Android 学习之《第一行代码》第二版 笔记（七）UI开发的点点滴滴（四）

RecyclerView

ListView 的扩展性不好，只能实现数据的纵向滚动效果，无法实现横向滚动。
RecyclerView 不仅可以轻松实现ListView 同样的效果，还优化了ListView 中存在的各种不足之处。

RecyclerView 横向滚动

1. RecyclerView属于新增控件，需要添加相应的依赖库

2. activity_main.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="match_parent">

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

3. Fruit.java

public class Fruit {
    private String name; //水果名称
    private int imageId; //水果对应图片的资源id

    public Fruit(String name,int imageId){ //满参构造函数
        this.name = name;
        this.imageId = imageId;
    }

    public String getName(){ //获取水果名称
        return name;
    }

    public int getImageId(){ //获取水果对应图片资源id
        return imageId;
    }
}

4. fruit_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="100dp"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/fruit_image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"/>
    <!--用于显示水果的图片-->
    <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" />
    <!--用于显示水果名称，并让TextView在垂直方向上居中显示，左外边距为10dp-->
</LinearLayout>

5. FruitAdapter.java

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.List;

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

    private List<Fruit> mFruitList;
    //静态内部类，用于缓存子项控件实例
    static class ViewHolder extends RecyclerView.ViewHolder{
        ImageView fruitImage;
        TextView fruitName;
        //静态内部类的构造函数，参数view通常就是RecyclerView子项的最外层布局
        public ViewHolder (View view){
            super(view);
            fruitImage = (ImageView)view.findViewById(R.id.fruit_image);
            fruitName = (TextView)view.findViewById(R.id.fruit_name);
        }
    }

    //构造函数
    public FruitAdapter(List<Fruit> fruitList){
        mFruitList = fruitList;
    }

    //用于告诉RecyclerView一共有多少子项，直接返回数据源的长度即可
    @Override
    public int getItemCount() {
        return mFruitList.size();
    }

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

    //用于创建ViewHolder实例
    @Override
    public FruitAdapter.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;
    }
}

6. MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private List<Fruit> mFruitList = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();//初始化水果数据
        RecyclerView recyclerView = findViewById(R.id.recycler_view); //获取RecyclerView实例
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);//用于指定RecyclerView的布局方式
        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);//设置布局的排列方向
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter adapter = new FruitAdapter(mFruitList);
        recyclerView.setAdapter(adapter);
    }

    //初始化水果数据，传入水果名称和对应的图片资源id，循环两遍是为了充满整个屏幕，达到演示效果
    private void initFruits(){
        for (int i = 0 ; i < 2 ; i++){
            Fruit apple = new Fruit("Apple",R.drawable.apple_pic);
            mFruitList.add(apple);
            Fruit banana = new Fruit("Banana",R.drawable.banana_pic);
            mFruitList.add(banana);
            Fruit orange = new Fruit("Orange",R.drawable.orange_pic);
            mFruitList.add(orange);
            Fruit watermelon = new Fruit("Watermelon",R.drawable.watermelon_pic);
            mFruitList.add(watermelon);
            Fruit pear = new Fruit("Pear",R.drawable.pear_pic);
            mFruitList.add(pear);
            Fruit grape = new Fruit("Grape",R.drawable.grape_pic);
            mFruitList.add(grape);
            Fruit pineapple = new Fruit("Pineapple",R.drawable.pineapple_pic);
            mFruitList.add(pineapple);
            Fruit strawberry = new Fruit("Strawberry",R.drawable.strawberry_pic);
            mFruitList.add(strawberry);
            Fruit cherry = new Fruit("Cherry",R.drawable.cherry_pic);
            mFruitList.add(cherry);
            Fruit mango = new Fruit("Mango",R.drawable.mango_pic);
            mFruitList.add(mango);
        }
    }
}

---

整理学习自郭霖大佬的《第一行代码》
目前小白一名，持续学习Android中，如有错误请批评指正！