Android入门之RecyclerView

1. RecycleView简介

和ListView一样的，RecyclerView控件也是为了在有限的窗口中展示大量数据集，但是提供了更为高度的灵活性以及可定制性，同时提高了运行的效率(与RecyclerView相比，ListView的性能需要一些小手段提升它的运行性能，如增加一个ViewHolder 的缓存内部类 )，相对这也提升RecyclerView的开发上手难度。

2. RecyclerView的基本使用过程

1)在Acitivity的布局xml中加入RecyclerView

2)准备数据

3)构建以及设置布局管理器

4)构建以及设置适配器

3. 添加依赖库

由于RecyclerView属于新增的控件，其定义在support库当中，要使用RecyclerView需要先在项目build.gradle中添加相应的依赖，在app/build.gradle文件中，于dependencies闭包中添加

 compile 'com.android.support:recyclerview-v7:25.3.1'

4.添加RecyclerView布局

5. 与ListView类似的实现

首先定义一个Fruit.java的子项数据类

package edu.nju.recyclerviewtest;

/**
 * Created by apple on 2017/5/1.
 */

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;
    }
}

当然该子项的xml布局也不能漏下，fruit_item.xml

适配器代码，其继承自RecyclerView.Adapter，指定起泛型为FruitAdapter.ViewHolder。ViewHolder代表着子项的布局。FruitAdapter需要重写onCreateViewHolder()(创建ViewHolder的实例)、onBindViewHolder()(对RecyclerView子项的数据进行赋值，在每个子项被滚到到屏幕内进行执行)、getItemCount()(获取RecyclerView子项的数量)

package edu.nju.recyclerviewtest;

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;

/**
 * Created by apple on 2017/5/1.
 */

public class FruitAdapter extends RecyclerView.Adapter {
    private List mFruitList;


    public FruitAdapter(List 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);



        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();
    }


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

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

MainActivity代码

package edu.nju.recyclerviewtest;

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

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

public class MainActivity extends AppCompatActivity {

    private String[] data = {"Apple", "Balana", "Orange", "Watermelon", "pear"
            , "Grape", "Pineapple", "Strawberry", "Cherry", "Mango", "Pineapple", "Strawbery"
            , "Cherry", "Mango"};
    private List fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //构造数据
        initFruits();


        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        //构造与装配布局管理器
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(linearLayoutManager);

        //构造与装配适配器
        FruitAdapter adapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);

    }

    private void initFruits() {
        for (int i = 0; i < 2; i++) {
            Fruit apple = new Fruit("Apple", R.drawable.apple_pic);
            fruitList.add(apple);
            Fruit banana = new Fruit("Banana", R.drawable.banana_pic);
            fruitList.add(banana);
            Fruit orange = new Fruit("Orange", R.drawable.orange_pic);
            fruitList.add(orange);
            Fruit watermelon = new Fruit("Watermelon", R.drawable.watermelon_pic);
            fruitList.add(watermelon);
            Fruit pear = new Fruit("Pear", R.drawable.pear_pic);
            fruitList.add(pear);
            Fruit grape = new Fruit("Grape", R.drawable.grape_pic);
            fruitList.add(grape);
            Fruit pineapple = new Fruit("Pineapple", R.drawable.pineapple_pic);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit("Strawberry", R.drawable.strawberry_pic);
            fruitList.add(strawberry);
            Fruit cherry = new Fruit("Cherry", R.drawable.cherry_pic);
            fruitList.add(cherry);
            Fruit mango = new Fruit("Mango", R.drawable.mango_pic);
            fruitList.add(mango);
        }
    }



}

运行效果

6. 横向滚动

ListView只能做到纵向滚动，作为它的升级版，可高度定制的RecyclerView可以轻松做到横向滚动的效果

修改fruit_item.xml，让水平排列的的布局元素变成垂直排列，从而适用于横向滚动

同时需要修改MainActivity中的布局管理器的设置，LinearLayoutManager的默认布局排列方向事纵向，这里将其修改为横向排列

  //构造与装配布局管理器
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        linearLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
        recyclerView.setLayoutManager(linearLayoutManager);

