实现方案

需求：视图既需要圆角，又需要阴影

实现重点：

• 不要使用clipToBounds
• 需要绘制一个圆角UIBezierPath。直接使用直接 UIBezierPath 会发现在四个角处的阴影会比较重
• 圆角UIBezierPath 的 cornerRadii 需要与button的圆角大小一样

- (void)makeRoundButtonShadow:(UIButton *)button {
    button.layer.cornerRadius = 8;
    [button addShadow:UIColor.blackColor shadowOpacity:0.15 shadowRadius:2 shadowOffset:CGSizeZero];
    CGRect rect = CGRectMake(0, 0, button.width, button.height);
    UIBezierPath *cornerPath = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:UIRectCornerAllCorners cornerRadii:CGSizeMake(8, 8)];
    button.layer.shadowPath = cornerPath.CGPath;
}

- (void)addShadow:(UIColor *)shadowColor
    shadowOpacity:(CGFloat)shadowOpacity
     shadowRadius:(CGFloat)shadowRadius
     shadowOffset:(CGSize)shadowOffset {
    self.layer.shadowColor = shadowColor.CGColor;
    self.layer.shadowOffset = shadowOffset;
    self.layer.shadowOpacity = shadowOpacity;
    self.layer.shadowRadius = shadowRadius;
}