iOS侧面加shadow

UIBezierPath *shadowPath = [UIBezierPath bezierPathWithRect:_bgView.bounds];
        _bgView.layer.masksToBounds = NO;
        _bgView.layer.shadowColor = [UIColor blackColor].CGColor;
        _bgView.layer.shadowOffset = CGSizeMake(0.0f, 0.0f);
        _bgView.layer.shadowOpacity = 1.0f;
        _bgView.layer.shadowRadius = 2.5f;
        _bgView.layer.shadowPath = shadowPath.CGPath;