code: public void setShadow(Drawable shadow, int edgeFlag) {
          if ((edgeFlag & EDGE_LEFT) != 0) {
              mShadowLeft = shadow;
          } else if ((edgeFlag & EDGE_RIGHT) != 0) {
              mShadowRight = shadow;
          } else if ((edgeFlag & EDGE_BOTTOM) != 0) {
              mShadowBottom = shadow;
          }
          invalidate();
      }
docs: Set a drawable used for edge shadow.
  
  @param shadow    Drawable to use
  @param edgeFlags Combination of edge flags describing the edge to set
  @see #EDGE_LEFT
  @see #EDGE_RIGHT
  @see #EDGE_BOTTOM