code: private void initCorner() {
          switch (mCornerSide) {
              case CORNER_NONE:
                  mRightCorner = CORNER_NONE;
                  mLeftCorner = CORNER_NONE;
                  mBottomCorner = CORNER_NONE;
                  mTopCorner = CORNER_NONE;
                  break;
              case CORNER_LEFT:
                  // 只设定了左边角时，右边角为none
                  mRightCorner = CORNER_NONE;
                  mBottomCorner = CORNER_NONE;
                  mTopCorner = CORNER_NONE;
                  break;
              case CORNER_RIGHT:
                  // 只设定了右边角时，左边角为none
                  mLeftCorner = CORNER_NONE;
                  mBottomCorner = CORNER_NONE;
                  mTopCorner = CORNER_NONE;
                  break;
              case CORNER_LEFT_RIGHT:
                  mBottomCorner = CORNER_NONE;
                  mTopCorner = CORNER_NONE;
                  break;
              case CORNER_BOTTOM:
                  mLeftCorner = CORNER_NONE;
                  mRightCorner = CORNER_NONE;
                  mTopCorner = CORNER_NONE;
                  break;
              case CORNER_TOP:
                  mBottomCorner = CORNER_NONE;
                  mLeftCorner = CORNER_NONE;
                  mRightCorner = CORNER_NONE;
                  break;
          }
      }
docs: 初始化左右角设定