A UIFont extension in swift to load fonts from within a bundle

UIFontExtensions.swift

import UIKit

public extension UIFont {
    
    class func loadAllFonts(bundleIdentifierString: String) {
        registerFontWithFilenameString(filenameString: "icon-font.ttf", bundleIdentifierString: bundleIdentifierString)
        // Add more font files here as required
    }
    
    static func registerFontWithFilenameString(filenameString: String, bundleIdentifierString: String) {
        if let frameworkBundle = Bundle(identifier: bundleIdentifierString) {
            let pathForResourceString = frameworkBundle.path(forResource: filenameString, ofType: nil)
            let fontData = NSData(contentsOfFile: pathForResourceString!)
            let dataProvider = CGDataProvider(data: fontData!)
            let fontRef = CGFont(dataProvider!)
            var errorRef: Unmanaged<CFError>? = nil
            
            if (CTFontManagerRegisterGraphicsFont(fontRef, &errorRef) == false) {
                print("Failed to register font - register graphics font failed - this font may have already been registered in the main bundle.")
            }
        }
        else {
            print("Failed to register font - bundle identifier invalid.")
        }
    }
}

NOTE: The loadAllFonts(bundleIdentifierString:) method should only be called once. I'd wrap all the registerFontWithFilenamesString callse in a dispatch_once method but Swift3 doesn't have it anymore.

Possibly use this stackoverflow answer to extend DispatchQueue to add a DispatchQueue.once

You can add helper methods to this class to make it easier to get your fonts:

class func iconFont(size fontSize: CGFloat) -> UIFont {
        if let retval = UIFont(name: "icon-font", size: fontSize) {
            return retval;
        } else {
            return UIFont.systemFont(ofSize: fontSize)
        }
    }