Create UIImage Programmatically in Swift 4

December 20, 2018 ยท 2 minute read

Create UIImage Programmatically Swift 4

Learning to unit test and need to work with images, here’s how to create a UIImage from scratch. Just determine what color or size you need and add this extension to your class.

public extension UIImage
{
    public convenience init?(color: UIColor, size: CGSize = CGSize(width: 1, height: 1))
    {
        let rect = CGRect(origin: .zero, size: size)
        
        UIGraphicsBeginImageContextWithOptions(rect.size, false, 0.0)
        color.setFill()
        UIRectFill(rect)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        guard let cgImage = image?.cgImage else { return nil }
        self.init(cgImage: cgImage)
    }
}

/*
Now you can create an image with a just a custom color:

 let redImage = UIImage(color: .red)
 
 **** OR ****
 
 Create one with a custom size and color:
 
 let redImage200x200 = UIImage(color: .red, size: CGSize(width: 200, height: 200)
*/

Or if you just want it to be a method, use the following:


func createAnImageOf(size: CGSize, color: UIColor) -> UIImage?
{
	let rect = CGRect(origin: .zero, size: size)
	
	UIGraphicsBeginImageContextWithOptions(rect.size, false, 0.0)
	color.setFill()
	
	let image = UIGraphicsGetImageFromCurrentImageContext()
	UIGraphicsEndImageContext()
	
	return image
}

And as a bonus, you can rescale all your images that come in to a preset maximum width (if you want height, I’m sure you can figure it out with this snippet as a head start):

func scaleImage(image: UIImage, maximumWidth: CGFloat) -> UIImage
{
	let rect: CGRect = CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height)
	let cgImage: CGImage = image.cgImage!.cropping(to: rect)!
	
	return UIImage(cgImage: cgImage, scale: image.size.width / maximumWidth, orientation: image.imageOrientation)
}

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