参考文章：https://zhuanlan.zhihu.com/p/269559400
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
// 圆角角度
CGFloat radius = 10.f;
// 设置cell 背景色为透明
cell.backgroundColor = [UIColor clearColor];
// 创建两个layer
CAShapeLayer *normalLayer = [[CAShapeLayer alloc] init];
CAShapeLayer *selectLayer = [[CAShapeLayer alloc] init];
// 获取显示区域大小
CGRect bounds = CGRectInset(cell.bounds, 10, 0);
// cell的backgroundView
UIView *normalBgView = [[UIView alloc] initWithFrame:bounds];
// 获取每组行数
NSInteger rowNum = [tableView numberOfRowsInSection:indexPath.section];
// 贝塞尔曲线
UIBezierPath *bezierPath = nil;
if (rowNum == 1) {
// 一组只有一行（四个角全部为圆角）
bezierPath = [UIBezierPath bezierPathWithRoundedRect:bounds byRoundingCorners:UIRectCornerAllCorners cornerRadii:CGSizeMake(radius, radius)];
normalBgView.clipsToBounds = NO;
} else {
normalBgView.clipsToBounds = YES;
if (indexPath.row == 0) {
normalBgView.frame = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(-5, 0, 0, 0));
CGRect rect = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(5, 0, 0, 0));
// 每组第一行（添加左上和右上的圆角）
bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:(UIRectCornerTopLeft|UIRectCornerTopRight) cornerRadii:CGSizeMake(radius, radius)];
} else if (indexPath.row == rowNum - 1) {
normalBgView.frame = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(0, 0, -5, 0));
CGRect rect = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(0, 0, 5, 0));
// 每组最后一行（添加左下和右下的圆角）
bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:(UIRectCornerBottomLeft|UIRectCornerBottomRight) cornerRadii:CGSizeMake(radius, radius)];
} else {
// 每组不是首位的行不设置圆角
bezierPath = [UIBezierPath bezierPathWithRect:bounds];
}
}
// 阴影
normalLayer.shadowColor = [UIColor blackColor].CGColor;
normalLayer.shadowOpacity = 0.3;
normalLayer.shadowOffset = CGSizeMake(0, 0);
normalLayer.path = bezierPath.CGPath;
normalLayer.shadowPath = bezierPath.CGPath;
// 把已经绘制好的贝塞尔曲线路径赋值给图层，然后图层根据path进行图像渲染render
normalLayer.path = bezierPath.CGPath;
selectLayer.path = bezierPath.CGPath;
// 设置填充颜色
normalLayer.fillColor = [UIColor whiteColor].CGColor;
// 添加图层到nomarBgView中
[normalBgView.layer insertSublayer:normalLayer atIndex:0];
normalBgView.backgroundColor = UIColor.clearColor;
cell.backgroundView = normalBgView;
// 替换cell点击效果
UIView *selectBgView = [[UIView alloc] initWithFrame:bounds];
selectLayer.fillColor = [UIColor colorWithWhite:0.95 alpha:1.0].CGColor;
[selectBgView.layer insertSublayer:selectLayer atIndex:0];
selectBgView.backgroundColor = UIColor.clearColor;
cell.selectedBackgroundView = selectBgView;
}
备注（去了这里没发现区别，iOS 14 上， 其它未验证）
// 替换cell点击效果
UIView *selectBgView = [[UIView alloc] initWithFrame:bounds];
selectLayer.fillColor = [UIColor colorWithWhite:0.95 alpha:1.0].CGColor;
[selectBgView.layer insertSublayer:selectLayer atIndex:0];
selectBgView.backgroundColor = UIColor.clearColor;
cell.selectedBackgroundView = selectBgView;