Grid RecyclerView.ItemDecoration

/**
 * @author zhy
 */
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 = ContextCompat.getDrawable(context, R.drawable.divider_present);
      //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) {
         // 如果是最后一行，则不需要绘制底部
         if (pos + spanCount >= childCount)
            return true;
      } else if (layoutManager instanceof StaggeredGridLayoutManager) {
         int orientation = ((StaggeredGridLayoutManager) layoutManager)
               .getOrientation();
         // StaggeredGridLayoutManager 且纵向滚动
         if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            // 如果是最后一行，则不需要绘制底部
            if (pos + spanCount >= 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();
      // 如果是最后一行，则不需要绘制底部
      if (isLastRaw(parent, itemPosition, spanCount, childCount)) {
         // 最后一行且为最后一列则不绘制
         if (isLastColum(parent, itemPosition, spanCount, childCount)) {
            outRect.set(0, 0, 0, 0);
         } else {
            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());
      }
   }
}