RecyclerView 详解

Posted by JackPeng on June 25, 2016

概述

RecyclerView更灵活的实现了列表数据的展现,只负责View复用这块,把原来ListView中的布局方式抽象成LayoutManager,提供了一种插拔式的体验,高度的解耦,异常的灵活,通过设置它提供的不同LayoutManager,ItemDecoration , ItemAnimator实现令人瞠目的效果。

你想要控制其显示的方式,请通过布局管理器LayoutManager

你想要控制Item间的间隔(可绘制),请通过ItemDecoration

你想要控制Item增删的动画,请通过ItemAnimator

基本使用

RecyclerView包含在android的support v7包中,因此使用前需要在build.gradle中导入:

  compile 'com.android.support:recyclerview-v7:23.2.0'

使用步骤一般如下:

    recyclerView = (RecyclerView) findViewById(R.id.recycler);
    recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));//设置竖直方向的线性manager
    //recyclerView.addItemDecoration(new MyItemDecoration());//添加divider,非必须
    recyclerView.setAdapter(new MyRecycleAdapter());//设置adapter

值得一提的是,原来我们熟悉的ViewHolder终于被v7库封装了,adapter实现类如下:

 class MyRecycleAdapter extends RecyclerView.Adapter {
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        MyViewHolder holder = new MyViewHolder(LayoutInflater.from(RecyclerViewDemo.this).inflate(R.layout.recycler_item, parent, false));
        return holder;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {//绑定数据

    }

    @Override
    public int getItemCount() {
        return 20;
    }

}

recycler_item布局文件如下:

<?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="wrap_content"
    android:gravity="center"
    android:background="#00ff00"
    android:orientation="vertical">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/logo" />

</LinearLayout>

默认显示效果如下:

image

可以看到是没有divider分割线的,需要我们自己实现,下边研究如何实现divider。

Divider实现

我们可以通过该方法添加分割线: mRecyclerView.addItemDecoration() 该方法的参数为RecyclerView.ItemDecoration,该类为抽象类,官方目前并没有提供默认的实现类(我觉得最好能提供几个)。

该类的源码如下:

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(Rect outRect, View view, RecyclerView parent, State state) {
            getItemOffsets(outRect, ((LayoutParams)         view.getLayoutParams()).getViewLayoutPosition(),
                parent);
}

@Deprecated
public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        outRect.set(0, 0, 0, 0);
 }

当我们调用mRecyclerView.addItemDecoration()方法添加decoration的时候,RecyclerView在绘制的时候,会去绘制decorator,即调用该类的onDraw和onDrawOver方法,

onDraw方法先于drawChildren

onDrawOver在drawChildren之后,一般我们选择复写其中一个即可。

getItemOffsets 可以通过outRect.set()为每个Item设置一定的偏移量,主要用于绘制Decorator。

接下来我们看一个RecyclerView.ItemDecoration的实现类,该类很好的实现了RecyclerView添加分割线(当使用LayoutManager为LinearLayoutManager时),来自于v7包的sample中:

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 +
                Math.round(ViewCompat.getTranslationY(child));
        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 +
                Math.round(ViewCompat.getTranslationX(child));
        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);
    }
}
}

如果设置的是GridLayoutManager,则以上divider就不能满足需求了。主要是因为它在绘制的时候,比如水平线,针对每个child的取值为:

final int left = parent.getPaddingLeft();
final int right = parent.getWidth() - parent.getPaddingRight();

因为每个Item一行,这样是没问题的。而GridLayoutManager时,一行有多个childItem,这样就多次绘制了(需要针对child逐一绘制),并且GridLayoutManager时,Item如果为最后一列(则右边无间隔线)或者为最后一行(底部无分割线)。 针对上述,我们编写了DividerGridItemDecoration:

class DividerGridItemDecoration extends RecyclerView.ItemDecoration {

    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};
    private Drawable mDivider;

    public DividerGridItemDecoration(Context context) {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {

        drawHorizontal(c, parent);
        drawVertical(c, parent);

    }

    private int getSpanCount(RecyclerView parent) {
        // 列数
        int spanCount = -1;
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {

            spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            spanCount = ((StaggeredGridLayoutManager) layoutManager)
                    .getSpanCount();
        }
        return spanCount;
    }

    public void drawHorizontal(Canvas c, RecyclerView parent) {
        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.getLeft() - params.leftMargin;
            final int right = child.getRight() + params.rightMargin
                    + mDivider.getIntrinsicWidth();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    public void drawVertical(Canvas c, RecyclerView parent) {
        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.getTop() - params.topMargin;
            final int bottom = child.getBottom() + params.bottomMargin;
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicWidth();

