RecycleView之GridLayoutItemDecoration等距分割线

1.自定义分割线

public class GridLayoutItemDecoration extends RecyclerView.ItemDecoration {

    private Drawable mDriver;

    // 网上绝大部分用的系统的一个属性 叫做 android.R.attrs.listDriver ，这个也可以，需要在清单文件中配置
    public GridLayoutItemDecoration(Context context, int drawableRescourseId) {
        // 解析获取 Drawable
        mDriver = ContextCompat.getDrawable(context, drawableRescourseId);
    }


    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        // 留出分割线的位置  每个item控件的下边和右边
        outRect.bottom = mDriver.getIntrinsicHeight();


        GridLayoutManager mgr;
        if (parent.getLayoutManager() instanceof GridLayoutManager) {
            mgr = (GridLayoutManager) parent.getLayoutManager();
        } else {
            return;
        }
        int position = parent.getChildAdapterPosition(view);

        if (position == RecyclerView.NO_POSITION) {
            // here I need to access the position of the current element
            // and call outRect.set(left, top , right, bottom);
            // which is not possible because it is no longer in the adapter
            return;
        }

        int spanCount = mgr.getSpanCount();
        int spanSize = mgr.getSpanSizeLookup().getSpanSize(position);
        int spanIndex = mgr.getSpanSizeLookup().getSpanIndex(position, spanCount);

        if (spanIndex == spanCount - 1) {
            // last element

            outRect.left = mDriver.getIntrinsicWidth() / 2;
            outRect.right = mDriver.getIntrinsicWidth();

        } else if (spanIndex == 0) {
            // first element
            outRect.left = mDriver.getIntrinsicWidth();
            outRect.right = mDriver.getIntrinsicWidth() / 2;

        } else {
            // middle element
            outRect.left = mDriver.getIntrinsicWidth()/2;
            outRect.right = mDriver.getIntrinsicWidth() / 2;
        }
    }

    // 绘制分割线
    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        // 绘制分割线

        // 绘制水平方向
        drawHorizontal(c, parent);
//         绘制垂直方向
        drawVertical(c, parent);
    }


    /**
     * 绘制垂直方向的分割线
     *
     * @param c
     * @param parent
     */
    private void drawVertical(Canvas c, RecyclerView parent) {
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View childView = parent.getChildAt(i);

            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) childView.getLayoutParams();

            int top = childView.getTop() - params.topMargin;
            int bottom = childView.getBottom() + params.bottomMargin;
            int left = childView.getRight() + params.rightMargin;
            int right = left + mDriver.getIntrinsicWidth();

            //计算水平分割线的位置
            mDriver.setBounds(left, top, right, bottom);
            mDriver.draw(c);
        }
    }


    /**
     * 绘制水平方向的分割线
     *
     * @param c
     * @param parent
     */
    private void drawHorizontal(Canvas c, RecyclerView parent) {
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View childView = parent.getChildAt(i);

            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) childView.getLayoutParams();

            int left = childView.getLeft() - params.leftMargin;
            int right = childView.getRight() + mDriver.getIntrinsicWidth() + params.rightMargin;
            int top = childView.getBottom() + params.bottomMargin;
            int bottom = top + mDriver.getIntrinsicHeight();

            //计算水平分割线的位置
            mDriver.setBounds(left, top, right, bottom);
            mDriver.draw(c);
        }
    }
}

创建分割线颜色和大小drawable\item_divider_white.xml