Draw shadow only from 3 sides of UIView

问题:

I've successfully implemented drawing a shadow around my UIView like this:

block1.layer.masksToBounds = NO;
block1.layer.shadowOffset = CGSizeMake(0, 0);
block1.layer.shadowRadius = 1;
block1.layer.shadowOpacity = 0.7;

What now happens is I have a rectangular UIView and i would like to draw the shadow around it three sides, leaving the bottom side of it without the shadow.

I know that I have to specify the block1.layer.shadowPath by creating a new UIBezierPath but I'm not sure how to do it.

Obviously, setting layer.shadowOffset won't do the trick for me.

Thanks in advance!

回答1:

I know you say setting layer.shadowOffset won't work for you, but you are allowed to put in negative values so setting it layer.shadowOffset = CGSizeMake(0.0, -2.0) would come close to the effect you're looking for but of course I expect you want it to be even on the three sides.

So here we go with layer.shadowPath!

UIView *block1 = [[UIView alloc] initWithFrame:CGRectMake(32.0, 32.0, 128.0, 128.0)];
[block1 setBackgroundColor:[UIColor orangeColor]];
[self.view addSubview:block1];

block1.layer.masksToBounds = NO;
block1.layer.shadowOffset = CGSizeMake(0, 0);
block1.layer.shadowRadius = 1;
block1.layer.shadowOpacity = 0.7;

UIBezierPath *path = [UIBezierPath bezierPath];

// Start at the Top Left Corner
[path moveToPoint:CGPointMake(0.0, 0.0)];

// Move to the Top Right Corner
[path addLineToPoint:CGPointMake(CGRectGetWidth(block1.frame), 0.0)];

// Move to the Bottom Right Corner
[path addLineToPoint:CGPointMake(CGRectGetWidth(block1.frame), CGRectGetHeight(block1.frame))];

// This is the extra point in the middle :) Its the secret sauce.
[path addLineToPoint:CGPointMake(CGRectGetWidth(block1.frame) / 2.0, CGRectGetHeight(block1.frame) / 2.0)];

// Move to the Bottom Left Corner
[path addLineToPoint:CGPointMake(0.0, CGRectGetHeight(block1.frame))];

// Move to the Close the Path
[path closePath];

block1.layer.shadowPath = path.CGPath;

And to give you an idea of whats going on, here is the actual shadow path you just drew :)

Its possible to just shift that extra middle point before or after the other lines to choose which side will be omitted.

回答2:

A bit of improvement for other answers, thanks to Ashok R for swift code.

Since we were creating a triangular view in the background of the view with shadow on all sides, and a white triangle on the sides shadow is not needed.

It breaks in case of views with width comparatively larger than height.

A workaround will be to shift the path for the line where shadow is not needed a bit towards that side of view, instead of creating the triangular view Path completely.

I have created an extension for that -

extension UIView {
    func addshadow(top: Bool,
                   left: Bool,
                   bottom: Bool,
                   right: Bool,
                   shadowRadius: CGFloat = 2.0) {

        self.layer.masksToBounds = false
        self.layer.shadowOffset = CGSize(width: 0.0, height: 0.0)
        self.layer.shadowRadius = shadowRadius
        self.layer.shadowOpacity = 1.0

        let path = UIBezierPath()
        var x: CGFloat = 0
        var y: CGFloat = 0
        var viewWidth = self.frame.width
        var viewHeight = self.frame.height

        // here x, y, viewWidth, and viewHeight can be changed in
        // order to play around with the shadow paths.
        if (!top) {
            y+=(shadowRadius+1)
        }
        if (!bottom) {
            viewHeight-=(shadowRadius+1)
        }
        if (!left) {
            x+=(shadowRadius+1)
        }
        if (!right) {
            viewWidth-=(shadowRadius+1)
        }
        // selecting top most point
        path.move(to: CGPoint(x: x, y: y))
        // Move to the Bottom Left Corner, this will cover left edges
        /*
         |☐
         */
        path.addLine(to: CGPoint(x: x, y: viewHeight))
        // Move to the Bottom Right Corner, this will cover bottom edge
        /*
         ☐
         -
         */
        path.addLine(to: CGPoint(x: viewWidth, y: viewHeight))
        // Move to the Top Right Corner, this will cover right edge
        /*
         ☐|
         */
        path.addLine(to: CGPoint(x: viewWidth, y: y))
        // Move back to the initial point, this will cover the top edge
        /*
         _
         ☐
         */        
        path.close()
        self.layer.shadowPath = path.cgPath
    }

and set the boolean true for whichever side you want the shadow to appear

myView.addshadow(top: false, left: true, bottom: true, right: true, shadowRadius: 2.0)

// shadow radius is optional above and is set as default at 2.0

or myView.addshadow(top: true, left: true, bottom: true, right: true, shadowRadius: 2.0)

or myView.addshadow(top: false, left: false, bottom: true, right: true, shadowRadius: 2.0)

回答3:

Updating Ryan Poolos Answer to Swift 3.0

Thanks to Ryan Poolos

class sampleViewController: UIViewController {
    var block1: UIView! = nil

    override func viewDidLoad() {

        super.viewDidLoad()
        block1 = UIView(frame: CGRect(x: 32.0, y: 32.0, width: 128.0, height: 128.0))
        block1.backgroundColor = UIColor.orange
        self.view.addSubview(block1)

        block1.layer.masksToBounds = false
        block1.layer.shadowOffset = CGSize(width: 0.0, height: 0.0)
        block1.layer.shadowRadius = 1.0
        block1.layer.shadowOpacity = 0.7

        let path = UIBezierPath()

        // Start at the Top Left Corner
        path.move(to: CGPoint(x: 0.0, y: 0.0))

        // Move to the Top Right Corner
        path.addLine(to: CGPoint(x: block1.frame.size.width, y: 0.0))

        // Move to the Bottom Right Corner
        path.addLine(to: CGPoint(x: block1.frame.size.width, y: block1.frame.size.height))

        // This is the extra point in the middle :) Its the secret sauce.
        path.addLine(to: CGPoint(x: block1.frame.size.width/2.0, y: block1.frame.size.height/2.0))

        // Move to the Bottom Left Corner
        path.addLine(to: CGPoint(x: 0.0, y: block1.frame.size.height))

        path.close()

        block1.layer.shadowPath = path.cgPath
    }
}

Result:

回答4:

Try this

extension CALayer {
func applySketchShadow(color: UIColor, alpha: CGFloat, x: CGFloat, y: CGFloat, blur: CGFloat, spread: CGFloat)
{
    shadowColor = color.cgColor
    shadowOpacity = alpha
    shadowOffset = CGSize(width: x, height: y)
    shadowRadius = blur / 2.0
    if spread == 0 {
        shadowPath = nil
    } else {
        let dx = -spread
        let rect = bounds.insetBy(dx: dx, dy: dx)
        shadowPath = UIBezierPath(rect: rect).cgPath
    }
}