其他保持不变
效果如下

7. 布局管理器

RecyclerView.LayoutManager负责了RecyclerView中布局排列的，这与ListView中自身管理布局排列不同，这也是RecyclerView中优秀的设计之一。系统提供了三种内置的布局排列方式，第一种LinerLayoutManager是 线性布局，就是上述的例子，第二种是GridLayoutManager即表格布局，第三种StaggeredGridLayout即瀑布流布局

8. GridLayoutManager

在上一个例子的基础上，直接修改MainActivity中的布局管理器配置

       //构造与装配布局管理器
        GridLayoutManager layoutManager = new GridLayoutManager(this, 3);
        recyclerView.setLayoutManager(layoutManager);

其他保持不变

效果如下

9. StaggeredGridLayout

在GridLayout布局中，子项的长度是一定的，为了实现子项的长度自适应，下面用StaggeredGridLayout对上述例子进行改进，同时对子项添加点击事件。

首先还是修改fruit_item.xml中的布局元素，为了展示效果更为明显

修改MainActivity中的布局管理器以及数据初始化过程，增加文字的长度

package edu.nju.recyclerviewtest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.View;

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

public class MainActivity extends AppCompatActivity {

    private String[] data = {"Apple", "Balana", "Orange", "Watermelon", "pear"
            , "Grape", "Pineapple", "Strawberry", "Cherry", "Mango", "Pineapple", "Strawbery"
            , "Cherry", "Mango"};
    private List fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //构造数据
        initFruits();


        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        //构造与装配布局管理器
        StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);

        //构造与装配适配器
        FruitAdapter adapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);

    }
    private void initFruits() {
        for (int i = 0; i < 2; i++) {
            Fruit apple = new Fruit(getRandomLengthName("Apple"), R.drawable.apple_pic);
            fruitList.add(apple);
            Fruit banana = new Fruit(getRandomLengthName("Banana"), R.drawable.banana_pic);
            fruitList.add(banana);
            Fruit orange = new Fruit(getRandomLengthName("Orange"), R.drawable.orange_pic);
            fruitList.add(orange);
            Fruit watermelon = new Fruit(getRandomLengthName("Watermelon"), R.drawable.watermelon_pic);
            fruitList.add(watermelon);
            Fruit pear = new Fruit(getRandomLengthName("Pear"), R.drawable.pear_pic);
            fruitList.add(pear);
            Fruit grape = new Fruit(getRandomLengthName("Grape"), R.drawable.grape_pic);
            fruitList.add(grape);
            Fruit pineapple = new Fruit(getRandomLengthName("Pineapple"), R.drawable.pineapple_pic);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit(getRandomLengthName("Strawberry"), R.drawable.strawberry_pic);
            fruitList.add(strawberry);
            Fruit cherry = new Fruit(getRandomLengthName("Cherry"), R.drawable.cherry_pic);
            fruitList.add(cherry);
            Fruit mango = new Fruit(getRandomLengthName("Mango"), R.drawable.mango_pic);
            fruitList.add(mango);
        }
    }

    private String getRandomLengthName(String name) {
        Random random = new Random();
        int length = random.nextInt(20) + 1;
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < length; i++) {
            builder.append(name);
        }
        return builder.toString();
    }

}

添加点击事件。RecyclerView并没有提供setOnItemClickListener()这样的注册监听器方法，这需要给子项具体的View去注册点击事件，提高子项内部响应的精度，就比如说希望点击子项内的图片和文字有不同的事件响应，这在ListView中是无法简单实现的。修改FruitAdapter中的代码，为子项中具体View添加点击事件

package edu.nju.recyclerviewtest;

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 android.widget.Toast;

import java.util.List;

/**
 * Created by apple on 2017/5/1.
 */

public class FruitAdapter extends RecyclerView.Adapter {
    private List mFruitList;


    public FruitAdapter(List 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);

        //为子项添加点击事件
        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 clicked view " + fruit.getName(), Toast.LENGTH_SHORT).show();;
            }
        });

        //为子项中的image添加点击事件
        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 clicked image " + fruit.getName(), Toast.LENGTH_SHORT).show();;
            }
        });

        //为子项中的name添加点击事件
        holder.fruitName.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(v.getContext(), "You clicked text " + fruit.getName(), Toast.LENGTH_SHORT).show();;
            }
        });


        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();
    }


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

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

效果如下

10. 参考书籍

《第一行代码——Android》 郭霖