Converting a callback function to async await in Swift

Occasionally you will need to convert a callback based function to an async/await function. One example of this is below, calculating a map route appears to be only available as a callback based one. Below is an example of how to convert it to an async function. This code is actually used in Weather Driver.

func calculateSubRoute(route: MKRoute, step: MKRoute.Step) async throws -> MKDirections.Response? {
	return try await withCheckedThrowingContinuation { continuation in
		let request = MKDirections.Request()
		request.source = MKMapItem(placemark: MKPlacemark(coordinate: route.steps.first!.polyline.coordinate))
		request.destination = MKMapItem(placemark: MKPlacemark(coordinate: step.polyline.coordinate))
		request.requestsAlternateRoutes = true
		request.transportType = .automobile

		let directions = MKDirections(request: request)
		directions.calculate() { response, error in
			if error != nil {
				continuation.resume(throwing: error!)
			continuation.resume(returning: response)

Sharpening My Tools Part 2

Developing an iOS application is full of small bits of repetitive tasks. When you develop User Interface in code, you must create and handle constraints in code. Depending on what you have to do this could become extremely repetitive and complicated. You can write each constraint yourself, but this gets time consuming and could become messy and confusing.

I decided to create a function that accepts the child view and the parent LayoutGuide, this solved the issue for if you want the child to fill the parent. It however doesn’t solve all issues, example when you don’t want the bottom side to match the parent. Initially I decided to allow booleans to be passed in for each constraint to disable them and still allow them to be manual.

However this still left my code messy and complicated. So I decided to make it more inclusive of the other needs. In the next version I decided to allow up to 3 parameters for each of the side constraints, one named for the side to enable and disable it, a constant to allow a distance from the anchor, and a target for those times when it shouldn’t be pinned to the parent element.

However this wasn’t quite enough I needed two other capabilities. The first, one I needed the ability to enable and disable constraints inside of other classes. I return a class with they NSLayoutConstraint for each constraint allowing other classes to access these. The other major capability is the ability to have width and height anchor constraint, therefore I allow these constants to be passed in as parameters.

This utility class has cleaned up my code quite a bit, I hope others will find it useful. It is available on Github at

Sharpening My Tool Part 1

I’ve been working on a full fledged pdf reader application for iOS. During the process of developing for this I have wanted to use Icons from Font Awesome; as buttons in the app.

Apple’s iOS doesn’t like SVG files or the font awesome font files, to work around this I’ve decided to make a tool that will convert Font Awesome SVG files into image files that can then be used directly in the application.

The tool that I wrote is a command line tool that generates three image files that corresponds to the 1x, 2x, and 3x that apps require. However this isn’t quite enough to finish the process, in the normal process you must then create an imageset in xCode then drag in the images. We can automate this process by creating a specific directory structure and json files to tell xCode where the files are.

The source code of this script is available on GitHub. It can be modified for use with any SVG image set, I use it with both Font Awesome Free Version and Font Awesome Pro. The source can be downloaded from

Weather Driver

My current personal project is codenamed Weather Driver. This is an iOS application targeted at Truck Drivers and other people who travel on the road. This application will allow them to better plan their trip around the weather. You will be able to enter your destination, chose a route, and then see the weather at various points thru-out the route.

This uses WeatherKit API from Apple, along with MapKit. This will have a server side component to handle getting the weather from Apple. The server side portion of this application will be written in Node.js.

How I decided to build this application, I drove 18-wheel for about 3 years. Part of my job as a Truck Driver was to plan my route based on the weather, I always found it tedious to check both the route I had to travel and the weather at multiple locations along the route.

I’ve been thinking about this project for over a year and finally have the tools to build it. Follow me as I build this project out and bring it to market. @JJAllenTech