给圆角图片加阴影

让UIView圆角显示很简单，只需要三行代码

CALayer * layer = [avatarImageView layer];

[layer setMasksToBounds:YES];

[layer setCornerRadius:9.0];

但是，如给给圆角view加阴影，传统加阴影的方法是不行的，

传统的方法就是：

avatarImageView.layer.shadowColor = [UIColor blackColor].CGColor;

avatarImageView.layer.shadowOffset = CGSizeMake(0, 1);

avatarImageView.layer.shadowOpacity = 1;

因为setMasksToBounds表示对frame外的内容进行了裁减，只可显示frame内的内容。由于这种方法加的阴影在frame外，所以被裁减了。

传统方法不行，那我们可以把圆角的avatarImageView放到一个大小与它一样的的UIView中，让这个view有阴影，那效果看起来就一样了。

CGRect rect;

rect = CGRectMake(0, 0, 48, 48);

avatarImageView = [[UIImageView alloc] initWithFrame:rect];

avatarImageView.image = [UIImage imageNamed:@"test.png"];

//Round the corners

CALayer * layer = [avatarImageView layer];

[layer setMasksToBounds:YES];

[layer setCornerRadius:9.0];

//Add a shadow by wrapping the avatar into a container

UIView * shadow = [[UIView alloc] initWithFrame: rect];

avatarImageView.frame = CGRectMake(0,0,rect.size.width, rect.size.height);

// setup shadow layer and corner

shadow.layer.shadowColor = [UIColor grayColor].CGColor;

shadow.layer.shadowOffset = CGSizeMake(0, 1);

shadow.layer.shadowOpacity = 1;

shadow.layer.shadowRadius = 9.0;

shadow.layer.cornerRadius = 9.0;

shadow.clipsToBounds = NO;

// combine the views

[shadow addSubview: avatarImageView];