第三章 RecyclerView

一、为什么用RecyclerView来代替ListView
①ListView性能较差，需要使用一些技巧来优化它
②RecyclerView优化了ListView存在的各种不足之处

二、基本用法
1、 在build.gradle中的dependencies闭包中添加

compile 'com.android.support:recyclerview -7:25.3.1'

添加后如下

dependencies {    compile fileTree(dir: 'libs', include: ['*.jar'])    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {        exclude group: 'com.android.support', module: 'support-annotations'    })    compile 'com.android.support:appcompat-v7:25.3.1'    compile 'com.android.support.constraint:constraint-layout:1.0.2'    compile 'com.android.support:recyclerview-v7:25.3.1'    testCompile 'junit:junit:4.12'}

添加后同步即可

2、在布局中加入RecyclerView控件

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_height="match_parent"    android:layout_width="match_parent">    <android.support.v7.widget.RecyclerView        android:id="@+id/recycler_view"        android:layout_width="match_parent"        android:layout_height="match_parent"/></LinearLayout>

三、实现和ListView中的水果类相同的效果
1.将ListView例子中的fruit类和fruit_item.xml复制过来
2.新建一个FruitAdapter类

package com.example.kim.recyclerview;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 KIM on 2017/4/27. */public  class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {    private List<Fruit> mFruitList;    //定义一个内部类ViewHolder并继承RecyclerView的ViewHolder    static class   ViewHolder extends RecyclerView.ViewHolder{        ImageView fruitImage;        TextView  fruitName;    //用于获取到布局中ImageView和TextView中的实例        public ViewHolder(View view){            super(view);            fruitImage= (ImageView)view.findViewById(R.id.fruit_image);            fruitName =(TextView)view.findViewById(R.id.fruit_name);        }    }    //用于把用展现的数据源传进来        public FruitAdapter(List<Fruit>fruitList){            mFruitList=fruitList;        }    //FruitAdapter继承自Recycler.Adapter 就必须重写onCreateViewHolder()、onBindViewHolder()    //和getItemCount()    //onCreateViewHolder用于创建ViewHolder实例        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//用于对RecyclerView的每个子项进行赋值，用position来得到当前实例         public void onBindViewHolder(ViewHolder holder, int position) {            Fruit fruit = mFruitList.get(position);            holder.fruitName.setText(fruit.getName());            holder.fruitImage.setImageResource(fruit.getImageId());        }    //用于告诉Recycler有多少子项    public int getItemCount(){            return mFruitList.size();        }}

3、修改MainActivity中的代码

package com.example.kim.recyclerview;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.support.v7.widget.LinearLayoutManager;import android.support.v7.widget.RecyclerView;import android.widget.LinearLayout;import java.util.ArrayList;import java.util.List;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();        //获取RecyclerView实例        RecyclerView recyclerView=(RecyclerView)findViewById(R.id.recycler_view);        //创建一个LinearLayoutManger对象 设置到RecyclerView对象当中，用于实现RecyclerView的存在方式        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.drawable.apple_pic);            fruitList.add(apple);            Fruit mango =new Fruit("Mango",R.drawable.mango_pic);            fruitList.add(mango);            //.........省略N多水果        }}

四、实现横向滚动
1.对fruit_item进行修改

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="100dp"    //因为每种水果文字长度不同，用wrap_content的话    //RecyclerView子项会长短不一，所以使用固定值100dp    android:layout_height="wrap_content">    <ImageView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/fruit_image"        android:layout_gravity="center_horizontal"/>    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/fruit_name"        android:layout_gravity="center_horizontal"        android:layout_marginTop="10dp"/></LinearLayout>

2、对MainActivity进行修改

package com.example.kim.recyclerview;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.support.v7.widget.LinearLayoutManager;import android.support.v7.widget.RecyclerView;import android.widget.LinearLayout;import java.util.ArrayList;import java.util.List;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();        //获取RecyclerView实例        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);        //创建一个LinearLayoutManger对象 设置到RecyclerView对象当中，用于实现RecyclerView的存在方式        LinearLayoutManager layoutManager = new LinearLayoutManager(this);        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);        recyclerView.setLayoutManager(layoutManager);        FruitAdapter adapter = new FruitAdapter(fruitList);        recyclerView.setAdapter(adapter);    }    private void initFruits() {        for (int i = 0; i < 20; i++) {            Fruit apple = new Fruit("Apple", R.drawable.apple_pic);            fruitList.add(apple);            Fruit mango = new Fruit("Mango", R.drawable.mango_pic);            fruitList.add(mango);            //.........省略N多水果        }    }}

