("orange", R.mipmap.ic_launcher);
            fruitList.add(orange);
            Fruit waternelon = new Fruit("waternelon", R.mipmap.ic_launcher);
            fruitList.add(waternelon);
            Fruit pear = new Fruit("pear", R.mipmap.ic_launcher);
            fruitList.add(pear);
            Fruit grape = new Fruit("grape", R.mipmap.ic_launcher);
            fruitList.add(grape);
            Fruit pineapple = new Fruit("pineapple", R.mipmap.ic_launcher);
            fruitList.add(pineapple);
        }
    }
}
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实现横向滚动

  修改自定义布局fruit_item.xml。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     <!--修改部分-->
    android:orientation="vertical"
    android:layout_width="80dp"
    android:layout_height="match_parent">
   <!--修改部分-->
    <ImageView
        android:id="@+id/fruitImage"
        android:layout_width="40dp"
        android:layout_height="40dp"
        <!--修改部分-->
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="10dp"/>
         <!--修改部分-->
    <TextView
        android:id="@+id/fruitName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
         <!--修改部分-->
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="10dp" />
         <!--修改部分-->
</LinearLayout>
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  修改MainActivity中的代码。传入LinearLayoutManager.HORIZONTAL表示让布局横行排列

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits(); // 初始化数据
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    	// 新加代码
    	layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
    	// --------
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter adapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);
    }
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瀑布式

  修改自定义布局fruit_item.xml。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="5dp">
    <ImageView
        android:id="@+id/fruitImage"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center_horizontal" />
    <TextView
        android:id="@+id/fruitName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left"
        android:layout_marginTop="10dp" />
</LinearLayout>
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  修改自定义布局fruit_item.xml。

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits(); // 初始化数据
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        /*LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);*/
        StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3,StaggeredGridLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter adapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);
    }
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