How to generate an UIImage from custom text in Swift

Question

I am trying to generate an UIImage from custom text in Swift3.

Using iOS Controls, It's possible to create an UIImage, below is the code:

class func imageWithText(txtField: UITextField) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(txtField.bounds.size, false, 0.0)
        txtField.layer.render(in: UIGraphicsGetCurrentContext()!)
        let img = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return img!
    }

Note: I know it's also possible to add some text to an image, but I don't want to do like this.

Can someone help me to resolve this? Thank you!

Answer 1

Here is a String extension that can be used as shown below to create UIImage instances from a String instance, without the need for UI controls like UITextField or UILabel as requested in the original question:

var image: UIImage? =
    "Test".image(withAttributes: [
        .foregroundColor: UIColor.red,
        .font: UIFont.systemFont(ofSize: 30.0),
    ], size: CGSize(width: 300.0, height: 80.0))

// Or
image = "Test".image(withAttributes: [.font: UIFont.systemFont(ofSize: 80.0)])

// Or
image = "Test".image(size: CGSize(width: 300.0, height: 80.0))

// Or even just
image = "Test".image()

Below are two possible implementations for achieving the desired effect demonstrated above:

UIGraphicsImageRenderer Method (more performant and recommended implementation by Apple)

extension String {
    
    /// Generates a `UIImage` instance from this string using a specified
    /// attributes and size.
    ///
    /// - Parameters:
    ///     - attributes: to draw this string with. Default is `nil`.
    ///     - size: of the image to return.
    /// - Returns: a `UIImage` instance from this string using a specified
    /// attributes and size, or `nil` if the operation fails.
    func image(withAttributes attributes: [NSAttributedString.Key: Any]? = nil, size: CGSize? = nil) -> UIImage? {
        let size = size ?? (self as NSString).size(withAttributes: attributes)
        return UIGraphicsImageRenderer(size: size).image { _ in
            (self as NSString).draw(in: CGRect(origin: .zero, size: size),
                                    withAttributes: attributes)
        }
    }
    
}

UIGraphicsImageContext Method (old-school; included for thoroughness)

extension String {
    
    /// Generates a `UIImage` instance from this string using a specified
    /// attributes and size.
    ///
    /// - Parameters:
    ///     - attributes: to draw this string with. Default is `nil`.
    ///     - size: of the image to return.
    /// - Returns: a `UIImage` instance from this string using a specified
    /// attributes and size, or `nil` if the operation fails.
    func image(withAttributes attributes: [NSAttributedString.Key: Any]? = nil, size: CGSize? = nil) -> UIImage? {
        let size = size ?? (self as NSString).size(withAttributes: attributes)
        UIGraphicsBeginImageContext(size)
        (self as NSString).draw(in: CGRect(origin: .zero, size: size), 
                                withAttributes: attributes)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
    
}