五、实现瀑布流布局(StaggeredGridManager)
1、修改fruit_item

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_margin="5dp">    <!--    这里将100dp修改成wrap_content，因为瀑布流的        宽度应根据布局的列数来自动适配-->    <ImageView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/fruit_image"        android:layout_gravity="center_horizontal"/>    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:id="@+id/fruit_name"        android:layout_gravity="left"        android:layout_marginTop="10dp"/></LinearLayout>

2、修改MainActivity

package com.example.kim.recyclerview;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.widget.LinearLayout;import java.util.ArrayList;import java.util.List;import java.util.Random;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();        //获取RecyclerView实例        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);        StaggeredGridLayoutManager layoutManager =new                StaggeredGridLayoutManager(4,StaggeredGridLayoutManager.VERTICAL);        //传入2个参数，布局列数和布局排列方向        recyclerView.setLayoutManager(layoutManager);        FruitAdapter adapter = new FruitAdapter(fruitList);        recyclerView.setAdapter(adapter);    }    private void initFruits() {        for (int i = 0; i < 20; i++) {            Fruit apple = new Fruit(getRandomLengthName("apple"), R.drawable.apple_pic);            fruitList.add(apple);            Fruit mango = new Fruit(getRandomLengthName("mango"), R.drawable.mango_pic);            fruitList.add(mango);            //.........省略N多水果        }    }    //创建一个getRandomLengthName方法，使水果的名字随机重复几次，来使瀑布流效果明显    private String getRandomLengthName(String name){        Random random = new Random();        int length = random.nextInt(20)+1;        //若不+1则产生0-19之间的整数，+1后产生1—10之间的整数        StringBuilder builder = new StringBuilder();        for(int i=0;i<length;i++){            builder.append(name);            //append（）用于字符串拼接        }        return builder.toString();    }}

六、实现网格布局(GridLayoutManager)

package com.example.kim.recyclerview;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.widget.LinearLayout;import java.util.ArrayList;import java.util.List;import java.util.Random;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();        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);        GridLayoutManager layoutManager =new                GridLayoutManager(MainActivity.this,4);        //这里传入两个参数context和布局列数        recyclerView.setLayoutManager(layoutManager);        FruitAdapter adapter = new FruitAdapter(fruitList);        recyclerView.setAdapter(adapter);    }    private void initFruits() {        for (int i = 0; i < 20; i++) {            Fruit apple = new Fruit("apple", R.drawable.apple_pic);            fruitList.add(apple);            Fruit mango = new Fruit("mango", R.drawable.mango_pic);            fruitList.add(mango);            //.........省略N多水果        }    }}

七、RecyclerView的点击事件

package com.example.kim.recyclerview;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 KIM on 2017/4/27. */public  class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {    private List<Fruit> mFruitList;    //定义一个内部类ViewHolder并继承RecyclerView的ViewHolder    static class   ViewHolder extends RecyclerView.ViewHolder{        View fruitView;        //添加fruitView        ImageView fruitImage;        TextView  fruitName;    //用于获取到布局中ImageView和TextView中的实例        public ViewHolder(View view){            super(view);            fruitView = view;            //用fruitView来保存子项最外层布局            fruitImage= (ImageView)view.findViewById(R.id.fruit_image);            fruitName =(TextView)view.findViewById(R.id.fruit_name);        }    }    //用于把用展现的数据源传进来        public FruitAdapter(List<Fruit>fruitList){            mFruitList=fruitList;        }    //FruitAdapter继承自Recycler.Adapter 就必须重写onCreateViewHolder()、onBindViewHolder()    //和getItemCount()    //onCreateViewHolder用于创建ViewHolder实例        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);            holder.fruitView.setOnClickListener(new View.OnClickListener(){                public void onClick(View v){                    int position = holder.getAdapterPosition();                    Fruit fruit=mFruitList.get(position);                    Toast.makeText(v.getContext(),"You Click View",Toast.LENGTH_SHORT).show();                }            });            holder.fruitImage.setOnClickListener(new View.OnClickListener(){                public void onClick(View v){                    int position=holder.getAdapterPosition();                    Fruit fruit=mFruitList.get(position);                    Toast.makeText(v.getContext(),"You Click Image",Toast.LENGTH_SHORT).show();                }            });            holder.fruitName.setOnClickListener(new View.OnClickListener(){                public void onClick(View v){                    int position = holder.getAdapterPosition();                    Fruit fruit = mFruitList.get(position);                    Toast.makeText(v.getContext(),"You Click Name",Toast.LENGTH_SHORT).show();                }            });            return holder;        }    @Override//用于对RecyclerView的每个子项进行赋值，用position来得到当前实例         public void onBindViewHolder(ViewHolder holder, int position) {            Fruit fruit = mFruitList.get(position);            holder.fruitName.setText(fruit.getName());            holder.fruitImage.setImageResource(fruit.getImageId());        }    //用于告诉Recycler有多少子项    public int getItemCount(){            return mFruitList.size();        }}