Android控件RecyclerView的基本用法

　　RecyclerView是Android提供的一个功能强大的滚动控件，是增强版的ListView和GridView，不仅可以轻松实现和ListView相同的效果，还优化了ListView中存在的各种不足之处；目前Android官方更加推荐使用RecyclerView，本文介绍一下Android Studio中RecyclerView的基本用法。
　　RecyclerView需要通过setLayoutManager()方法设置布局管理器，RecyclerView有三个默认布局管理器LinearLayoutManager、GridLayoutManager、StaggeredGridLayoutManager，它们都支持横向和纵向排列以及反向滑动。如果想把RecyclerView改为横向滑动，可以通过调用：
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL); // 改变RecyclerView的方向
　　RecyclerView是Android新增的控件，为了让RecyclerView在所有的Android版本上都可以使用，Android团队采取了将RecyclerView定义在support库中，所以，我们如果要使用RecyclerView这个控件，首先需要在项目中的build.gradle(Module:app)中添加相应的依赖库；
　　打开build.gradle(Module:app)文件，在dependencies闭包中添加如下内容：

apply plugin: 'com.android.application'android {    compileSdkVersion 25    buildToolsVersion "25.0.2"    defaultConfig {        applicationId "neu.cn.myrecyclerview"        minSdkVersion 15        targetSdkVersion 25        versionCode 1        versionName "1.0"        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"    }    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'        }    }}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:recyclerview-v7:25.3.1'    testCompile 'junit:junit:4.12'}

　　添加过之后点击Sync Now进行同步，同步完后，接下来修改主布局activity_main.xml，如下：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="neu.cn.myrecyclerview.MainActivity">    <LinearLayout        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:orientation="horizontal">        <Button            android:id="@+id/add_item"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:text="Add Item"            android:textAllCaps="false" />        <Button            android:id="@+id/delete_item"            android:layout_width="0dp"            android:layout_height="wrap_content"            android:layout_weight="1"            android:text="Delete Item"            android:textAllCaps="false" />    </LinearLayout>    <android.support.v7.widget.RecyclerView        android:id="@+id/recycler_view"        android:layout_width="match_parent"        android:layout_height="match_parent" /></LinearLayout>

　　在布局中加入RecyclerView控件，需要注意的是，由于RecyclerView并不是内置在系统SDK中的，所以需要把完整的包路径写出来；
　　为RecyclerView新建一个适配器类FruitAdapter，并让其继承自RecyclerView.Adapter，并指定其泛型为FruitAdapter.MyViewHolder，MyViewHolder是FruitAdapter的内部类；如下：

package neu.cn.myrecyclerview;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;import java.util.Random;/** * Created by neuHenry on 2017/6/1. */public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.MyViewHolder> {    private List<Fruit> mFruitList;    public FruitAdapter(List<Fruit> mFruitList) {        this.mFruitList = mFruitList;    }    @Override    public MyViewHolder onCreateViewHolder(final ViewGroup parent, int viewType) {        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);        final MyViewHolder holder = new MyViewHolder(view);        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 fruitView " + fruit.getImageName(), 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 clicked fruitImage " + fruit.getImageName(), Toast.LENGTH_SHORT).show();            }        });        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 fruitName " + fruit.getImageName(), Toast.LENGTH_SHORT).show();            }        });        return holder;    }    @Override    public void onBindViewHolder(MyViewHolder holder, int position) {        Fruit fruit = mFruitList.get(position);        holder.fruitImage.setImageResource(fruit.getImageID());        holder.fruitName.setText(fruit.getImageName());    }    @Override    public int getItemCount() {        return mFruitList.size();    }    /**     * RecyclerView 中动态添加Item     * @param position     */    public void addItem(int position) {        Random random = new Random(mFruitList.size());        int index = random.nextInt(mFruitList.size());        Fruit fruit = mFruitList.get(index);        mFruitList.add(fruit);        notifyItemInserted(position);    }    /**     * RecyclerView 中动态删除Item     * @param position     */    public void deleteItem(int position) {        mFruitList.remove(position);        notifyItemRemoved(position);    }    class MyViewHolder extends RecyclerView.ViewHolder {        View fruitView;        ImageView fruitImage;        TextView fruitName;        public MyViewHolder(View view) {            super(view);            fruitView = view;            fruitImage = (ImageView) view.findViewById(R.id.fruit_image);            fruitName = (TextView) view.findViewById(R.id.fruit_name);        }    }}

fruit_item.xml的代码如下：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_margin="5dp"    android:orientation="horizontal">    <ImageView        android:id="@+id/fruit_image"        android:layout_width="wrap_content"        android:layout_height="wrap_content" />    <TextView        android:id="@+id/fruit_name"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_gravity="center_vertical"        android:layout_marginLeft="10dp" /></LinearLayout>

