There's a good chance that you're using SwiftUI and that you're not quite sure how and when SwiftUI determines which views should redraw. And arguably, that's a good thing. SwiftUI is clearly smart enough to make decent decisions without any negative consequences. In fact, you might even have set up your app in a way that coincidentally plays into SwiftUI's strength beautifully. There's an equal likelihood that your setup isn't as performant as you might think but you're just not seeing any issues yet. Recently, I had to figure out how SwiftUI determines that it should redraw views in order...

The biggest features in Swift 5.5 all revolve around its new and improved concurrency features. There's actors, async/await, and more. With these features folks are wondering whether async/await will replace Combine eventually. While I overall do not think that async/await can or will replace Combine on its own, Swift 5.5 comes with some concurrency features that provide very similar functionality to Combine. If you're curious about my thoughts on Combine and async/await specifically, I still believe that what I wrote about this topic earlier is true. Async/await will be a great tool for work that have a clearly defined start...

Async/await will be the defacto way of doing asynchronous programming on iOS 15 and above. I've already written quite a bit about the new Swift Concurrency features, and there's still plenty to write about. In this post, I'm going to take a look at building an asynchronous image loader that has support for caching. SwiftUI on iOS 15 already has a component that allows us to load images from the network but it doesn't support caching (other than what’s already offered by URLSession), and it only works with a URL rather than also accepting a URLRequest. The component will be...

If you've worked with Combine in your applications you'll know what it means when I tell you that you should always retain your cancellables. Cancellables are an important part of working with Combine, similar to how disposables are an important part of working with RxSwift. Interestingly, Swift Concurrency's AsyncSequence operates without an equivalent to cancellable (with memory leaks as a result). That said, in this post we'll only focus on Combine. For example, you might have built a publisher that wraps CLLocationManagerDelegate and exposes the user's current location with a currentLocation publisher that's a CurrentValueSubject<CLLocation, Never>. Subscribing to this publisher...

One of my favorite concurrency problems to solve is building concurrency-proof token refresh flows. Refreshing authentication tokens is something that a lot of us deal with regularly, and doing it correctly can be a pretty challenging task. Especially when you want to make sure you only issue a single token refresh request even if multiple network calls encounter the need to refresh a token. Furthermore, you want to make sure that you automatically retry a request that failed due to a token expiration after you've obtained a new (valid) authentication token. I wrote about a flow that does this before,...

Earlier, I published a post on Swift Concurrency's task groups. If you haven't read that post yet, and you're not familiar with task groups, I recommend that you read that post first because I won't be explaining task groups in this post. Instead, you will learn about a technique that you can use to work around a limitation of task groups. Task groups can run a number of child tasks where every child task in the task group produces the same output. This is a hard requirement of the withTaskGroup function. This means that task groups are not the right...

In last week's post, I demonstrated how you can use a task group in Swift to concurrently run multiple tasks that produce the same output. This is useful when you're loading a bunch of images, or in any other case where you have a potentially undefined number of tasks to run, as long as you (somehow) make sure that every task in your group produces the same output. Unfortunately, this isn't always a reasonable thing to do. For example, you might already know that you only have a very limited, predetermined, number of tasks that you want to run. These...

With Apple's overhaul of how concurrency will work in Swift 5.5 and newer, we need to learn a lot of things from scratch. While we might have used DispatchQueue.async or other mechanisms to kick off multiple asynchronous tasks in the past, we shouldn't use these older concurrency tools in Swift's new concurrency model. Luckily, Swift Concurrency comes with many features already which means that for a lot of our old uses cases, a new paradigm exists. In this post, you will learn what Swift Concurrency's task groups are, and how you can use them to concurrently perform a lot of...

This post applies to the version of SwiftUI that shipped with iOS 15, also known as Swift 3. To learn how you can present a bottom sheet on iOS 16 and newer, take a look at this post. With iOS 15, Apple introduced the ability to easily implement a bottom sheet with UISheetPresentationController in UIKit. Unfortunately, Apple didn't extend this functionality to SwiftUI just yet (I'm hoping one of the iOS 15 betas adds this...) but luckily we can make use of UIHostingController and UIViewRepresentable to work around this limitation and use a bottom sheet on SwiftUI. In this post,...

We've seen bottom sheets in Apple's apps for a while now, and plenty of apps have followed this pattern. If you're not sure what I mean, it's the kind of sheet that takes up just a part of the screen and can be swiped upwards to take up the whole screen or downwards to be dismissed. Here's an example from Apple's Maps app: To implement a sheet like this, we used to require third party tools, or we needed to get creative and implement this pattern ourselves. With iOS 15, Apple introduced UISheetPresentationController which allows us to implement bottom sheets...