UIView加阴影效果

_imageView.layer.shadowColor = [UIColor blackColor].CGColor;
//shadowColor阴影颜色  
 _imageView.layer.shadowOffset = CGSizeMake(4,4);
//shadowOffset阴影偏移,x向右偏移4，y向下偏移4，默认(0, -3),这个跟shadowRadius配合使用  
_imageView.layer.shadowOpacity = 0.8;
//阴影透明度，默认0      
_imageView.layer.shadowRadius = 4;
//阴影半径，默认3 

UIBezierPath path路径

参考
http://blog.csdn.net/rhljiayou/article/details/10178723