Fruit.java的代码如下：

package neu.cn.myrecyclerview;/** * Created by neuHenry on 2017/6/1. */public class Fruit {    private int imageID;    private String imageName;    public Fruit(int imageID, String imageName) {        this.imageID = imageID;        this.imageName = imageName;    }    public int getImageID() {        return imageID;    }    public String getImageName() {        return imageName;    }}

修改MainActivity中的代码，如下：

package neu.cn.myrecyclerview;import android.content.Context;import android.graphics.Canvas;import android.os.Build;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.support.v7.widget.DefaultItemAnimator;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.support.v7.widget.helper.ItemTouchHelper;import android.util.DisplayMetrics;import android.view.View;import android.view.WindowManager;import android.widget.Button;import java.util.ArrayList;import java.util.Collections;import java.util.List;import java.util.Random;public class MainActivity extends AppCompatActivity implements View.OnClickListener {    // 水果数据列表，存放水果数据    private List<Fruit> fruitList = new ArrayList<>();    private RecyclerView recyclerView;    private FruitAdapter fruitAdapter;    // 处理RecyclerView中Item的滑动和拖拽    private ItemTouchHelper itemTouchHelper;    private WindowManager windowManager;    private Button addItem;    private Button deleteItem;    private int screenwidth;    private Boolean remove;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initFruits();        fruitAdapter = new FruitAdapter(fruitList);        remove = false;        addItem = (Button) findViewById(R.id.add_item);        deleteItem = (Button) findViewById(R.id.delete_item);        windowManager = (WindowManager) MainActivity.this.getSystemService(Context.WINDOW_SERVICE);        DisplayMetrics outMetrics = new DisplayMetrics();        windowManager.getDefaultDisplay().getMetrics(outMetrics);        screenwidth = outMetrics.widthPixels; // 获取屏幕宽度        addItem.setOnClickListener(this);        deleteItem.setOnClickListener(this);        itemTouchHelper = new ItemTouchHelper(new ItemTouchHelper.Callback() {            // 用于设置拖拽和滑动的方向            @Override            public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {                int dragFlags = 0, swipeFlags = 0;                if (recyclerView.getLayoutManager() instanceof StaggeredGridLayoutManager || recyclerView.getLayoutManager() instanceof GridLayoutManager) {                    // 瀑布流和网格布局有四个拖拽方向                    dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;                } else if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {                    // 线性布局有两个拖拽方向                    dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;                    // 设置侧滑方向为从两个方向都可以                    swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;                }                return makeMovementFlags(dragFlags, swipeFlags);            }            // 长摁Item拖拽时会回调这个方法            @Override            public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {                int from = viewHolder.getAdapterPosition();                int to = target.getAdapterPosition();                Collections.swap(fruitList, from, to); // 交换fruitList中数据的位置                fruitAdapter.notifyItemMoved(from, to); // 更新适配器中item的位置                return true;            }            // 处理滑动删除操作            @Override            public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {                fruitAdapter.deleteItem(viewHolder.getAdapterPosition());                fruitAdapter.notifyDataSetChanged();            }            @Override            public boolean isLongPressDragEnabled() {                return true; // 返回true则为所有Item都设置可以拖拽            }            // 当Item拖拽开始时调用            @Override            public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {                super.onSelectedChanged(viewHolder, actionState);                if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                        viewHolder.itemView.setElevation(100);                    }                }            }            // 当Item拖拽完成时调用            @Override            public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {                super.clearView(recyclerView, viewHolder);                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                    viewHolder.itemView.setElevation(0);                }            }            // 当Item视图变化时调用            @Override            public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {                viewHolder.itemView.scrollTo(-(int) dX, -(int) dY); // 根据Item的滑动偏移修改HorizontalScrollView的滚动                if (Math.abs(dX) > screenwidth / 5 && !remove && isCurrentlyActive) {                    // 用户收滑动Item超过屏幕5分之1，标记为要删除                    remove = true;                } else if (Math.abs(dX) < screenwidth / 5 && remove && !isCurrentlyActive) {                    // 用户收滑动Item没有超过屏幕5分之1，标记为不删除                    remove = false;                }                if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE && remove == true && !isCurrentlyActive) {                    // 当用户滑动Item超过屏幕5分之1，并且松手时，执行删除Item                    if (viewHolder != null && viewHolder.getAdapterPosition() >= 0) {                        fruitAdapter.deleteItem(viewHolder.getAdapterPosition());                        remove = false;                    }                }                super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);            }        });        recyclerView = (RecyclerView) findViewById(R.id.recycler_view);        // 与RecyclView绑定        itemTouchHelper.attachToRecyclerView(recyclerView);        // 线性布局        LinearLayoutManager layoutManager = new LinearLayoutManager(this);//        layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL); // 改变RecyclerView的方向        // 网格布局//        GridLayoutManager layoutManager = new GridLayoutManager(this, 3); // 第二个参数表示每行显示的个数        // 瀑布流布局//        StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);        recyclerView.setLayoutManager(layoutManager);        recyclerView.setAdapter(fruitAdapter);        recyclerView.setItemAnimator(new DefaultItemAnimator()); // 设置Item加载或移除时的动画    }    /**     * 初始化水果数据列表     */    private void initFruits() {        for (int i = 0; i < 2; i++) {            Fruit apple = new Fruit(R.drawable.apple_pic, getRandomName("Apple"));            fruitList.add(apple);            Fruit banana = new Fruit(R.drawable.banana_pic, getRandomName("Banana"));            fruitList.add(banana);            Fruit orange = new Fruit(R.drawable.orange_pic, getRandomName("Orange"));            fruitList.add(orange);            Fruit watermelon = new Fruit(R.drawable.watermelon_pic, getRandomName("Watermelon"));            fruitList.add(watermelon);            Fruit pear = new Fruit(R.drawable.pear_pic, getRandomName("Pear"));            fruitList.add(pear);            Fruit grape = new Fruit(R.drawable.grape_pic, getRandomName("Grape"));            fruitList.add(grape);            Fruit pineapple = new Fruit(R.drawable.pineapple_pic, getRandomName("Pineapple"));            fruitList.add(pineapple);            Fruit strawberry = new Fruit(R.drawable.strawberry_pic, getRandomName("Strawberry"));            fruitList.add(strawberry);            Fruit cherry = new Fruit(R.drawable.cherry_pic, getRandomName("Cherry"));            fruitList.add(cherry);            Fruit mango = new Fruit(R.drawable.mango_pic, getRandomName("Mango"));            fruitList.add(mango);        }    }    private String getRandomName(String name) {        StringBuffer buffer = new StringBuffer();        Random random = new Random(20);        int length = random.nextInt(20);        for (int i = 0; i < length; i++) {            buffer.append(name);        }        return buffer.toString();    }    @Override    public void onClick(View v) {        switch (v.getId()) {            case R.id.add_item: // RecyclerView中添加Item                fruitAdapter.addItem(fruitList.size());                break;            case R.id.delete_item: // // RecyclerView中删除Item                fruitAdapter.deleteItem(fruitList.size() - 1);                break;            default:                break;        }    }}

