RecyclerView设置divider，需要自定义相关实现类：

public class DividerGridItemDecoration extends RecyclerView.ItemDecoration {

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

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

        this.spanCount = spanCount;
    }

    @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();
            if (i < spanCount) {
                int _top = child.getTop() + params.topMargin;
                mDivider.setBounds(left, _top, right, _top + mDivider.getIntrinsicHeight());
                mDivider.draw(c);
            }
            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();

            if (i % spanCount == 0) {
                int _left = child.getLeft() + params.leftMargin;
                mDivider.setBounds(_left, top, _left + mDivider.getIntrinsicWidth(), bottom);
                mDivider.draw(c);
            }
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
}

使用方式：

RecyclerView recyclerView = ...;
recyclerView.addItemDecoration(new DividerGridItemDecoration(this, 4));

最后，style里面还需要加入下面一行代码：

<item name="android:listDivider">@drawable/line_drawable</item>

line_deawable.xml代码如下：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle" >

    <solid android:color="@color/line_color"/>
    <size android:height="0.5dp" android:width="0.5dp"/>

</shape>