RecyclerView的介绍与使用

一、什么是RecyclerView

新的视图控件，是Android-support-v7-21版本中新增的一个Widgets，官方对于它的介绍则是：RecyclerView是ListView的升级版本，更加先进和灵活（继承自ViewGroup）。

二、RecyclerView的作用

由于ListView的紧耦合问题，谷歌的改进就是RecyclerView本身不参与任何视图相关的问题。

关于布局、绘制和其他相关的问题，也就是跟数据展示相关的所有问题，都被委派给了一些”插件化”的类来处理。RecyclerView只负责回收和重用的工作。

三、RecyclerView有什么

RecyclerView中用于数据展示的一些重要的内部类：

　　1、Adapter：包装数据集合并且为每个条目创建视图。

　　2、ViewHolder：保存用于显示每个数据条目的子View。

　　3、LayoutManager：将每个条目的视图放置于适当的位置。

　　4、ItemDecoration：在每个条目的视图的周围或上面绘制一些装饰视图。

　　5、ItemAnimator：在条目被添加、移除或者重排序时添加动画效果。

四、RecyclerView的优势与缺点

优势　

　　1、使用LayoutManager可以实现ListView，GridView以及流式布局的列表效果。

　　2、自带ViewHolder来实现View的复用机制，再也不用ListView那样在getView()里自己写ViewHolder了。

　　3、通过setItemAnimator(ItemAnimator animator)可以实现增删动画。

缺点

　　1、在RecyclerView中，没有一个onItemClickListener方法。

　　2、控制item的间隔，可以使用addItemDecoration(ItemDecoration decor)，不过里边的ItemDecoration是一个抽象类，需要自己去实现。

五、RecyclerView的使用

先看一下效果图，在看代码

   

1、在Activity中的代码

RecyclerView rvShow = (RecyclerView) findViewById(R.id.rvShow);
//设置布局管理器
rvShow.setLayoutManager(new LinearLayoutManager(activity));
//添加分割线
rvShow.addItemDecoration(new DividerListItemDecoration(activity,
        DividerListItemDecoration.VERTICAL_LIST));
//设置Item增加、移除动画
rvShow.setItemAnimator(new DefaultItemAnimator());
//使用此设置，以提高性能
rvShow.setHasFixedSize(true);
//设置适配器
mAdapter = new ListViewAdapter(activity, mDatas, R.layout.item_list_view);
mAdapter.setOnItemClickLitener(mListener);//设置点击监听器
rvShow.setAdapter(mAdapter);

2、定义一个点击的接口类

public interface OnRecyclerItemClickListener {
    void onItemClick(View view, int position);

    void onItemLongClick(View view, int position);
}

3、适配器与ListView的Adapter差不多，稍有不同

public class ListViewAdapter extends RecyclerView.Adapter<ListViewAdapter.MyViewHolder> {

    private Context context;

    private List<String> mDatas;

    private int layoutRes;

    private OnRecyclerItemClickListener mOnItemClickListener;

    public void setOnItemClickLitener(OnRecyclerItemClickListener mOnItemClickListener) {
        this.mOnItemClickListener = mOnItemClickListener;
    }

    public ListViewAdapter(Context context, List<String> mDatas, int layoutRes) {
        this.context = context;
        this.mDatas = mDatas;
        this.layoutRes = layoutRes;
    }

    @Override
    public int getItemViewType(int position) {
        //是用来根据position的不同来实现RecyclerView中对不同布局的要求
        return super.getItemViewType(position);
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(context).inflate(layoutRes, parent, false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(final MyViewHolder holder, int position) {
        holder.tv.setText(mDatas.get(position));
        // 如果设置了回调，则设置点击事件
        if (mOnItemClickListener != null) {
            holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    mOnItemClickListener.onItemClick(holder.itemView, holder.getAdapterPosition());
                }
            });

            holder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
                @Override
                public boolean onLongClick(View v) {
                    mOnItemClickListener.onItemLongClick(holder.itemView, holder.getAdapterPosition());
                    return false;
                }
            });
        }
    }

    @Override
    public int getItemCount() {
        return mDatas.size();
    }

    class MyViewHolder extends RecyclerView.ViewHolder {
        TextView tv;

        public MyViewHolder(View view) {
            super(view);
            tv = (TextView) view.findViewById(R.id.tvItem);
        }
    }
}

4、分割线的添加，继承ItemDecoration

public class DividerListItemDecoration 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 DividerListItemDecoration(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);
            android.support.v7.widget.RecyclerView v = new android.support.v7.widget.RecyclerView(parent.getContext());
            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);
        }
    }
}

5、实现不同的效果

表格样式代码，修改LayoutManager即可，其他类似

rvShow.setLayoutManager(new GridLayoutManager(activity, 4));// 第二参数4代表4列rvShow.addItemDecoration(new DividerGridItemDecoration(activity, false));

表格分割线

public 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, State state) {

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

    }

    private int getSpanCount(RecyclerView parent) {
        // 列数
        int spanCount = -1;
        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) {
        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) {
        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());
        }
    }
}

瀑布流布局

rvShow.setLayoutManager(new StaggeredGridLayoutManager(5, StaggeredGridLayoutManager.HORIZONTAL));// 第一个是网格的列数，第二个参数是数据呈现的方向
rvShow.addItemDecoration(new DividerGridItemDecoration(activity, false));

源码送上：https://github.com/PearLemon/RecyclerViewDemo