Use Storyboard to mask UIView and give rounded corners?

Yes, I use that a lot but question like this was already answered many times.

But anyway in Interface Builder. You need to add User Defined Runtime Attributes like this:

layer.masksToBounds Boolean YES
layer.cornerRadius Number {View's Width/2}

https://i.imgur.com/N7gNLwe.png

and enable

Clips subviews

https://i.imgur.com/6DA6qjb.png

Results:

https://i.stack.imgur.com/7zbNW.png

You can do it in a storyboard by using user-defined properties. Select the view that you want to round and open its Identity Inspector. In the User Defined Runtime Attributes section, add the following two entries:

Key Path: layer.cornerRadius, Type: Number, Value: (whatever radius you want)

Key Path: layer.masksToBounds, Type: Boolean, Value: checked

You may have to import QuartzKit in your view's corresponding class file (if any), but I swear that I've gotten it to work without doing that. Your results may vary.

EDIT: Example of a dynamic radius

extension UIView {

    /// The ratio (from 0.0 to 1.0, inclusive) of the view's corner radius
    /// to its width. For example, a 50% radius would be specified with
    /// `cornerRadiusRatio = 0.5`.
    @IBDesignable public var cornerRadiusRatio: CGFloat {
        get {
            return layer.cornerRadius / frame.width
        }

        set {
            // Make sure that it's between 0.0 and 1.0. If not, restrict it
            // to that range.
            let normalizedRatio = max(0.0, min(1.0, newValue))
            layer.cornerRadius = frame.width * normalizedRatio
        }
    }

}

I verified that this works in a playground.

Use IBInspectable to add the properties to the Storyboard:

https://i.stack.imgur.com/dml4F.png

extension UIView {
    
    @IBInspectable var cornerRadiusV: CGFloat {
        get {
            return layer.cornerRadius
        }
        set {
            layer.cornerRadius = newValue
            layer.masksToBounds = newValue > 0
        }
    }
    
    @IBInspectable var borderWidthV: CGFloat {
        get {
            return layer.borderWidth
        }
        set {
            layer.borderWidth = newValue
        }
    }
    
    @IBInspectable var borderColorV: UIColor? {
        get {
            return UIColor(cgColor: layer.borderColor!)
        }
        set {
            layer.borderColor = newValue?.cgColor
        }
    }
}

Even after making all changes in storyboard, Woraphot's answer doesn't work for me.

This worked for me :

layer.cornerRadius = 10
layer.borderWidth = 1
layer.borderColor = UIColor.blue.cgColor

Long answer :

Rounded Corners of UIView/UIButton etc

customUIView.layer.cornerRadius = 10

Border Thickness

pcustomUIView.layer.borderWidth = 1

Border Color

customUIView.layer.borderColor = UIColor.blue.cgColor