设置圆角+阴影

使用双层 View 实现； 

   self.signInView.backgroundColor = [UIColor clearColor];  // 底层 view 设置阴影，要设置透明

        [self.headerBgImgView addSubview:self.signInView];

        [self.signInView mas_makeConstraints:^(MASConstraintMaker *make) {

            make.right.mas_equalTo(self);

            make.top.mas_equalTo(self.userHeadBtn.mas_top);

            make.width.mas_equalTo(AUTO_RATIO(74.f));

            make.height.mas_equalTo(AUTO_RATIO(28.f));

        }];

    [self layoutIfNeeded];

    UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:self.signInView.bounds byRoundingCorners:UIRectCornerBottomLeft | UIRectCornerTopLeft cornerRadii:CGSizeMake(AUTO_RATIO(14), AUTO_RATIO(14))];

    self.signInView.layer.shadowColor = [UIColor blackColor].CGColor;

    self.signInView.layer.shadowOffset = CGSizeMake(0, 2); // 阴影偏移量，默认（0,0）

    self.signInView.layer.shadowOpacity = 1;

    self.signInView.layer.shadowRadius = 8.0;

    self.signInView.layer.shadowPath = maskPath.CGPath;

    self.signInView.layer.masksToBounds = NO;

    [self.signInBtn mas_makeConstraints:^(MASConstraintMaker *make) {

        make.edges.mas_equalTo(self.signInView);

    }];

    [self layoutIfNeeded];

    CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];

    //设置大小

    maskLayer.frame = self.signInBtn.bounds;

    //设置图形样子

    maskLayer.path = maskPath.CGPath;

    self.signInBtn.layer.mask = maskLayer;