UIView with rounded corners and drop shadow?

Question

I’ve been working on an application for a couple of years and received a simple design request: Round the corners on a UIView and add a drop shadow.To do as given below.

I want a custom UIView... : I just wanted a blank white view with rounded corners and a light drop shadow (with no lighting effect). I can do each of those one by one but the usual clipToBounds/maskToBounds conflicts occur.

Answer 1

Swift

// corner radius
blueView.layer.cornerRadius = 10

// border
blueView.layer.borderWidth = 1.0
blueView.layer.borderColor = UIColor.black.cgColor

// shadow
blueView.layer.shadowColor = UIColor.black.cgColor
blueView.layer.shadowOffset = CGSize(width: 3, height: 3)
blueView.layer.shadowOpacity = 0.7
blueView.layer.shadowRadius = 4.0

Exploring the options

Problem 1: Shadow gets clipped off

What if there are sublayers or subviews (like an image) whose content we want to clip to the bounds of our view?

We can accomplish this with

blueView.layer.masksToBounds = true

(Alternatively, blueView.clipsToBounds = true gives the same result.)

But, oh no! The shadow was also clipped off because it's outside of the bounds! What to do? What to do?

Solution

Use separate views for the shadow and the border. The base view is transparent and has the shadow. The border view clips any other subcontent that it has to its borders.

// add the shadow to the base view
baseView.backgroundColor = UIColor.clear
baseView.layer.shadowColor = UIColor.black.cgColor
baseView.layer.shadowOffset = CGSize(width: 3, height: 3)
baseView.layer.shadowOpacity = 0.7
baseView.layer.shadowRadius = 4.0

// add the border to subview
let borderView = UIView()
borderView.frame = baseView.bounds
borderView.layer.cornerRadius = 10
borderView.layer.borderColor = UIColor.black.cgColor
borderView.layer.borderWidth = 1.0
borderView.layer.masksToBounds = true
baseView.addSubview(borderView)

// add any other subcontent that you want clipped
let otherSubContent = UIImageView()
otherSubContent.image = UIImage(named: "lion")
otherSubContent.frame = borderView.bounds
borderView.addSubview(otherSubContent)

This gives the following result:

Problem 2: Poor performance

Adding rounded corners and shadows can be a performance hit. You can improve performance by using a predefined path for the shadow and also specifying that it be rasterized. The following code can be added to the example above.

baseView.layer.shadowPath = UIBezierPath(roundedRect: baseView.bounds, cornerRadius: 10).cgPath
baseView.layer.shouldRasterize = true
baseView.layer.rasterizationScale = UIScreen.main.scale

See this post for more details. See here and here also.

This answer was tested with Swift 4 and Xcode 9.