运行，效果如下：
　

1、修改代码，使的RecyclerView实现水平滚动效果，把fruit_item.xml中的元素改成垂直排列，修改布局的相关属性等，如下：

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

2、修改MainActivity的代码实现水平滚动，加入：
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL); // 改变RecyclerView的方向
效果如下：

3、修改MainActivity的代码实现网格布局，如下：
GridLayoutManager layoutManager = new GridLayoutManager(this, 3); // 第二个参数表示每行显示的个数
效果如下：

4、再次修改MainActivity的代码和fruit_item的代码，实现瀑布流布局，上面的MainActivity代码就是修改后的，瀑布流布局需要各个子项高度不一致才能看出来，图片大小都一样，为此只有在TextView中多加一些字啦！效果如下所示：

　　RecyclerView不同于ListView的点击事件，RecyclerView不像ListView一样提供item的点击监听，所以需要我们自己实现给子项具体的View去注册点击事件。RecyclerView的item点击事件监听可以向我代码中为item的view设置监听，也可以在recyclerView.addOnItemTouchListener里去判断手势来实现。
　　另外，代码后续实现了通过点击按钮动态的添加和删除RecyclerView中的Item子项，通过添加和删除可以更好的理解RecyclerView的三种布局管理器；

　　ItemTouchHelper是一个处理RecyclerView的滑动删除和拖拽的辅助类，RecyclerView 的item拖拽移动和滑动删除就靠它来实现。ItemTouchHelper需要在RecyclerView初始化的时候调用
itemTouchHelper.attachToRecyclerView(recyclerView);
通过attachToRecyclerView与RecyclerView 绑定后生效，如果想要为Item设置拖拽和滑动时的响应动画效果，可以重写ItemTouchHelper的三个方法来实现：onSelectedChanged、clearView、onChildDraw，具体的实现见代码；
　　文中代码地址：MyRecyclerView