So far in my Combine series I have mostly focussed on showing you how to use Combine using its built-in mechanisms. I've shown you how Combine's publishers and subscribers work, how you can use Combine for networking, to drive UI updates and how you can transform a Combine publisher's output. Knowing how to do all this with Combine is fantastic, but your knowledge is also still somewhat limited. For example, I haven't shown you at all how you can take an asynchronous operation in your existing code, and expose its result using Combine. Luckily, that is exactly what I'm going...

Oftentimes when you're working with Combine, you'll have publishers that produce a certain output. Sometimes this output is exactly what you need, but often the values that are output by a publisher need to be transformed or manipulated somehow before they are useful to their subscribers. The ability to do this is a huge part of what Combine is, what makes it so powerful, and Functional Reactive Programming (FRP) in general. In this week's post, I will show you several common operators that you can use to transform the output from your publishers and make them more useful. If you've...

So far in my series of posts about Combine, we have focussed on processing values and publishing them. In all of these posts, I used the sink method to subscribe to publishers and to handle their results. Today I would like to show you a different kind of built-in subscriber; assign(to:on:). This subscriber is perfect for subscribing to publishers and updating your UI in response to new values. In this post, I will show you how to use this subscriber, and I will show you how to avoid memory issues when using assign(to:on:). Using assign(to:on:) in your code If you've...

In Combine, everything is considered a stream of values that are emitted over time. This means that sometimes a publisher can publish many values, and other times it publishes only a single value. And other times it errors and publishes no values at all. When your UI has to respond to changing data, or if you want to update your UI in response to a user's actions, you might consider the data and user input to both be streams of values. When we looked at networking in my previous post, it was possible to use a built-in publisher that is...

In the past two weeks I have introduced you to Combine and I've shown you in detail how Publishers and Subscribers work in Combine. This week I want to take a more practical route and explore Combine in a real-world setting. A while ago, I published a post that explained how you can architect and build a networking layer in Swift without any third-party dependencies. If you haven't seen that post before, and want to be able to properly follow along with this post, I recommend that you skim over it and examine the end result of that post. This...

In my previous post about Combine, I introduced you to Functional Reactive Programming (FRP) and I've shown you can subscribe to Combine publishers using the sink(receiveCompletion:receiveValue:) method. I also showed you how you can transform the output of publishers using some of its built-in functions like map and collect. This week I want to focus more on how Combine publishers and subscribers work under the hood. By the end of today's post, you should have a clear picture of what Combine's core components are, and how they relate to each other. The topics covered in today's post are the following:...

The Combine framework. Silently introduced, yet hugely important for iOS. It didn't get any attention during the big Keynote at WWDC 2019, but as soon as folks were in the sessions they knew that Combine was going to be huge. It implements a Functional Reactive Programming (FRP) paradigm that's similar to that of Rx which is implemented by RxSwift, except it's made by Apple and has native support on all Apple platforms as long as they are running iOS 13+, iPadOS 13+, macOS 10.15+, watchOS 6+ or tvOS 13+. The fact that Apple created their own FRP framework is a...

Together with iOS 13, Apple announced a new feature called Low Data Mode. This feature allows users to limit the amount of data that’s used by apps on their phone. The low data mode setting is available in the settings app. Whenever a user is on a slow network, a very busy network or on a network that might charge them for every megabyte they download, users might not want to spend their limited data budget on large fancy images or clever prefetching logic. With Low Data Mode, users can now inform your app that they are on such a...