Shadow UIview and clipsToBounds

问题

I would like to set the shadow to my container UIView. I use this code to make it:

- (id)initWithCoder:(NSCoder*)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if (self) {

        //-> drop shadow
        [self.layer setShadowColor:[UIColor blackColor].CGColor];
        [self.layer setShadowOpacity:0.6];
        [self.layer setShadowRadius:2.0];
        [self.layer setShadowOffset:CGSizeMake(2.0, 2.0)];
    }

    return self;
}

This works well. But, when I use _containerView.clipsToBounds = YES; on this container UIView, I can't see my shadow. Why?

回答1:

the clipsToBounds also clips your shadow. In order to prevent this you can add _containerView.layer.masksToBounds = NO which disables clipping of sublayers (see more here).

回答2:

Here is the UIView extension.

extension UIView {
    func addShadowAndRoundCorner(cornerRadius : CGFloat) {
        self.layer.shadowOffset = .zero
        self.layer.shadowOpacity = 0.5
        self.layer.shadowRadius = 3
        self.layer.shadowColor = UIColor.black.cgColor
        self.layer.masksToBounds = false
        self.layer.cornerRadius = cornerRadius
    }
}

Call this function after creation of view as follows:

let roundView = UIView()
roundView.frame = CGRect.init(x: 0, y: 0, width: 100, height: 100)
roundView.addShadowAndRoundCorner(cornerRadius: 100/2)

回答3:

- (void)layoutSubviews
{
    [super layoutSubviews];

    CAGradientLayer *l = [CAGradientLayer layer];
    l.frame = self.bounds;
    l.colors = [NSArray arrayWithObjects:(id)[UIColor clearColor].CGColor, (id)[UIColor whiteColor].CGColor, (id)[UIColor whiteColor].CGColor,(id)[UIColor whiteColor].CGColor,(id)[UIColor whiteColor].CGColor,(id)[UIColor whiteColor].CGColor, (id)[UIColor clearColor].CGColor,(id)[UIColor clearColor].CGColor, nil];
    l.startPoint = CGPointMake(0.0f, 1.0f);
    l.endPoint = CGPointMake(1.0f, 1.0f);
    self.layer.mask = l;
}

来源：https://stackoverflow.com/questions/23760918/shadow-uiview-and-clipstobounds