ios 给UIImageView添加阴影

_borderView.layer.shadowColor = [UIColor grayColor].CGColor;
_borderView.layer.shadowOffset = CGSizeZero; _borderView.layer.shadowOpacity = 1.0;
_borderView.layer.shadowRadius = 2;
_borderView.backgroundColor = [UIColor whiteColor];
_borderView.clipsToBounds = NO;