Android RecyclerView 使用例子

1.RecyclerView是什么？

  RecylerView是support-v7包中的新组件，是一个强大的滑动组件，与经典的ListView相比，同样拥有item回收复用的功能，这一点从它的名字recylerview即回收view也可以看出。看到这也许有人会问，不是已经有ListView了吗，为什么还要RecylerView呢？这就牵扯到第二个问题了。

2.RecyclerView的优点是什么？

根据官方的介绍RecylerView是ListView的升级版，既然如此那RecylerView必然有它的优点，现就RecylerView相对于ListView的优点罗列如下：

①RecylerView封装了viewholder的回收复用，也就是说RecylerView标准化了ViewHolder，编写Adapter面向的是ViewHolder而不再是View了，复用的   逻辑被封装了，写起来更加简单。

②提供了一种插拔式的体验，高度的解耦，异常的灵活，针对一个Item的显示RecylerView专门抽取出了相应的类，来控制Item的显示，使其的扩展性非常强。例如：你想控制横向或者纵向滑动列表效果可以通过LinearLayoutManager这个类来进行控制(与GridView效果对应的是GridLayoutManager,与瀑布流对应的还有StaggeredGridLayoutManager等)，也就是说RecylerView不再拘泥于ListView的线性展示方式，它也可以实现GridView的效果等多种效果。你想控制Item的分隔线，可以通过继承RecylerView的ItemDecoration这个类，然后针对自己的业务需求去抒写代码。

③可以控制Item增删的动画，可以通过ItemAnimator这个类进行控制，当然针对增删的动画，RecylerView有其自己默认的实现。

使用RecyclerView 需要在build.gradle引入

compile 'com.android.support:design:23.1.0'

或者

compile 'com.android.support:appcompat-v7:22.2.1'compile 'com.android.support:recyclerview-v7:22.2.1'

效果图：

每个item布局item.xml：

<?xml version="1.0" encoding="utf-8"?><FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:background="#44ff0000"    android:layout_height="wrap_content" >    <TextView        android:id="@+id/id_num"        android:layout_width="wrap_content"        android:layout_height="30dp"        android:layout_gravity="left"        android:text="左边" />    <TextView        android:id="@+id/id_num2"        android:layout_width="wrap_content"        android:layout_height="30dp"        android:layout_gravity="right"        android:text="右边" /></FrameLayout>

主窗体activity_main.xml布局：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout 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"    tools:context="com.android.mx.myapplication.MainActivity">    <android.support.v7.widget.RecyclerView        android:id="@+id/id_recyclerview"        android:divider="#ffff0000"        android:dividerHeight="10dp"        android:layout_width="match_parent"        android:layout_height="match_parent" /></RelativeLayout>

 主窗体MainActivity.java:

package com.android.mx.myapplication;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.support.v7.widget.LinearLayoutManager;import android.support.v7.widget.RecyclerView;import android.util.Log;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.TextView;import android.widget.Toast;import java.util.ArrayList;import java.util.List;public class MainActivity extends AppCompatActivity {    private RecyclerView mRecyclerView;    private List<String> mDatas;    private HomeAdapter mAdapter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        initData();        mRecyclerView = (RecyclerView) findViewById(R.id.id_recyclerview);        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));        mAdapter = new HomeAdapter();        mAdapter.setOnItemClickListener(new OnItemClickListener() {            @Override            public void onItemClick(View view, int position) {                Toast.makeText(MainActivity.this, "Click" + mDatas.get(position), Toast.LENGTH_SHORT).show();            }            @Override            public void onItemLongClick(View view, int position) {                mAdapter.remove(position); //remove the item                Toast.makeText(MainActivity.this, "LongClick" + mDatas.get(position), Toast.LENGTH_SHORT).show();            }        });        mRecyclerView.setAdapter(mAdapter);        mRecyclerView.addItemDecoration(new DividerItemDecoration(MainActivity.this, LinearLayoutManager.VERTICAL));    }    protected void initData() {        mDatas = new ArrayList<String>();        for (int i = 'A'; i < 'z'; i++) {            mDatas.add("" + (char) i);        }    }    interface OnItemClickListener {        public void onItemClick(View view, int position);        public void onItemLongClick(View view, int position);    }    public class HomeAdapter extends RecyclerView.Adapter<HomeAdapter.ItemViewHolder> {        private OnItemClickListener mOnItemClickListener;        @Override        public ItemViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {            ItemViewHolder holder = new ItemViewHolder(LayoutInflater.from(                    MainActivity.this).inflate(R.layout.item, parent,                    false));            return holder;        }        @Override        public void onBindViewHolder(final ItemViewHolder itemViewHolder, int position) {            itemViewHolder.mTextView.setText(mDatas.get(position));            if (mOnItemClickListener != null) {                /**                 * 这里加了判断，itemViewHolder.itemView.hasOnClickListeners()                 * 目的是减少对象的创建，如果已经为view设置了click监听事件,就不用重复设置了                 * 不然每次调用onBindViewHolder方法，都会创建两个监听事件对象，增加了内存的开销                 */                if (!itemViewHolder.itemView.hasOnClickListeners()) {                    Log.e("ListAdapter", "setOnClickListener");                    itemViewHolder.itemView.setOnClickListener(new View.OnClickListener() {                        @Override                        public void onClick(View v) {                            int pos = itemViewHolder.getPosition();                            mOnItemClickListener.onItemClick(v, pos);                        }                    });                    itemViewHolder.itemView.setOnLongClickListener(new View.OnLongClickListener() {                        @Override                        public boolean onLongClick(View v) {                            int pos = itemViewHolder.getPosition();                            mOnItemClickListener.onItemLongClick(v, pos);                            return true;                        }                    });                }            }        }        /**         * 移除指定位置元素         *         * @param position         * @return         */        public String remove(int position) {            if (position > mDatas.size() - 1) {                return null;            }            String value = mDatas.remove(position);            notifyItemRemoved(position);            return value;        }        public void setOnItemClickListener(OnItemClickListener mOnItemClickListener) {            this.mOnItemClickListener = mOnItemClickListener;        }        @Override        public int getItemCount() {            return mDatas.size();        }        /**         * 处理item的点击事件和长按事件         */        class ItemViewHolder extends RecyclerView.ViewHolder {            private TextView mTextView;            public ItemViewHolder(View itemView) {                super(itemView);                mTextView = (TextView) itemView.findViewById(R.id.id_num);            }        }    }}