            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    private boolean isLastColum(RecyclerView parent, int pos, int spanCount,
                                int childCount) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            if ((pos + 1) % spanCount == 0)// 如果是最后一列,则不需要绘制右边
            {
                return true;
            }
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            int orientation = ((StaggeredGridLayoutManager) layoutManager)
                    .getOrientation();
            if (orientation == StaggeredGridLayoutManager.VERTICAL) {
                if ((pos + 1) % spanCount == 0)// 如果是最后一列,则不需要绘制右边
                {
                    return true;
                }
            } else {
                childCount = childCount - childCount % spanCount;
                if (pos >= childCount)// 如果是最后一列,则不需要绘制右边
                    return true;
            }
        }
        return false;
    }

    private boolean isLastRaw(RecyclerView parent, int pos, int spanCount,
                              int childCount) {
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager) {
            childCount = childCount - childCount % spanCount;
            if (pos >= childCount)// 如果是最后一行,则不需要绘制底部
                return true;
        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
            int orientation = ((StaggeredGridLayoutManager) layoutManager)
                    .getOrientation();
            // StaggeredGridLayoutManager 且纵向滚动
            if (orientation == StaggeredGridLayoutManager.VERTICAL) {
                childCount = childCount - childCount % spanCount;
                // 如果是最后一行,则不需要绘制底部
                if (pos >= childCount)
                    return true;
            } else
            // StaggeredGridLayoutManager 且横向滚动
            {
                // 如果是最后一行,则不需要绘制底部
                if ((pos + 1) % spanCount == 0) {
                    return true;
                }
            }
        }
        return false;
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition,
                               RecyclerView parent) {
        int spanCount = getSpanCount(parent);
        int childCount = parent.getAdapter().getItemCount();
        if (isLastRaw(parent, itemPosition, spanCount, childCount))// 如果是最后一行,则不需要绘制底部
        {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        } else if (isLastColum(parent, itemPosition, spanCount, childCount))// 如果是最后一列,则不需要绘制右边
        {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(),
                    mDivider.getIntrinsicHeight());
        }
    }
} 主要在getItemOffsets方法中,去判断如果是最后一行,则不需要绘制底部;如果是最后一列,则不需要绘制右边,整个判断也考虑到了StaggeredGridLayoutManager的横向和纵向,所以稍稍有些复杂。最重要还是去理解,如何绘制什么的不重要。

一般如果仅仅是希望有空隙,还是去设置item的margin方便。

Adapter实现

Adapter需要继承RecyclerView内部定义的Adapter,和BaseAdapter类似,最简单情况下实现以下几个方法即可:

class MyRecycleAdapter extends RecyclerView.Adapter {
    /**
     * 绑定holder中的view
     *
     * @param parent
     * @param viewType
     * @return
     */
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View item = LayoutInflater.from(RecyclerViewDemo.this).inflate(R.layout.recycler_item, parent, false);
        MyViewHolder holder = new MyViewHolder(item);
        holder.imageView = (ImageView) item.findViewById(R.id.itemimage);
        return holder;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (position % 2 == 0) {
           ViewGroup.LayoutParams params = holder.itemView.getLayoutParams();
            params.height=params.height/2;
            holder.itemView.setLayoutParams(params);
        }
    }

    @Override
    public int getItemCount() {
        return 20;
    }

}  除此之外,还有getItemViewType等方法,大部分方法和BaseAdapter是一一对应的。

LayoutManage使用

有3个实现类,类继承结构如下:

image

从名字上很好理解:

LinearLayoutManger:线性布局,支持水平和竖直两个方向,可通过参数指定;

GridLayoutManager:类似于gridview的布局方式;

recyclerView.setLayoutManager(new GridLayoutManager(this,3));//3列的gridview

StaggeredGridLayoutManager:瀑布流效果的布局方式,其实他可以实现GridLayoutManager一样的功能,仅仅按照下列代码:

/ mRecyclerView.setLayoutManager(new GridLayoutManager(this,3));
    mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(3,        StaggeredGridLayoutManager.VERTICAL));

这两种写法显示的效果是一致的,但是注意StaggeredGridLayoutManager构造的第二个参数传一个orientation,如果传入的是StaggeredGridLayoutManager.VERTICAL代表有多少列;那么传入的如果是StaggeredGridLayoutManager.HORIZONTAL就代表有多少行,比如本例如果改为:

mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(4,
    StaggeredGridLayoutManager.HORIZONTAL));

