Xcode: Using custom fonts inside Dynamic framework

Swift 4:

This is maybe an old thread but has updated @xaphod for swift 4 as all static and global variables are lazily initialised using dispatch_once.

extension UIFont {

// load framework font in application
public static let loadAllFonts: () = {
    registerFontWith(filenameString: "SanFranciscoText-Regular.otf", bundleIdentifierString: "Fonts")
    registerFontWith(filenameString: "SanFranciscoText-Medium.otf", bundleIdentifierString: "Fonts")
    registerFontWith(filenameString: "SanFranciscoText-Semibold.otf", bundleIdentifierString: "Fonts")
    registerFontWith(filenameString: "SanFranciscoText-Bold.otf", bundleIdentifierString: "Fonts")
    registerFontWith(filenameString: "SanFranciscoText-LightItalic.otf", bundleIdentifierString: "Fonts")
}()

//MARK: - Make custom font bundle register to framework
static func registerFontWith(filenameString: String, bundleIdentifierString: String) {
    let frameworkBundle = Bundle(for: MSAlertController.self)
    let resourceBundleURL = frameworkBundle.url(forResource: bundleIdentifierString, withExtension: "bundle")
    if let url = resourceBundleURL, let bundle = Bundle(url: url) {
        let pathForResourceString = bundle.path(forResource: filenameString, ofType: nil)
        if let fontData = NSData(contentsOfFile: pathForResourceString!), let dataProvider = CGDataProvider.init(data: fontData) {
            let fontRef = CGFont.init(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.")
    }
}
}

Then you can call UIFont.loadAllfont inside the appDelegate

Here's my version of John's answer, showing how to call the function if you have lots of fonts

import Foundation

extension UIFont {

    @nonobjc static var loadAllFontsDO: dispatch_once_t = 0

    class func initialsAvatarFont() -> UIFont {
        loadAllFonts()
        if let retval = UIFont(name: "MyFontName", size: kInitialsAvatarFontSize) {
            return retval;
        } else {
            return UIFont.systemFontOfSize(kInitialsAvatarFontSize)
        }
    }

    class func loadAllFonts() {
        dispatch_once(&loadAllFontsDO) { () -> Void in
            registerFontWithFilenameString("thefontfilename.ttf", bundleIdentifierString: "nameOfResourceBundleAlongsideTheFrameworkBundle")
            // Add more font files here as required
        }
    }

    static func registerFontWithFilenameString(filenameString: String, bundleIdentifierString: String) {
        let frameworkBundle = NSBundle(forClass: AnyClassInYourFramework.self)
        let resourceBundleURL = frameworkBundle.URLForResource(bundleIdentifierString, withExtension: "bundle")
        if let bundle = NSBundle(URL: resourceBundleURL!) {
            let pathForResourceString = bundle.pathForResource(filenameString, ofType: nil)
            let fontData = NSData(contentsOfFile: pathForResourceString!)
            let dataProvider = CGDataProviderCreateWithCFData(fontData)
            let fontRef = CGFontCreateWithDataProvider(dataProvider)
            var errorRef: Unmanaged<CFError>? = nil

            if (CTFontManagerRegisterGraphicsFont(fontRef!, &errorRef) == false) {
                NSLog("Failed to register font - register graphics font failed - this font may have already been registered in the main bundle.")
            }
        }
        else {
            NSLog("Failed to register font - bundle identifier invalid.")
        }
    }
}

I'm here a bit late, but I took PetahChristian's solution and created a Swift version in the form of an extension. This is working for me. I've found that when you try to get a font using a font name and a size using the regular way that it always looks in the main bundle for the font file, and there's no method that takes a bundle identifier as a parameter. It would be nice if Apple would make one.

Swift:

public extension UIFont {

    public static func jbs_registerFont(withFilenameString filenameString: String, bundle: Bundle) {

        guard let pathForResourceString = bundle.path(forResource: filenameString, ofType: nil) else {
            print("UIFont+:  Failed to register font - path for resource not found.")
            return
        }

        guard let fontData = NSData(contentsOfFile: pathForResourceString) else {
            print("UIFont+:  Failed to register font - font data could not be loaded.")
            return
        }

        guard let dataProvider = CGDataProvider(data: fontData) else {
            print("UIFont+:  Failed to register font - data provider could not be loaded.")
            return
        }

        guard let font = CGFont(dataProvider) else {
            print("UIFont+:  Failed to register font - font could not be loaded.")
            return
        }

        var errorRef: Unmanaged<CFError>? = nil
        if (CTFontManagerRegisterGraphicsFont(font, &errorRef) == false) {
            print("UIFont+:  Failed to register font - register graphics font failed - this font may have already been registered in the main bundle.")
        }
    }

}

Usage Example:

UIFont.jbs_registerFont(
    withFilenameString: "Boogaloo-Regular.ttf",
    bundle: Bundle(identifier: "com.JBS.JBSFramework")!
)