  可以通过RecyclerView.addItemDecoration(ItemDecoration decoration)这个方法进行设置，其中它需要的参数就是我们自己定义的继承自ItemDecoration的一个对象。我们可以创建一个继承RecyclerView.ItemDecoration类来绘制分隔线，通过ItemDecoration可以让我们每一个Item从视觉上面相互分开来，例如ListView的divider非常相似的效果。当然像我们上面的例子ItemDecoration我们没有设置也没有报错，那说明ItemDecoration我们并不是强制需要使用，作为我们开发者可以设置或者不设置Decoration的。实现一个ItemDecoration，系统提供的ItemDecoration是一个抽象类，内部除去已经废弃的方法以外，我们主要实现以下三个方法:

public static abstract class ItemDecoration {           public void onDraw(Canvas c,RecyclerView parent,State state) {             onDraw(c,parent);         }         public void onDrawOver(Canvas c,RecyclerView parent,State state) {             onDrawOver(c,parent);         }         public void getItemOffsets(RectoutRect, View view,RecyclerView parent,State state) {             getItemOffsets(outRect,((LayoutParams)view.getLayoutParams()).getViewLayoutPosition(),parent);         }     }  

又因为当我们RecyclerView在进行绘制的时候会进行绘制Decoration,那么会去调用onDraw和onDrawOver方法，那么这边我们其实只要去重写onDraw和getItemOffsets这两个方法就可以实现啦。然后LayoutManager会进行Item布局的时候，会去调用getItemOffset方法来计算每个Item的Decoration合适的尺寸，下面我们来具体实现一个Decoration，DividerItemDecoration.java:

package com.android.mx.myapplication;import android.content.Context;import android.content.res.TypedArray;import android.graphics.Canvas;import android.graphics.Rect;import android.graphics.drawable.Drawable;import android.support.v7.widget.LinearLayoutManager;import android.support.v7.widget.RecyclerView;import android.view.View;/** * Created by mxuan on 2016-07-16. */public class DividerItemDecoration extends RecyclerView.ItemDecoration {    private static final int[] ATTRS = new int[]{            android.R.attr. listDivider    };    public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;    public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;    private Drawable mDivider;    private int mOrientation;    public DividerItemDecoration(Context context, int orientation) {        final TypedArray a = context.obtainStyledAttributes(ATTRS );        mDivider = a.getDrawable(0);        a.recycle();        setOrientation(orientation);    }    public void setOrientation( int orientation) {        if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {            throw new IllegalArgumentException( "invalid orientation");        }        mOrientation = orientation;    }    @Override    public void onDraw(Canvas c, RecyclerView parent) {        if (mOrientation == VERTICAL_LIST) {            drawVertical(c, parent);        } else {            drawHorizontal(c, parent);        }    }    public void drawVertical(Canvas c, RecyclerView parent) {        final int left = parent.getPaddingLeft();        final int right = parent.getWidth() - parent.getPaddingRight();        final int childCount = parent.getChildCount();        for (int i = 0; i < childCount; i++) {            final View child = parent.getChildAt(i);            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child                    .getLayoutParams();            final int top = child.getBottom() + params.bottomMargin;            final int bottom = top + mDivider.getIntrinsicHeight();            mDivider.setBounds(left, top, right, bottom);            mDivider.draw(c);        }    }    public void drawHorizontal(Canvas c, RecyclerView parent) {        final int top = parent.getPaddingTop();        final int bottom = parent.getHeight() - parent.getPaddingBottom();        final int childCount = parent.getChildCount();        for (int i = 0; i < childCount; i++) {            final View child = parent.getChildAt(i);            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child                    .getLayoutParams();            final int left = child.getRight() + params.rightMargin;            final int right = left + mDivider.getIntrinsicHeight();            mDivider.setBounds(left, top, right, bottom);            mDivider.draw(c);        }    }    @Override    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {        if (mOrientation == VERTICAL_LIST) {            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());        }else{            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);        }    }}

改变分隔线样式

     那么怎么更改分隔线的样式呢？在上面的DividerItemDecoration这个类中可以看到这个分隔线是跟ListView一样的，即系统的默认的样式，因此我们可以在styles的xml文件中进行更改，更改如下：

<resources>    <!-- Base application theme. -->    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">        <!-- Customize your theme here. -->        <item name="colorPrimary">@color/colorPrimary</item>        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>        <item name="colorAccent">@color/colorAccent</item>        <item name="android:listDivider">@drawable/divider_bg</item>    </style></resources>