那么效果为:

image

可以看到,固定为4行,变成了左右滑动。有一点需要注意,如果是横向的时候,item的宽度需要注意去设置,毕竟横向的宽度没有约束了,应为控件可以横向滚动了。

如果让你去实现个瀑布流,最起码不是那么随意就可以实现的吧?但是,如果使用RecyclerView,分分钟的事。 那么如何实现?其实你什么都不用做,只要使用StaggeredGridLayoutManager我们就已经实现了,只是上面的item布局我们使用了固定的高度,下面我们仅仅在适配器的onBindViewHolder方法中为我们的item设置个随机的高度(代码就不贴了,最后会给出源码下载地址),看看效果图:

image

通过RecyclerView去实现ListView、GridView、瀑布流的效果基本上没有什么区别,而且可以仅仅通过设置不同的LayoutManager即可实现。还有更nice的地方,就在于item增加、删除的动画也是可配置的。接下来看一下ItemAnimator。

ItemAnimator

ItemAnimator也是一个抽象类,好在系统为我们提供了一种默认的实现类,期待系统多 添加些默认的实现。

借助默认的实现,当Item添加和移除的时候,添加动画效果很简单:

 // 设置item动画
mRecyclerView.setItemAnimator(new DefaultItemAnimator()); 系统为我们提供了一个默认的实现,我们为我们的瀑布流添加以上一行代码,效果为:

image

如果是GridLayoutManager呢?动画效果为:

image

注意,这里更新数据集不是用adapter.notifyDataSetChanged()而是 notifyItemInserted(position)与notifyItemRemoved(position) 否则没有动画效果。 当然了只提供了一种动画,那么我们肯定可以去自定义各种nice的动画效果。 高兴的是,github上已经有很多类似的项目了,这里我们直接引用下:RecyclerViewItemAnimators,大家自己下载查看。 提供了SlideInOutLeftItemAnimator,SlideInOutRightItemAnimator, SlideInOutTopItemAnimator,SlideInOutBottomItemAnimator等动画效果。

Click and LongClick

系统没有提供ClickListener和LongClickListener。 不过我们也可以自己去添加,只是会多了些代码而已。 实现的方式比较多,你可以通过mRecyclerView.addOnItemTouchListener去监听然后去判断手势, 当然你也可以通过adapter中自己去提供回调,这里我们选择后者,前者的方式,大家有兴趣自己去实现。

那么代码也比较简单:

class HomeAdapter extends RecyclerView.Adapter<HomeAdapter.MyViewHolder>
{

//...
public interface OnItemClickLitener
{
    void onItemClick(View view, int position);
    void onItemLongClick(View view , int position);
}

private OnItemClickLitener mOnItemClickLitener;

public void setOnItemClickLitener(OnItemClickLitener mOnItemClickLitener)
{
    this.mOnItemClickLitener = mOnItemClickLitener;
}

@Override
public void onBindViewHolder(final MyViewHolder holder, final int position)
{
    holder.tv.setText(mDatas.get(position));

    // 如果设置了回调,则设置点击事件
    if (mOnItemClickLitener != null)
    {
        holder.itemView.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                int pos = holder.getLayoutPosition();
                mOnItemClickLitener.onItemClick(holder.itemView, pos);
            }
        });

        holder.itemView.setOnLongClickListener(new OnLongClickListener()
        {
            @Override
            public boolean onLongClick(View v)
            {
                int pos = holder.getLayoutPosition();
                mOnItemClickLitener.onItemLongClick(holder.itemView, pos);
                return false;
            }
        });
    }
}
//...
}  adapter中自己定义了个接口,然后在onBindViewHolder中去为holder.itemView去设置相应  的监听最后回调我们设置的监听。Activity中去设置监听:

mAdapter.setOnItemClickLitener(new OnItemClickLitener()
    {

        @Override
        public void onItemClick(View view, int position)
        {
            Toast.makeText(HomeActivity.this, position + " click",
                    Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onItemLongClick(View view, int position)
        {
            Toast.makeText(HomeActivity.this, position + " long click",
                    Toast.LENGTH_SHORT).show();
                    mAdapter.removeData(position);
        }
    });

整个体验下来,感觉这种插拔式的设计太棒了,如果系统再能提供一些常用的分隔符,多添加些动画效果就更好了。

通过简单改变下LayoutManager,就可以产生不同的效果,那么我们可以根据手机屏幕的宽度去动态设置LayoutManager,屏幕宽度一般的,显示为ListView;宽度稍大的显示两列的GridView或者瀑布流(或者横纵屏幕切换时变化,有点意思~);显示的列数和宽度成正比。甚至某些特殊屏幕,让其横向滑动~~再选择一个nice的动画效果,相信这种插件式的编码体验一定会让你迅速爱上RecyclerView。